Multiple motor point stimulation increases tetanic knee torque versus conventional single- electrode functional electrical stimulation: implications for functional output and neurorehabilitation

Multiple motor point stimulation increases tetanic knee torque versus conventional single- electrode functional electrical stimulation: implications for functional output and neurorehabilitation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Multiple motor point stimulation increases tetanic knee torque versus conventional single- electrode functional electrical stimulation: implications for functional output and neurorehabilitation Benjamin Kozlowski, Derrick Lim, Meredith Gladish, Arash Arami, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7782510/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract Background Functional electrical stimulation (FES) delivers transcutaneous electrical current to motor nerves to artificially evoke muscle contractions and produce joint torque. In neurorehabilitation, FES is commonly applied via a large surface electrode pair placed over a muscle group – an approach that we here refer to as single-electrode stimulation (SES). However, the torque-generating capacity of SES is limited. Targeting specific regions of high electrical excitability, or motor points, may enhance neuromuscular activation and increase joint torque output. Here we tested whether continuous multiple motor point stimulation (mMPS) increases tetanic knee torque compared with SES in the quadriceps and hamstrings. We also quantified quadriceps recruitment overlap as a secondary aim. We evaluated quadriceps and hamstring responses to mMPS and SES in neurologically intact participants, recording tetanic knee torque and assessing recruitment overlap relative to maximal voluntary contraction (MVC). Results Stimulating all quadriceps motor points produced approximately 51% greater knee extension torque than SES (33.3% MVC vs. 22.1% MVC). In contrast, stimulating all hamstring motor points did not significantly increase knee flexion torque. Within the quadriceps, proximal and intermediate vastus lateralis motor points contributed the most to knee extension torque, whereas the distal motor point had no significant effect. Discrepancies between observed and predicted MPS torques were primarily associated with rectus femoris stimulation, while vastus medialis contributed the least. Conclusions Stimulation of all quadriceps motor points generated 51% greater knee extension torque compared with conventional SES, highlighting the potential of mMPS to improve the effectiveness of FES interventions. Optimization of motor point selection should emphasize proximal and intermediate vastus lateralis sites, while also including vastus medialis. Rectus femoris stimulation should be considered only when channel allocation permits and when the torque benefit outweighs redundancy. In contrast, hamstring stimulation did not yield additional knee flexion torque underscoring muscle-specific limitations. These findings provide practical guidance for electrode placement and channel allocation, suggesting that optimal quadriceps stimulation can be achieved by prioritizing a limited subset of motor points. functional electrical stimulation hamstrings motor point neuromuscular electrical stimulation neurorehabilitation orthotic quadriceps spinal cord injury tetanic torque Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Background Functional electrical stimulation (FES) is a clinically established neurorehabilitation intervention that delivers transcutaneous electrical currents to skeletal muscles, inducing controlled artificial contractions without the need of voluntary command ( 1 , 2 ). FES has been applied to improve local and systemic outputs, including cardiorespiratory fitness ( 3 ), mitigation of muscle degeneration ( 4 , 5 ), and the restoration of functional movements such as walking and standing ( 6 – 8 ). Exercise-based modalities such as FES-rowing and FES-cycling leverage the torque-generating capacity of FES to enable aerobic activity ( 9 , 10 ). The torque produced during FES has been found to be partially influenced by extrinsic parameters governing stimulation delivery, including the spatial configuration and positioning of electrodes, which collectively affect both the quality and quantity of the resulting muscular contractions ( 11 – 15 ). Conventional FES protocols typically adopt a large electrode pair positioned across a muscle compartment in a generalized configuration. In this study, we refer to this method as single-electrode stimulation (SES), which tends to recruit motor units under the electrodes in a nonspecific and spatially fixed manner. As a result, SES typically produces reduced muscle activation compared to activation of the nerve trunk (i.e., peripheral nerve stimulation) suggesting that SES activates only a limited portion of the muscle ( 16 , 17 ). Neurophysiological ( 18 ) and imaging ( 19 , 20 ) studies further confirm that SES activates restricted muscle regions compared to peripheral nerve stimulation or voluntary contractions. Such limitations may impair functional performance and reduce clinical utility, especially at higher stimulation intensities. These constraints highlight the need for more targeted stimulation strategies that can optimize motor unit recruitment across the muscle compartment. Targeting a muscle’s motor point offers a more specific and potentially more effective alternative to SES. Motor point stimulation (MPS) delivers current directly to topographically identified regions of highest electrical excitability of the muscle, engaging neuromuscular pathways more efficiently than SES. Our previous work in the soleus muscle demonstrated that MPS predominantly activates motor nerves and produces activation levels comparable to peripheral nerve stimulation, suggesting more complete recruitment of the muscle ( 21 – 23 ). Beyond the soleus, MPS has been examined in animal preparations ( 24 , 25 ), in able-bodied individuals ( 13 , 26 ), and in neurological populations ( 27 – 29 ), supporting its feasibility across models and clinical contexts. To date, only one study has directly compared MPS with SES. Gobbo et al. ( 30 ) evaluated the tibialis anterior and vastus lateralis and showed that torque evoked by a single MPS site exceeded that of SES. In line with these findings, two review papers have concluded that MPS is advantageous for rehabilitation applications, where greater torque generation and improved performance are critical ( 31 , 32 ). Nevertheless, MPS remains underutilized in clinical practice, in part due to the lack of systematic guidance on which motor points to target within specific muscle groups. This issue is particularly critical in the thigh, a primary site for FES-based exercise therapies ( 9 , 33 – 35 ), where uncertainty over motor point selection limits therapeutic optimization. Topographical mapping studies have identified multiple motor points within the anterior and posterior thigh (~ 7 in the quadriceps; ~4 in the hamstrings) ( 12 , 36 , 37 ), indicating that several distinct sites may serve as targets for evoking torques through MPS at the knee. We previously evaluated this concept at the twitch level by systematically testing all combinations of quadriceps motor points and found that activating all sites produced the greatest twitch torque, with the vastus lateralis contributing disproportionately ( 13 ). These findings highlight the potential of motor point stimulation, but functional FES requires continuous activation to generate fused, tetanic contractions. Thus, it remains unclear whether the advantages observed at the twitch level persist under tetanic multiple motor point stimulation (mMPS), and how interactions among individual motor points influence overall torque output. Addressing this gap is critical for optimizing electrode placement and channel allocation in motor point-based FES protocols. Therefore, the purpose of this study was to systematically evaluate the tetanic torque-generating capacity of continuous mMPS applied to multiple motor points in the quadriceps and hamstrings, and to compare these outputs with SES. A secondary aim was to quantify recruitment overlap under mMPS in the quadriceps femoris muscles by contrasting observed torques with predicted values, in order to distinguish unique from redundant contributions and thereby guide electrode placement. Results Maximal voluntary contraction knee torque There was no difference in MVC post compared to MVC pre following all quadricep (Wilcoxon signed-rank test: mean change = 5.73 ± 17.11; Z = 0.646, p = 0.519, r = 0.186) and hamstring (mean change = -1.21 ± 4.49 ; t( 11 ) = -0.93, p = 0.371, d z = 0.269) FES conditions, suggesting that the stimulation protocols did not induce measurable fatigue and was not needed to be considered for subsequent analysis. Knee torque between motor point and single-electrode stimulation conditions Group data for normalized iMPS, mMPS, and SES quads mean peak knee extension torques are summarized in Fig. 2 A. Comparison between iMPS and mMPS conditions relative to SES quads revealed a significant main effect of stimulation (F(14, 153) = 37.67, p < 0.001, η²ₚ = 0.529). Post hoc pairwise comparisons using Dunnett’s test revealed all iMPS conditions ( VM d , VM p , RF d , RF p , VL d , VL i , VL p ) ( t ( 11 ) = -5.96 to -4.10, all p < 0.001, all d z = -3.66 to -0.27) and one mMPS condition ( VM ) ( t ( 11 ) = -3.95, p = 0.001, d z = -2.20) produced less knee extension torque than SES quads . Knee extension torque produced during single-muscle ( RF , VL ) and paired-muscle ( VM + RF , VM + VL , RF + VL ) stimulation conditions did not differ significantly compared to SES quads (all p > 0.10, d z = -0.074 to 0.595). In contrast, ALL quads produced greater torque than SES quads in 92% (11/12) of participants. Across all participants, ALL quads yielded 50.8% (range: -17.5% to 208.6%) more knee extension torque compared to SES quads (mean: 33.3% MVC vs. 22.1% MVC; t ( 11 ) = 3.68, p = 0.004, d z = 1.06). Group data for normalized iMPS, mMPS, and SES hams mean peak knee flexion torques are summarized in Fig. 2 B. Comparison between iMPS and mMPS conditions relative to SES hams revealed a significant main effect of stimulation (F(6,66) = 7.839, p < 0.001, η²ₚ = 0.416). Post hoc pairwise comparisons using Dunnett’s test revealed all iMPS conditions ( BF lh , BF sh , SM , ST ) (t( 11 ) = -7.80 to -4.94, all p 1.03) and the BF mMPS condition (t( 11 ) = -4.137, p = 0.009, d z = 0.882) produced less knee flexion torque than SES hams . Knee flexion torque produced during all paired-muscle ( BF + SM , BF + ST , SM + ST ) mMPS conditions was not significantly different than SES hams (all p > 0.054, d z >0.502). Across all participants, SES hams produced greater knee flexion torque than ALL hams (mean: 21.0% MVC vs. 18.4% MVC) in 42% (7/12) of participants; however, the group difference was not significant (t( 11 ) = -0.741, p = 0.933, d z = 0.098). Knee torque between multiple motor point stimulation conditions Figure 2 A summarizes the group data on normalized knee extension torques. Repeated measures ANOVA revealed a significant main effect of stimulation across quadricep mMPS conditions (F(6, 66) = 27.247, p < 0.001, η²ₚ = 0.712). Post hoc pairwise comparisons using Bonferroni correction indicated that all single-muscle conditions produced less torque than all paired-muscle and ALL quads conditions (all t( 11 ) < -1.078, all p 0.802). ALL quads produced significantly greater torque than all mMPS conditions (all t ( 11 ) > 4.40, all p 0.67), except for the VM + VL condition, which did not differ significantly ( t ( 11 ) = 3.146, p = 0.195, d z = 0.429). Figure 2 B summarizes the group data on normalized knee flexion torque. Repeated measures ANOVA revealed a significant main effect on stimulation across hamstring mMPS conditions (F(6, 66) = 7.838, p 4.10, both p 1.030). For paired-muscle mMPS conditions, BF + SM and SM + ST produced less torque than ALL hams (both t( 7 ) > 4.33, both p 0.289); however, BF + SM did not produce significantly different knee flexion torque than ALL hams (t( 7 ) = 0.533, p = 1.000, d z = 0.079). Contribution of individual motor points to knee extension torque Summary data of coefficients for each quadriceps motor point are presented in Fig. 3 . The mixed-effects model indicated that all motor points contributed significantly to knee extension torque, except VL d ( p = 0.438). The largest contributions were observed for VL p and VL i , followed by RF d , RF p , and VM p , with VM d showing a smaller but significant effect. Participant-level variability was minimal (variance = 0.003), suggesting consistent torque responses across individuals. These findings highlight the dominant roles of the vastus lateralis and rectus femoris motor points in torque generation. Differences in observed and expected knee extension joint torque Group data comparing τ obs and τ pre for all quadricep MPS combinations are found in Fig. 4 . Paired t tests for single-muscle mMPS condition revealed no significant difference between τ obs and τ pre for VM and RF (all t ( 11 ) 0.059, all d z < -0.609), whereas τ obs was significantly less than τ pre for VL ( t ( 11 ) = -2.300, p = 0.042, d z = -0.664). Repeated measures ANOVA was significant in the main effect on stimulation across τ obs and τ pre for VM + RF (F( 4 , 44 ) = 5,459, p = 0.001, η²ₚ = 0.332), and VM + VL (F( 4 , 44 ) = 4.827, p = 0.003, η²ₚ = 0.305), but no Dunnett post hoc revealed significant between any τ obs and all τ pre (all t ( 11 ) 0.096, all d z < -0.462). For RF + VL , there was a significant effect on stimulation across τ obs and τ pre (F( 4 , 44 ) = 11.746, p < 0.001, η²ₚ = 0.516), with Dunnett post hoc revealing τ obs being significant less than all (4/4) τ pre (all t ( 11 ) < -3.534, all p < 0.009, all d z < -1.020). Further, for ALL quads, there was a significant effect on stimulation across τ obs and τ pre (F(14, 154) = 9.452, p < 0.001, η²ₚ = 0.462), with Dunnett post hoc revealing τ obs being significant less than all (14/14) τ pre (all t ( 11 ) < -2.919, all p < 0.05, all d z < -0.636) Linear regressions comparing τ obs and τ pre across mMPS conditions are shown in Fig. 5 A, with metrics and alignment scores found in Table 1 . One-sample t tests of the regression slopes against unity indicated that slopes were generally less than 1, except for [ VM + RF ] (slope = 0.990, t = -0.828, p = 0.425, R ² = 0.819, RMSE = 0.040, F ₁,ₙ₋₂ = 45.183) and [ VM + VL ] (slope = 1.011, t = 1.120, p = 0.287, R ² = 0.894, RMSE = 0.037, F ₁,ₙ₋₂ = 84.624), indicating that activation of both vastus medialis motor points offsets possible muscle activation overlap stemming from rectus femoris and vastus lateralis MPS. The distribution of slopes was right-skewed, indicating that most mMPS combinations underestimated observed torque relative to theoretical predictions (Fig. 5 B). In contrast, intercepts demonstrated an inverse pattern, with positive offsets becoming more prominent as slopes deviated below unity. This compensation effect was confirmed by a significant negative correlation between slopes and intercepts ( r = -0.906, p < 0.001), suggesting that under-proportional scaling (slope < 1) was systematically offset by upward shifts in the regression line (Fig. 5 B). Calculation of activation scores revealed that τ obs and τ pre comparisons involving VM (i.e., stimulation for both vastus medialis motor points) had the best linear agreement, suggesting minimal intermuscular activation overlap, offsetting torque deviation attributed to vastus lateralis and rectus femoris (Table 1 ). Table 1 Summary of Linear Regression Slopes and Intercepts for Quadriceps mMPS τ obs and τ pre Comparisons Reference Number mMPS Condition τ pre Combination Slope Y-intercept Alignment Score 11 VM + VL VM , VL 1.011 -0.021 0.032 7 VM + RF VM , RF 0.994 -0.026 0.032 27 ALL quads VM , RF + VL 0.966 -0.008 0.042 9 VM + VL VM, VL d , VL i , VL p 0.973 -0.045 0.072 26 ALL quads VM d , VM p , RF + VL VM + VL 0.849 0.018 0.169 3 VL VL 0.810 0.008 0.198 6 VM + RF VM , RF , VL 0.740 0.022 0.262 10 VM + VL VM d , VM p , RF 0.751 0.042 0.291 20 ALL quads VL , VM + RF 0.688 0.031 0.343 21 ALL quads VM , RF , VL d , VL i , VL p 0.646 0.027 0.381 8 VM + VL VM d , VM p , VL d , VL i , VL p 0.654 0.049 0.395 29 ALL quads VL , VM + RF 0.659 0.062 0.403 28 ALL quads RF , VM + VL 0.645 0.062 0.417 22 ALL quads VM d , VM p , RF , VL 0.599 0.059 0.460 15 RF + VL RF , VL 0.589 0.054 0.465 2 RF RF 0.569 0.041 0.472 24 ALL quads VM + RF , VL d , VL i , VL p 0.590 0.069 0.479 5 VM + RF VM , RF d , RF p 0.576 0.055 0.479 18 ALL quads VM d , VM p , RF , VL d , VL i , VL p 0.546 0.064 0.518 17 ALL quads VM , RF d , RF p , VL d , VL i , VL p 0.534 0.061 0.527 23 ALL quads VM , RF d , RF p , VL 0.529 0.082 0.553 25 ALL quads VM + VL , RF d , RF p 0.516 0.098 0.582 4 VM + RF VM d , VM p , RF d , RF p 0.488 0.071 0.583 1 VM VM 0.463 0.046 0.583 13 RF + VL RF , VL d , VL i , VL p 0.464 0.079 0.615 14 RF + VL RF d , RF p , VL 0.459 0.082 0.623 16 ALL quads VM d , VM p , RF d , RF p , VL d , VL i , VL p 0.463 0.089 0.626 19 ALL quads VM d , VM p , RF d , RF p , VL 0.474 0.100 0.629 12 RF + VL RF d , RF p , VL d , VL i , VL p 0.420 0.081 0.661 The random forest regression model (Fig. 6 ) demonstrated strong in-sample performance in predicting the mean quadricep TDI using observed values, achieving an R ² of 0.958 and RMSE of 0.020. However, when evaluated using 5-fold cross-validation, the model showed reduced generalizability, with an average R ² of 0.509 and RMSE of 0.057. Feature importance analysis revealed that rectus femoris MPS conditions ( RF , RF d , RF p ) were the strongest contributors to TDI variance, suggesting a dominant role of rectus femoris stimulation in driving deviations from linear torque summation. In contrast, vastus medialis MPS conditions ( VM d , VM, VM + VL ) contributed the least, indicating a comparatively minor influence on TDI, resulting in better alignment between τ obs and τ pre . Discussion Quadriceps mMPS enhances knee extension torque output beyond SES Stimulation of all quadriceps motor points produced ~ 51% greater knee extension torque compared with conventional SES (33.3% MVC vs. 22.1% MVC) (Fig. 2 A). This finding shows that mMPS engages a broader portion of the quadriceps than SES quads , supporting its potential to improve orthotic performance and exercise-based neurorehabilitation applications. In particular, this enhancement could translate into improved outcomes for FES-cycling and FES-rowing, where torque production from the quadriceps is essential for generating sufficient power and sustaining aerobic workloads ( 9 , 10 , 33 – 35 ). Our results extend prior observations at the twitch level, where activating all quadriceps motor points yielded the largest summed torque, disproportionately driven by vastus lateralis ( 13 ). Importantly, the present study demonstrates that this advantage persists under sustained tetanic stimulation, which more closely approximates the continuous activation required for functional movements. These findings also corroborate Gobbo et al. ( 30 ) who showed that a single motor point in tibialis anterior and vastus lateralis generated greater tetanic torque than SES, thereby reinforcing the generalizable superiority of motor point targeting across muscle groups. From a mechanistic perspective, the greater torque observed with quadriceps mMPS likely reflects a broader and more distributed motor unit recruitment compared with SES quads . Single-electrode stimulation activates fibers predominantly beneath the electrode pair in a spatially fixed manner, whereas MPS exploits anatomically defined loci of excitability, enabling recruitment of motor axons that might otherwise remain inaccessible ( 19 , 20 , 31 , 32 ). This mechanism is supported by neurophysiological evidence that SES stimulates a restricted subset of the muscle compared with voluntary activation or peripheral nerve stimulation ( 16 – 18 ). Thus, mMPS may more closely approximate physiological recruitment patterns and generate stronger contractions. Motor point contributions within the quadriceps The present study identified the proximal and intermediate vastus lateralis motor points ( VL p , VL i ) as the dominant contributors to knee extension torque, consistent with the structural and physiological prominence of the vastus lateralis (Fig. 3 ). Anatomical and imaging studies have shown that the vastus lateralis accounts for the largest proportion of quadriceps strength (~ 40%) compared with the vastus medialis (~ 25%) and rectus femoris–vastus intermedius (~ 35%) ( 44 , 45 ). This regional dominance likely explains the disproportionately high knee extension torque observed when stimulating VL p and VL i . In contrast, the vastus medialis contributed more modest absolute torque (Fig. 3 ), which may reflect its smaller cross-sectional area and more oblique fiber orientation ( 44 , 46 ). Nevertheless, inclusion of vastus medialis motor points consistently enhanced torque generation with minimal redundancy. Its anatomical compartmentalization allows it to activate regions under-recruited by SES quads ( 19 , 20 , 31 , 32 ), complementing the vastus lateralis and improving overall recruitment heterogeneity. This supports the functional importance of VM inclusion despite its smaller individual contribution ( 45 ). Rectus femoris, by comparison, contributed inconsistently to torque output, with variable effects (Figs. 4 , 5 ) Given its biarticular structure and smaller proportional role in knee extension, rectus femoris appears to be a less reliable contributor compared with the vastus lateralis and medialis (Fig. 6 ). Collectively, these findings align with prior reports that MPS achieves more complete muscle activation than SES, which often under-recruits regions such as the vastus medialis and lateralis ( 16 – 18 , 30 ). By optimizing motor point selection, stimulation can engage a broader and more efficient portion of the quadriceps compared with conventional SES, supporting both orthotic performance and potential therapeutic benefits. Recruitment overlap within the quadriceps A secondary aim of this study was to assess recruitment overlap by comparing observed torque with linear predictions from individual motor point contributions. This analysis provides insight into the efficiency of channel allocation – whether additional stimulation sites uniquely increase torque or simply activate fibers already recruited by other sites. The largest discrepancies between observed and predicted torques were observed with rectus femoris stimulation, indicating substantial overlap (Figs. 4 – 6 ). This may stem from current spread into neighboring quadriceps motor point domains or complex intertendinous coupling between quadriceps heads and the quadriceps tendon ( 47 , 48 ), which may contribute to redundant torque output Such overlap reduces the efficiency of stimulation, as additional channels contribute less unique torque relative to their cost in complexity and participant burden. In contrast, vastus medialis stimulation was associated with minimal redundancy, suggesting that it engages a relatively distinct pool of motor units not accessed by vastus lateralis or rectus femoris stimulation. These findings carry practical implications. When optimizing channel allocation for MPS, priority should be given to motor point sites that both contribute significant torque and minimize overlap – namely proximal and intermediate vastus lateralis, together with vastus medialis. Rectus femoris stimulation should be considered only when additional channels are available and when its incremental torque benefits outweigh the cost of redundancy. Such a selective approach aligns with recommendations from prior work emphasizing that maximizing efficiency is as important as maximizing torque when designing mMPS stimulation protocols ( 13 , 30 ). Hamstrings response to mMPS In contrast to the quadriceps, stimulation of all hamstring motor points did not significantly increase knee flexion torque relative to SES (Fig. 2 B). This limited effect likely reflects both physiological and methodological constraints. Motor point mapping has demonstrated that the hamstrings possess fewer and more variably located sites compared to the quadriceps ( 36 ), with deeper locations of the semimembranosus and biceps femoris short head requiring higher stimulation currents for motor point identification in the present study, suggesting less accessible access using transcutaneous stimulation. This may have limited the torque-generating potential of these sites before participant tolerance was reached. Further, in the current study, participants were seated such that the stimulating electrodes were compressed between the seating surface and the skin, which may have altered electrode-tissue contact. Additionally, deformation of the underlying hamstrings could have influenced current distribution, thereby affecting the effective stimulation delivered to the muscle in both MPS and SES hams conditions, limiting knee flexion torque production from both FES methods. Limitations Several limitations should be acknowledged. First, the present study was conducted in neurologically intact participants, and it remains uncertain whether the same torque gains and recruitment patterns would generalize to individuals with neurological impairments, where muscle atrophy, spasticity, and altered excitability may influence outcomes ( 27 – 29 ). Second, we used a finite number of surface electrodes, which constrained the spatial resolution of motor point targeting. Although we attempted to identify and stimulate all accessible motor points, deeper sites or those with high interindividual variability may have been missed ( 36 ). Third, we evaluated tetanic contractions under isometric conditions, which may not fully capture the dynamic demands of functional FES applications such as cycling, walking, or standing. Finally, we normalized torque to maximal voluntary contraction, which provides a useful benchmark in neurologically intact participants but may not directly translate to clinical populations with impaired voluntary control. Conclusions This study demonstrates that stimulation of all quadriceps motor points generated 51% greater torque compared with conventional SES, highlighting the potential of mMPS to improve the effectiveness of FES interventions. Second, the largest torque contributions were derived from proximal and intermediate vastus lateralis sites, together with vastus medialis, indicating that these should be prioritized for optimized motor point selection. Third, rectus femoris stimulation produced torque but also introduced substantial overlap, suggesting it should be considered only when channel allocation permits and when the torque benefit outweighs redundancy. In contrast, stimulation of all hamstring motor points did not yield additional torque, highlighting muscle-specific constraints. These findings provide practical guidance for electrode placement and channel allocation, suggesting that optimal quadriceps stimulation can be achieved by prioritizing a limited subset of motor points. Taken together, they establish a framework for refining FES strategies to maximize torque generation, minimize redundancy, and ultimately improve functional outcomes in neurorehabilitation. Methods Participants Twelve neurologically intact participants (9 males, 3 females; age: 25.5 ± 4.3 yrs, body mass: 72.3 ± 15.3 kg, height: 175.8 ± 6.7 cm) took part in this study. All participants self-reported no peripheral or central neuromuscular, osteological, or cardiovascular conditions. To avoid any confounding effects from fatigue or delayed-onset muscle soreness on artificially- or voluntarily induced muscle contractions, participants were asked to abstain from any intensive exercise of the lower limbs a minimum of 48 hours prior to undergoing experimental procedures. All participants provided written and verbal informed consent prior to participation. The experimental procedures were approved by the Institutional Research Ethics Board. Motor point identification Prior to experimental procedures, motor points for the right anterior and posterior thigh were identified. In total, up to seven and four motor points were expected to be identified for the quadriceps femoris and for the biceps femoris, respectively ( 36 ). To account for interindividual differences in motor point positions ( 13 , 38 , 39 ), locations were initially estimated using bony and soft tissue anatomical landmarks and confirmed by tracking the skin with a cathodic pen electrode (contact surface: 2 mm 2 ) (Chattanooga Physio, DJO Global, Chattanooga, TN, United States) delivering a low-intensity (< 15 mA) pulse at 2 Hz. The corresponding anode (5 cm x 10 cm; Axelgaard Manufacturing Co. Ltd., Fallbrook, CA, United States) was centered about the antagonist group. Motor points were tracked and their locations confirmed through manual palpation of the surrounding musculature and visual inspection of the largest skin deformation from muscle contracture in response to the smallest delivered electrical current ( 31 , 36 , 39 ). All quadriceps motor points were identified on the right thigh with the participant positioned in 80° of hip flexion and 90° of knee flexion (anatomical position = 0°), as measured relative to the anatomical axes of rotation using an analog goniometer. Up to seven motor points were located for the superficial quadriceps femoris muscles: two for the vastus medialis (distal, VM d ; and proximal, VM p ), two for the rectus femoris (distal, RF d ; and proximal, RF p ), and three for the vastus lateralis (distal, VL d ; intermediate, VL i ; and proximal, VL p ) ( 36 ). For hamstring motor point identification, participants were positioned prone with the knee flexed to 70° relative to full extension (0°). Up to four motor points were located: two for the biceps femoris (long head, BF lh ; and short head, BF sh ), one for the semimembranosus ( SM ), and one for the semitendinosus ( ST ) ( 36 ). All motor points were marked on the skin using indelible ink. Motor point locations for all quadriceps (seven total) and hamstrings (four total) muscles were identified for 12/12 participants. Stimulating electrode placements: quadriceps configuration Prior to surface electrode fixation, the skin was cleaned using alcohol swabs (70% v/v), being carful not to remove the motor point markings. For the MPS conditions, individual self-adhesive cathode-anode electrode pairs (two 5 x 5 cm) were adopted for each motor point (Fig. 1 A). The cathode was centered over the motor point, while the anode was positioned, in parallel, either slightly proximal or distal to the cathode over the respective muscle. An edge-to-edge interelectrode distance of approximately 2 cm was aimed for; however, this spacing was not always feasible due to limited surface area on the thigh, particularly without encroaching on the adductor or hamstring muscle groups. In total, seven cathode-anode pairs were adopted (14 total electrodes). For the quadricep SES ( SES quads ) condition across the anterior thigh, a large self-adhesive electrode pair (7.5 cm × 10 cm) was placed in a proximal-distal configuration (Fig. 1 B). The proximal cathode was oriented transversely, with its superior margin positioned approximately 10 cm distal to the inguinal groove and slightly lateral, positioned over the proximal bodies of the vastus lateralis and rectus femoris muscles, while avoiding the femoral triangle. The distal anode was also oriented transversely, with the inferior margin positioned approximately 5 cm proximal to the base of the patella ( 17 ). To minimize potential bias in experimenter placement of SES quads electrodes relative to participants’ motor points, markings indicating motor point locations were erased using rubbing alcohol until no visible pigment remained. These motor point locations were not referenced during SES quads electrode placement. Stimulating electrode placements: hamstrings configuration For the MPS condition, individual cathode-anode electrode pairs (5 × 5 cm each) were assigned to each motor point (Fig. 1 A). As the hamstring muscles are biarticular that feature a pelvic origin, changes in hip angle can lengthen their muscle fibers ( 40 ), which may inadvertently migrate the motor point relative to the joint angle they were initially searched for ( 26 , 41 ). To account for potential superior motor point migration due to differences in hip angle between motor point screening (anatomically neutral) and experimental evaluation (80° flexion) in the present study, the cathode was centered approximately 1 cm superior to the identified motor point and aligned to follow the respective muscle fiber orientation as closely as possible. The anode was positioned either proximally or distally along the same muscle, based on available space. In total, four cathode-anode pairs were adopted (eight total electrodes). For the hamstring SES ( SES hams ) condition across the posterior thigh, a large (7.5 cm × 10 cm) cathode-anode pair was positioned proximally and distally (Fig. 1 B). The proximal cathode was oriented transversely, immediately distal to the inferior gluteal fold along the midline of the thigh. The distal anode was also oriented transversely, with its inferior margin positioned approximately 3 cm superior to the center of popliteal fossa, superimposing the surface impressions of the distal hamstring tendons. Markings denoting motor point locations were erased and not considered when positioning the SES hams electrodes. Pre-experimental interventions In order to evaluate artificially induced knee extension and knee flexion isometric tetanic torques induced from FES (MPS and SES) of the thigh, participants were comfortably seated with their right knee joint aligned with the center of rotation of a joint dynamometer (Biodex System 3, Biodex Medical Inc., Shirly, NY, United States). For quadricep FES conditions, the hip was flexed at 80° and knee flexed at 90° (anatomical position = 0° reference) in order to position the quadriceps in an advantageous muscle length to evoke larger torques ( 42 ). For hamstring FES conditions, the hip was flexed at 80° and knee flexed 70°. Inelastic cushioned restraints were applied across the torso and thigh to stabilize the body and mitigate any extraneous joint motion that might confound the assessment of knee torque output during experimental procedures. The leg was secured to the dynamometer attachment arm with a cushioned restraint positioned above the ankle joint, with the foot allowed to hang freely. To enable interindividual comparisons of FES-induced knee torque, participants performed two maximal voluntary contractions (MVCs) of knee extension and flexion for 5 seconds, with strong verbal encouragement, each separated by a 1-minute rest. Participants were instructed to ‘contract as strong and as fast as possible’ while minimizing hip involvement, ensuring that the movement was isolated to knee extension and flexion. Real-time torque traces were displayed on a computer monitor to participants to facilitate maximal effort during contractions. The average maximal knee torque from the steady-state torque profile across both MVC trials was used to normalize all FES-induced torque values. To establish the current amplitude for FES conditions, the maximal tolerable stimulation intensity (MTSI) was individually determined for each individual motor point and SES electrode configurations and subsequently used for experimental evaluations. A designated neuromuscular electrical stimulation device (Chattanooga Continuum, Wilmington, DE, United States) delivered an asymmetric, charge-balanced cathodic waveform (50 Hz frequency, 400 µs pulse width) for all FES sites. Stimulation was manually triggered and carefully controlled by the experimenter using an external push button. The MTSI for each FES site was determined by gradually increasing stimulation from 5 mA in 5 mA steps, applied for 3 s at each increment, until the participant’s tolerance threshold was reached. The intensity was then adjusted in ± 1 mA increments to precisely establish the MTSI. The experimenter continually assessed the participant's ability and willingness to tolerate higher currents before increasing the stimulation intensity. To limit transient fatigue and discomfort from influencing stimulation tolerance, FES conditions were conducted in a pseudorandom order, ensuring that motor points from the same muscle were not evaluated in immediate succession. Participants were instructed to consider the determination of the MTSI at each FES site independently, without using the sensations from other sites to influence their judgment for another. For the successful application of the final MTSI in experimental testing, the following criteria had to be met: ( 1 ) the MTSI induced a fused, nonfasciculated muscle state (visually confirmed), in which a steady-state torque profile was registered; ( 2 ) no exogenous joint movement, either voluntary or FES-induced, was observed, as confirmed through visual inspection and manual palpation of adjacent or antagonistic muscles (e.g., flexion/extension of the torso, hamstring contraction during quadriceps stimulation, quadriceps contraction during hamstring stimulation); and ( 3 ) the stimulation amplitude was tolerated by the participant. If exogenous joint movement was visually observed (e.g., hip extension/flexion), the stimulation intensity was finely adjusted about the MTSI until only extension (quadricep FES) or flexion (hamstring FES) of the knee was produced, with minimal adjacent joint movement. If all criteria were satisfied, the designated current was recorded for each FES site and were adopted for all experimental conditions thereafter. In the current study, two participants reached the maximal stimulator output (100 mA) for several motor points, which was then adopted for testing. Consequently, it remains uncertain whether the final 100 mA represented their true tolerations for those sites. Experimental procedures To evaluate the potential of FES-induced tetanic torque production at the motor points of the thigh, ‘individual MPS’ (i.e., direct stimulation of each motor point separately, iMPS), and inter- and intramuscular ‘multiple MPS’ (i.e., direct stimulation of more than one motor point, mMPS) conditions were assessed. The theoretical number of motor point combinations for the quadriceps and hamstrings are 127 (2⁷ – 1) and 15 (2⁴ – 1), respectively. However, practical limitations – including testing duration, FES-induced muscle fatigue, and participant burden –made it infeasible to evaluate all possible tetanic stimulation combinations within a single session, particularly given day-to-day variations in tolerance and performance across sex and session number ( 43 ). Therefore, to evaluate the tetanic torque-generating potential of mMPS, we restricted our analysis to muscle-specific motor point configurations. This included stimulation of individual motor points, all motor points within a single muscle, paired muscles, and compartmental activation. This framework enabled investigation of torque recruitment dynamics in response to mMPS. For the quadriceps, 13 total MPS conditions were evaluated, comprising both iMPS and mMPS protocols. The iMPS conditions involved the independent stimulation of the seven motor points ( VM d , VM p , RF d , RF p , VL d , VL i , VL p ). The mMPS conditions included: ( 1 ) single-muscle MPS, defined as the simultaneous stimulation of all motor points within a single muscle (e.g., VM d and VM p for vastus medialis), for a total of three conditions ( VM , RF , VL ); ( 2 ) paired-muscle MPS, defined as the simultaneous stimulation of all motor points from two muscles (e.g., VM d , VM p , RF d , and RF p for vastus medialis and rectus femoris), for a total of three conditions ( VM + RF , VM + VL , RF + VL ); and ( 3 ) ALL quads MPS, involving the simultaneous stimulation of all seven quadriceps motor points, comprising one condition. For the hamstrings, nine total MPS conditions were evaluated, consisting of both iMPS and mMPS protocols. The iMPS conditions involved the independent stimulation of four single motor points ( BF lh , BF sh SM , ST ). The mMPS conditions included: ( 1 ) single-muscle MPS, for a total of three conditions; here, only the biceps femoris contained more than one motor point, yielding one condition. Because semimembranosus and semitendinosus each have only one motor point ( 36 ), their evaluations were categorized under single-muscle MPS rather than iMPS; ( 2 ) paired-muscle MPS, for a total of three conditions ( BF + SM , BF + ST , SM + ST ); and ( 3 ) ALL hams MPS, comprising one condition. The iMPS conditions were administered in a block-randomized order, with the constraint that no two motor points from the same muscle were tested consecutively. For the mMPS conditions, stimulation began with single-muscle MPS, followed by paired-muscle MPS (randomized within their respective block), and concluded with stimulating all motor points. To minimize fatigue-related bias, single-muscle MPS was tested before paired-muscle MPS. This sequence was chosen to reduce the risk of underestimating knee torque due to potential fatigue carry-over from conditions involving a greater number of stimulated motor points. The overall sequence – iMPS followed by mMPS – was kept consistent across all participants to ensure standardization. Each FES condition consisted of two continuous stimulation trials, delivered using a 1:2:1 stimulation duty cycle: 6 seconds of stimulation, followed by 12 seconds of rest (no voluntary or FES-induced contractions), and then another 6 seconds of stimulation (total condition duration = 24 seconds), resulting in two submaximal steady-state torque outputs (Fig. 1 C). This stimulation protocol was standardized across all quadriceps and hamstring locations for iMPS, mMPS, and SES conditions. A 2-minute rest period was provided between each FES condition. After completing all MPS conditions, the same stimulation sequence was applied using the respective SES configuration. All quadriceps FES trials were completed first, followed by all hamstring trials, with a minimum 5-minute rest period separating the two muscle groups. Following all respective quadriceps MPS and hamstring MPS conditions, one final MVC ( MVC post ) was performed for knee extension and knee flexion and compared to MVC pre to assess whether fatiguing effects took place over the course of the experimental session. Data collection and analysis All participant knee torque data were collected using LabChart software (LabChart Pro Modules 2018, version 8). Knee torque signals (N·m) were recorded and sampled at 2000 Hz using a 12-bit analog-to-digital data acquisition system (PowerLab System 16/30, ADInstruments, Bella Vista, Australia). Evoked knee torque was evaluated by identifying the peak torque within a 3- to 4-second window of steady-state output, and then geometrically averaging these values from both 6-second contractions for each FES condition. All mean knee torque values were normalized to each participant’s mean preintervention MVC ( MVC pre ) and expressed as a percentage (% MVC) to be used for group comparisons. To estimate the contribution of individual quadriceps motor points to knee extension torque, we fitted a linear mixed-effects model with normalized knee extension torque (% MVC) as the dependent variable. The seven quadricep motor points ( VM d , VM p , RF d , RF p , VL d , VL i , VL p ) were entered as binary fixed effects (1 = activated, 0 = not), and participant was included as a random intercept to account for repeated measures. Model coefficients were interpreted as average motor point contributions conditional on the others, with 95% confidence intervals reported. For presentation, coefficients were expressed as percentage contributions by dividing each motor point coefficient by the sum of all motor point coefficients plus the intercept and multiplying by 100. Previous studies have reported discrepancies between observed torque (τ obs ) from artificially-induced contractions and the theoretically predicted torque (τ pre ) when multiple quadricep motor points were simultaneously activated ( 13 , 25 ). In the current study, under the assumption that FES selectively and independently recruits nonoverlapping muscle subdomains during continuous delivery, knee extension torque output from iMPS and mMPS quadricep conditions was compared against τ pre defined as the linear sum of τ obs from any combination of conditions activating the same set of motor points as the target mMPS condition. Each stimulation condition – whether targeting an individual motor point, single-muscle, paired-muscle, or all motor points – was encoded in a binary activation matrix A ∈ {0,1} m x n , where m is the total number of stimulation conditions (including both iMPS and mMPS) and n is the number of topographically distinct quadricep motor points (7 total). Each row of A corresponds to a stimulation condition, and each column indicates whether a specific motor point was activated ( 1 ) or not (0). For a given composite stimulation condition i , all possible subsets C i ⊆ {1,…, m } of stimulation conditions were generated such that their combined motor point activations exactly matched those of condition i , without double-counting any motor point. This constraint can be expressed as: $$\:\left(1\right)\:\:\sum\:_{j=1}^{n}{A}_{ij}=\:\sum\:_{k\in\:{C}_{i}}\sum\:_{j=1}^{n}{A}_{kj}\:\left(2\right)\:\:\sum\:_{k\in\:{C}_{i}}{A}_{kj\:}\le\:1\:\:\forall\:j=1,\:\dots\:,\:n$$ Here, Eq. (1) ensures that the combined stimulation conditions activate exactly the same number of motor points as the composite condition i . Eq. (2) prevents any motor point from being counted more than once when summing MPS conditions, thereby avoiding double-counting motor points. The τ pre for condition i was then calculated as the sum of τ obs , such that: $$\:{\tau\:}_{\text{pre}}^{\left(i\right)}={\sum\:}_{k\in\:{C}_{i}}{\tau\:}_{\text{obs}}^{\left(k\right)}$$ As an example, consider the mMPS condition VM + RF , which simultaneously activates four distinct motor points: VM d , VM p , RF d , and RF p . The τ pre for this condition, \(\:{\tau\:}_{\text{pre}}^{\left(\text{VM}\text{+}\text{RF}\right)}\) , was estimated by summing τ obs from all valid subsets of conditions whose combined motor point activations were topographically equivalent with respect to VM + RF . Specifically, four distinct combinations are possible from the combination of individual, single-muscle, and paired-muscle MPS conditions evaluated in the current study: all relevant iMPS conditions: $$\:{\tau\:}_{\text{pre}}^{\left(\text{VM}\text{+}\text{RF}\right)}={\tau\:}_{\text{obs}}^{\left({\text{VM}}_{\text{p}}\right)}+{\tau\:}_{\text{obs}}^{\left({\text{VM}}_{\text{d}}\right)}+{\tau\:}_{\text{obs}}^{\left({\text{RF}}_{\text{p}}\right)}+{\tau\:}_{\text{obs}}^{\left({\text{RF}}_{\text{d}}\right)}$$ single-muscle VM mMPS and rectus femoris iMPSs: $$\:{\tau\:}_{\text{pre}}^{\left(\text{VM}\text{+}\text{RF}\right)}={\tau\:}_{\text{obs}}^{\left(\text{VM}\right)}+{\tau\:}_{\text{obs}}^{\left({\text{RF}}_{\text{p}}\right)}+{\tau\:}_{\text{obs}}^{\left({\text{RF}}_{\text{d}}\right)}$$ single-muscle RF mMPS and vastus medialis iMPSs: $$\:{\tau\:}_{\text{pre}}^{\left(\text{VM}\text{+}\text{RF}\right)}={\tau\:}_{\text{obs}}^{\left(\text{RF}\right)}+{\tau\:}_{\text{obs}}^{\left({\text{VM}}_{\text{p}}\right)}+{\tau\:}_{\text{obs}}^{\left({\text{VM}}_{\text{d}}\right)}$$ single-muscle VM and RF mMPSs: $$\:{\tau\:}_{\text{pre}}^{\left(\text{VM}\text{+}\text{RF}\right)}={\tau\:}_{\text{obs}}^{\left(\text{VM}\right)}+{\tau\:}_{\text{obs}}^{\left(\text{RF}\right)}$$ Each combination satisfies the constraint that all motor points activated during the VM + RF stimulation are represented exactly once, with no redundancy across constituent subsets. This procedure was applied across all mMPS conditions to generate corresponding τ pre estimates for comparison against the respective experimentally measured τ obs values. In total, 29 τ pre combinations were evaluated for the quadriceps, comprising: 3 for single-muscle MPS (3 condition x 1 τ pre , each); 12 for paired-muscle MPS (3 conditions x 4 τ pre, each), and; 14 for ‘all motor point’ stimulation (1 condition x 14 τ pre ) Next, to quantify the deviation between τ obs and τ pre , a torque discrepancy index (TDI) was calculated for each pair of τ obs and τ pre , such that \(\:TDI\:=\:1-\frac{{\tau\:}_{\text{pre}}^{\left(i\right)}}{{\tau\:}_{\text{obs}}^{\left(i\right)}}\) , where values closer to zero indicate stronger agreement between τ obs and predicted linear sums (τ pre ). The TDI was used as a proxy to quantify discrepancies between τ obs and τ pre , attributed to potential activation overlap from FES and/or mechanical interactions arising from unique muscle geometries and properties. To explore the discrepancy between τ obs and τ pre , a machine learning approach was used to assess the relative contribution of each stimulation condition (including iMPS and mMPS conditions) for the quadriceps. Torque discrepancy index values were used to train a random forest regression model (100 estimators, random state = 42) based on one-hot encoded representations of each stimulation condition. Each MPS combination was decomposed into its constituent MPS condition, forming a binary feature matrix, and the model was trained to predict the mean normalized TDI associated with each combination. To ensure generalizability, 5-fold cross-validation was performed. Feature importance scores were extracted from the trained model to identify the MPS conditions most strongly driving TDI, thereby providing insight into the contributions underlying deviations from linear torque summation. Additionally, to evaluate the agreement between τ pre and τ obs torque responses, linear regression models were fitted for each quadricep mMPS combination. From each regression, the slope and y-intercept were extracted and compared against the ideal case of slope = 1 (perfect proportionality) and intercept = 0 (no systematic offset). To provide a single quantitative measure of agreement, we calculated an alignment score, defined as the Euclidean distance from the optimal point (slope = 1, intercept = 0): $$\:\text{A}\text{l}\text{i}\text{g}\text{n}\text{m}\text{e}\text{n}\text{t}\:\text{S}\text{c}\text{o}\text{r}\text{e}\:=\:\sqrt{{\left(slope\:-\:1\right)}^{2}+\:{\left(Y-intercept\right)}^{2}}$$ This metric integrates both proportional accuracy (slope) and systematic bias (intercept), with lower values reflecting closer alignment between τ pre and τ obs . In this framework, mMPS combinations with the smallest alignment scores were interpreted as providing better linear alignment between τ pre and τ obs . We estimated additive motor point contributions with a linear mixed-effects model. Linear agreement between τ pre and τ obs was assessed via simple regression (slope, intercept, alignment score), and factors associated with TDI were examined using a random forest regressor with 5-fold cross-validation. Statistical analysis Prior to statistical analysis, neuromechanical data were assessed for normality using the Shapiro–Wilk test, with appropriate parametric or nonparametric tests subsequently applied. To evaluate whether participant fatigue occurred as a result of the experimental interventions, a paired-samples t test was used to compare pre- and postexperimental MVC values ( MVC ₚ r ₑ vs. MVC ₚₒₛₜ). These normalized torques were analyzed separately for knee extension and knee flexion. Prior to all repeated-measures analyses of variance (ANOVA), the assumption of sphericity was assessed using Mauchly’s test. When sphericity was violated, Greenhouse-Geisser corrections were applied to adjust the degrees of freedom accordingly. To compare torque outputs between mMPS and conventional SES, separate repeated-measures ANOVAs with Dunnett-adjusted post hoc comparisons were conducted for the quadriceps and hamstrings. These analyses evaluated differences in normalized peak knee torque across 13 quadriceps MPS conditions (seven iMPS and six mMPS) and eight hamstring MPS conditions (four iMPS and four mMPS), with each condition compared to its respective SES control. To further assess differences among the mMPS conditions, additional repeated-measures ANOVAs with Bonferroni-adjusted pairwise comparisons were performed separately for each muscle group. This two-tiered analytic approach was implemented to preserve statistical power while appropriately controlling for multiple comparisons. Conducting a single omnibus ANOVA with all possible pairwise comparisons (105 for quadriceps, 45 for hamstrings) would have substantially inflated the risk of Type I error and reduced the sensitivity to detect meaningful effects. Observed and predicted torques were compared to assess the degree of nonlinearity in torque summation and the relative contribution of mMPS conditions to gauge activation overlaps. For single-muscle mMPS conditions, which each comprised only one τₚ r ₑ condition, paired t tests were performed comparing their respective τ obs and τₚ r ₑ. For paired-muscle and ALL quads mMPS conditions, repeated-measures ANOVA was conducted to assess whether τₚ r ₑ combinations significantly differed from the corresponding τ obs , with Dunnett post hoc tests used to compare each τₚ r ₑ combination directly against its respective τ obs . Linear regression models were fitted for each τₚ r ₑ against τ obs using a leave-one-out approach, where each data point was sequentially omitted and the slope recalculated. Slope coefficients were tested against 1 to evaluate proportional agreement, and y-intercepts were examined for systematic offsets. Model performance was further quantified using R 2 , indicating the proportion of variance in τ obs explained by the τₚ r ₑ, and the root mean square error ( RMSE ), reflecting the average prediction error. Statistical significance was defined as α = 0.05 (two-tailed). Descriptive data in text and table are reported as geometric mean ± standard deviation. Effect sizes were reported as partial eta squared (η²ₚ) for repeated-measures ANOVA, Cohen’s d z for paired-samples and pairwise comparisons, and r for Wilcoxon signed-rank test. All t tests, repeated-measures ANOVA, Bonferroni post hoc tests, effect size calculations, linear mixed-modeling, and Random Forest analyses were conducted using custom Python scripts (version 3.11.4), while Dunnett post hoc tests were performed in R (version 4.4.3). Abbreviations ALL hams , all hamstring motor points ALL quads , all quadricep motor points ANOVA, analysis of variance BF, biceps femoris BF lh , biceps femoris – long head BF sh , biceps femoris – short head FES, functional electrical stimulation iMPS, individual motor point stimulation MPS, motor point stimulation mMPS, multiple motor point stimulation MTSI, maximal tolerable stimulation intensity MVC, maximal voluntary contraction R 2 , coefficient of determination RF, rectus femoris RF d , rectus femoris – distal RF p , rectus femoris – proximal RMSE, root mean squared error SES, single-electrode stimulation SES hams , single-electrode stimulation – hamstrings SES quads , single-electrode stimulation – quadriceps SM, semimembranosus ST, semitendinosus TDI, torque deviation index VL, vastus lateralis VL d , vastus lateralis – distal VL i , vastus lateralis – intermediate VL p , vastus lateralis – proximal VM, vastus medialis VM d , vastus medialis – distal VM p , vastus medialis – proximal η²ₚ, partial eta squared τ obs , observed torque τ pre , predicted torque Declarations Ethics approval and consent to participate The studies involving human participants were reviewed and approved by University Health Network (21-5946) Research Ethics Boards. The participants provided their written informed consent to participate in accordance with the Declaration of Helsinki. Consent for publication All authors read and approved the final manuscript for submission for publication. Funding This study was supported by the New Frontiers in Research Fund (grant no. NFRFE-2022-00620). Benjamin Kozlowski was supported by the Canadian Graduate Scholarship – Masters from the Natural Sciences and Engineering Research Council of Canada. Author Contribution B.K., D.L., and K.M. conceptualized and designed the study. B.K. and M.G. collected the data and performed analyses. B.K., D.L., and K.M. curated, analyzed, and interpreted the data. B.K. and prepared the figures and table. B.K. and K.M. drafted the manuscript. K.M. and A.A. provided funding support and supervision. All authors reviewed and approved the final manuscript. Acknowledgement The authors would like to thank all those who participated in the study. 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Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 20 Nov, 2025 Reviews received at journal 18 Nov, 2025 Reviews received at journal 04 Nov, 2025 Reviews received at journal 29 Oct, 2025 Reviewers agreed at journal 15 Oct, 2025 Reviewers agreed at journal 15 Oct, 2025 Reviewers agreed at journal 14 Oct, 2025 Reviewers agreed at journal 14 Oct, 2025 Reviewers invited by journal 14 Oct, 2025 Editor assigned by journal 09 Oct, 2025 Submission checks completed at journal 08 Oct, 2025 First submitted to journal 04 Oct, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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All quadriceps and hamstring motor points were identified and marked for each participant, with a separate cathode-anode pair assigned to each motor point.\u003c/strong\u003e Single-electrode stimulation sites across the anterior and posterior thighs were positioned based on surface anatomical landmarks. Designated neuromuscular stimulators were used to evoke artificially induced joint torques. Identical stimulation parameters were applied across all FES conditions. Parts of this figure were created with BioRender.com.\u003c/p\u003e","description":"","filename":"fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-7782510/v1/59da7fe0b48ab23de37b40de.png"},{"id":94672601,"identity":"60e7d9ac-9034-4e66-b443-d85f45d86883","added_by":"auto","created_at":"2025-10-29 13:40:45","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":37152625,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eKnee extension (A) and flexion (B) torques produced under iMPS and mMPS conditions, compared to the SES condition. \u003c/strong\u003eIndividual MPS (white) and mMPS conditions – single-muscle (grey), paired-muscle (blue), and all motor-point (dark green) – were compared to the SES condition (orange). Multiple MPS conditions for the quadriceps and hamstrings were analyzed separately. Anatomical schematics of the anterior and posterior thigh illustrate the relative locations of motor points for iMPS conditions (grey scale), and muscles activated during single- and paired-muscle mMPS conditions (bright green). Individual data points are shown as white circles, and geometric means as red circles. Lines connect matched participants across all-MPS and SES conditions for both quadriceps and hamstrings. *, Dunnett post hoc (\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05); horizontal lines, Bonferroni post hoc (\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05).\u003c/p\u003e","description":"","filename":"fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-7782510/v1/ecb1d9a16d286fffed348d46.png"},{"id":94663361,"identity":"4901ce71-2d9a-4252-8879-e612dd3d9b8e","added_by":"auto","created_at":"2025-10-29 12:09:15","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":372464,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePercentage contribution of each quadriceps motor point to knee extension torque, calculated using linear mixed-effects regression. \u003c/strong\u003eBar plots display regression coefficients ± 95% confidence intervals.\u003c/p\u003e","description":"","filename":"fig3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7782510/v1/6811775491f1033e0cc85d20.jpeg"},{"id":94663403,"identity":"78cdc497-d5ae-4d05-a549-0266b9165ad0","added_by":"auto","created_at":"2025-10-29 12:09:16","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":38884248,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eBoxplots of observed and predicted torque combinations across all quadriceps mMPS conditions. \u003c/strong\u003eReference numbers (right index) correspond to the number-matched τ\u003csub\u003epre\u003c/sub\u003e values (shown beneath each predicted torque boxplot), representing the summed τ\u003csub\u003eobs\u003c/sub\u003e combinations for each mMPS condition. #, paired \u003cem\u003et\u003c/em\u003e test; *, Dunnett post hoc (\u003cem\u003ep \u0026lt; \u003c/em\u003e0.05).\u003c/p\u003e","description":"","filename":"fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-7782510/v1/11ac9b78c095322d96994565.png"},{"id":94672270,"identity":"811e6ee2-36ac-40bc-bd2f-0af95abd30d5","added_by":"auto","created_at":"2025-10-29 13:40:06","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":24371873,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLinear regression between predicted and observed torques for all τ\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003epre\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e combinations (A) and corresponding slope and y-intercept metrics (B).\u003c/strong\u003e Panel A shows simple linear regression fits of τ\u003csub\u003eobs\u003c/sub\u003e torque (y-axis) against τ\u003csub\u003epre\u003c/sub\u003e combinations (x-axis) across quadriceps mMPS conditions. Panel B presents the distributions of slope (left) and y-intercept (middle) values (kernel density estimates), and the correlation between slope and y-intercept (right; black line = fit, shaded area = 95% confidence interval), for quadricep mMPS conditions.\u003c/p\u003e","description":"","filename":"fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-7782510/v1/ef8cd6f0344f9d0b71dfc499.png"},{"id":94663366,"identity":"3c9ca736-2c1a-4b5e-a9db-1ffa25dc8f39","added_by":"auto","created_at":"2025-10-29 12:09:15","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":366932,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRandom forest regression feature importance and model performance for predicting the TDI. \u003c/strong\u003eFeature importance (blue bars) indicates the relative contribution of each mMPS condition to the model’s predictions for each TDI combination. The nested regression plot illustrates model performance by comparing actual and predicted TDI values across τ\u003csub\u003epre\u003c/sub\u003e comparisons.\u003c/p\u003e","description":"","filename":"fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-7782510/v1/c9cd089ad64164169a132941.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"Multiple motor point stimulation increases tetanic knee torque versus conventional single- electrode functional electrical stimulation: implications for functional output and neurorehabilitation","fulltext":[{"header":"Background","content":"\u003cp\u003eFunctional electrical stimulation (FES) is a clinically established neurorehabilitation intervention that delivers transcutaneous electrical currents to skeletal muscles, inducing controlled artificial contractions without the need of voluntary command (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). FES has been applied to improve local and systemic outputs, including cardiorespiratory fitness (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e), mitigation of muscle degeneration (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e), and the restoration of functional movements such as walking and standing (\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e). Exercise-based modalities such as FES-rowing and FES-cycling leverage the torque-generating capacity of FES to enable aerobic activity (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). The torque produced during FES has been found to be partially influenced by extrinsic parameters governing stimulation delivery, including the spatial configuration and positioning of electrodes, which collectively affect both the quality and quantity of the resulting muscular contractions (\u003cspan additionalcitationids=\"CR12 CR13 CR14\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eConventional FES protocols typically adopt a large electrode pair positioned across a muscle compartment in a generalized configuration. In this study, we refer to this method as single-electrode stimulation (SES), which tends to recruit motor units under the electrodes in a nonspecific and spatially fixed manner. As a result, SES typically produces reduced muscle activation compared to activation of the nerve trunk (i.e., peripheral nerve stimulation) suggesting that SES activates only a limited portion of the muscle (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). Neurophysiological (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e) and imaging (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e) studies further confirm that SES activates restricted muscle regions compared to peripheral nerve stimulation or voluntary contractions. Such limitations may impair functional performance and reduce clinical utility, especially at higher stimulation intensities. These constraints highlight the need for more targeted stimulation strategies that can optimize motor unit recruitment across the muscle compartment.\u003c/p\u003e\u003cp\u003eTargeting a muscle\u0026rsquo;s motor point offers a more specific and potentially more effective alternative to SES. Motor point stimulation (MPS) delivers current directly to topographically identified regions of highest electrical excitability of the muscle, engaging neuromuscular pathways more efficiently than SES. Our previous work in the soleus muscle demonstrated that MPS predominantly activates motor nerves and produces activation levels comparable to peripheral nerve stimulation, suggesting more complete recruitment of the muscle (\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e). Beyond the soleus, MPS has been examined in animal preparations (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e), in able-bodied individuals (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e), and in neurological populations (\u003cspan additionalcitationids=\"CR28\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e), supporting its feasibility across models and clinical contexts. To date, only one study has directly compared MPS with SES. Gobbo et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e) evaluated the tibialis anterior and vastus lateralis and showed that torque evoked by a single MPS site exceeded that of SES. In line with these findings, two review papers have concluded that MPS is advantageous for rehabilitation applications, where greater torque generation and improved performance are critical (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e). Nevertheless, MPS remains underutilized in clinical practice, in part due to the lack of systematic guidance on which motor points to target within specific muscle groups. This issue is particularly critical in the thigh, a primary site for FES-based exercise therapies (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e), where uncertainty over motor point selection limits therapeutic optimization.\u003c/p\u003e\u003cp\u003eTopographical mapping studies have identified multiple motor points within the anterior and posterior thigh (~\u0026thinsp;7 in the quadriceps; ~4 in the hamstrings) (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e), indicating that several distinct sites may serve as targets for evoking torques through MPS at the knee. We previously evaluated this concept at the twitch level by systematically testing all combinations of quadriceps motor points and found that activating all sites produced the greatest twitch torque, with the vastus lateralis contributing disproportionately (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e). These findings highlight the potential of motor point stimulation, but functional FES requires continuous activation to generate fused, tetanic contractions. Thus, it remains unclear whether the advantages observed at the twitch level persist under tetanic multiple motor point stimulation (mMPS), and how interactions among individual motor points influence overall torque output. Addressing this gap is critical for optimizing electrode placement and channel allocation in motor point-based FES protocols.\u003c/p\u003e\u003cp\u003eTherefore, the purpose of this study was to systematically evaluate the tetanic torque-generating capacity of continuous mMPS applied to multiple motor points in the quadriceps and hamstrings, and to compare these outputs with SES. A secondary aim was to quantify recruitment overlap under mMPS in the quadriceps femoris muscles by contrasting observed torques with predicted values, in order to distinguish unique from redundant contributions and thereby guide electrode placement.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eMaximal voluntary contraction knee torque\u003c/h2\u003e\u003cp\u003eThere was no difference in \u003cem\u003eMVC\u003c/em\u003e\u003csub\u003epost\u003c/sub\u003e compared to \u003cem\u003eMVC\u003c/em\u003e\u003csub\u003epre\u003c/sub\u003e following all quadricep (Wilcoxon signed-rank test: mean change\u0026thinsp;=\u0026thinsp;5.73\u0026thinsp;\u0026plusmn;\u0026thinsp;17.11; \u003cem\u003eZ\u0026thinsp;=\u003c/em\u003e\u0026thinsp;0.646, \u003cem\u003ep\u0026thinsp;=\u003c/em\u003e\u0026thinsp;0.519, \u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.186) and hamstring (mean change = -1.21\u0026thinsp;\u0026plusmn;\u0026thinsp;4.49 ; t(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) = -0.93, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.371, \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e = 0.269) FES conditions, suggesting that the stimulation protocols did not induce measurable fatigue and was not needed to be considered for subsequent analysis.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eKnee torque between motor point and single-electrode stimulation conditions\u003c/h3\u003e\n\u003cp\u003eGroup data for normalized iMPS, mMPS, and \u003cem\u003eSES\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e mean peak knee extension torques are summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA. Comparison between iMPS and mMPS conditions relative to \u003cem\u003eSES\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e revealed a significant main effect of stimulation (F(14, 153)\u0026thinsp;=\u0026thinsp;37.67, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η\u0026sup2;ₚ = 0.529). Post hoc pairwise comparisons using Dunnett\u0026rsquo;s test revealed all iMPS conditions (\u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e) (\u003cem\u003et\u003c/em\u003e(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) = -5.96 to -4.10, all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, all \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e = -3.66 to -0.27) and one mMPS condition (\u003cem\u003eVM\u003c/em\u003e) (\u003cem\u003et\u003c/em\u003e(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) = -3.95, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.001, \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e = -2.20) produced less knee extension torque than \u003cem\u003eSES\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e. Knee extension torque produced during single-muscle (\u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eVL\u003c/em\u003e) and paired-muscle (\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e, \u003cem\u003eRF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e) stimulation conditions did not differ significantly compared to \u003cem\u003eSES\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.10, \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e = -0.074 to 0.595). In contrast, \u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e produced greater torque than \u003cem\u003eSES\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e in 92% (11/12) of participants. Across all participants, \u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e yielded 50.8% (range: -17.5% to 208.6%) more knee extension torque compared to \u003cem\u003eSES\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e (mean: 33.3% MVC vs. 22.1% MVC; \u003cem\u003et\u003c/em\u003e(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e)\u0026thinsp;=\u0026thinsp;3.68, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.004, \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e = 1.06).\u003c/p\u003e\u003cp\u003eGroup data for normalized iMPS, mMPS, and \u003cem\u003eSES\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e mean peak knee flexion torques are summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB. Comparison between iMPS and mMPS conditions relative to \u003cem\u003eSES\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e revealed a significant main effect of stimulation (F(6,66)\u0026thinsp;=\u0026thinsp;7.839, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η\u0026sup2;ₚ = 0.416). Post hoc pairwise comparisons using Dunnett\u0026rsquo;s test revealed all iMPS conditions (\u003cem\u003eBF\u003c/em\u003e\u003csub\u003elh\u003c/sub\u003e, \u003cem\u003eBF\u003c/em\u003e\u003csub\u003esh\u003c/sub\u003e, \u003cem\u003eSM\u003c/em\u003e, \u003cem\u003eST\u003c/em\u003e) (t(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) = -7.80 to -4.94, all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.003, all \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e \u0026gt;1.03) and the \u003cem\u003eBF\u003c/em\u003e mMPS condition (t(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) = -4.137, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.009, \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e = 0.882) produced less knee flexion torque than \u003cem\u003eSES\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e. Knee flexion torque produced during all paired-muscle (\u003cem\u003eBF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eSM\u003c/em\u003e, \u003cem\u003eBF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eST\u003c/em\u003e, \u003cem\u003eSM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eST\u003c/em\u003e) mMPS conditions was not significantly different than \u003cem\u003eSES\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.054, \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e \u0026gt;0.502). Across all participants, \u003cem\u003eSES\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e produced greater knee flexion torque than \u003cem\u003eALL\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e (mean: 21.0% MVC vs. 18.4% MVC) in 42% (7/12) of participants; however, the group difference was not significant (t(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) = -0.741, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.933, \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e = 0.098).\u003c/p\u003e\n\u003ch3\u003eKnee torque between multiple motor point stimulation conditions\u003c/h3\u003e\n\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA summarizes the group data on normalized knee extension torques. Repeated measures ANOVA revealed a significant main effect of stimulation across quadricep mMPS conditions (F(6, 66)\u0026thinsp;=\u0026thinsp;27.247, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η\u0026sup2;ₚ = 0.712). Post hoc pairwise comparisons using Bonferroni correction indicated that all single-muscle conditions produced less torque than all paired-muscle and \u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e conditions (all t(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) \u0026lt; -1.078, all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.003, all \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e \u0026gt;0.802). \u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e produced significantly greater torque than all mMPS conditions (all \u003cem\u003et\u003c/em\u003e(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e)\u0026thinsp;\u0026gt;\u0026thinsp;4.40, all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.030, all \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e \u0026gt;0.67), except for the \u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e condition, which did not differ significantly (\u003cem\u003et\u003c/em\u003e(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e)\u0026thinsp;=\u0026thinsp;3.146, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.195, \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e = 0.429).\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB summarizes the group data on normalized knee flexion torque. Repeated measures ANOVA revealed a significant main effect on stimulation across hamstring mMPS conditions (F(6, 66)\u0026thinsp;=\u0026thinsp;7.838, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η\u0026sup2;ₚ = 0.416). Post hoc pairwise comparisons using Bonferroni correction indicated that two single-muscle (\u003cem\u003eSM\u003c/em\u003e and \u003cem\u003eST\u003c/em\u003e) conditions produced less torque than \u003cem\u003eALL\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e (both \u003cem\u003et\u003c/em\u003e(\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e)\u0026thinsp;\u0026gt;\u0026thinsp;4.10, both \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.026, both \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e \u0026gt;1.030). For paired-muscle mMPS conditions, \u003cem\u003eBF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eSM\u003c/em\u003e and \u003cem\u003eSM\u0026thinsp;+\u0026thinsp;ST\u003c/em\u003e produced less torque than \u003cem\u003eALL\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e (both t(\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e)\u0026thinsp;\u0026gt;\u0026thinsp;4.33, both \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.03; both \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e \u0026gt;0.289); however, \u003cem\u003eBF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eSM\u003c/em\u003e did not produce significantly different knee flexion torque than \u003cem\u003eALL\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e (t(\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e)\u0026thinsp;=\u0026thinsp;0.533, \u003cem\u003ep\u0026thinsp;=\u003c/em\u003e\u0026thinsp;1.000, \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e = 0.079).\u003c/p\u003e\n\u003ch3\u003eContribution of individual motor points to knee extension torque\u003c/h3\u003e\n\u003cp\u003eSummary data of coefficients for each quadriceps motor point are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The mixed-effects model indicated that all motor points contributed significantly to knee extension torque, except \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.438). The largest contributions were observed for \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e and \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, followed by \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, and \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, with \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e showing a smaller but significant effect. Participant-level variability was minimal (variance\u0026thinsp;=\u0026thinsp;0.003), suggesting consistent torque responses across individuals. These findings highlight the dominant roles of the vastus lateralis and rectus femoris motor points in torque generation.\u003c/p\u003e\n\u003ch3\u003eDifferences in observed and expected knee extension joint torque\u003c/h3\u003e\n\u003cp\u003eGroup data comparing τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e for all quadricep MPS combinations are found in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Paired \u003cem\u003et\u003c/em\u003e tests for single-muscle mMPS condition revealed no significant difference between τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e for \u003cem\u003eVM\u003c/em\u003e and \u003cem\u003eRF\u003c/em\u003e (all \u003cem\u003et\u003c/em\u003e(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) \u0026lt; -1.499, all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.059, all \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e \u0026lt; -0.609), whereas τ\u003csub\u003eobs\u003c/sub\u003e was significantly less than τ\u003csub\u003epre\u003c/sub\u003e for \u003cem\u003eVL\u003c/em\u003e (\u003cem\u003et\u003c/em\u003e(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) = -2.300, \u003cem\u003ep\u0026thinsp;=\u003c/em\u003e\u0026thinsp;0.042, \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e = -0.664). Repeated measures ANOVA was significant in the main effect on stimulation across τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e for \u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e (F(\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e)\u0026thinsp;=\u0026thinsp;5,459, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.001, η\u0026sup2;ₚ = 0.332), and \u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e (F(\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e)\u0026thinsp;=\u0026thinsp;4.827, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.003, η\u0026sup2;ₚ = 0.305), but no Dunnett post hoc revealed significant between any τ\u003csub\u003eobs\u003c/sub\u003e and all τ\u003csub\u003epre\u003c/sub\u003e (all \u003cem\u003et\u003c/em\u003e(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) \u0026lt; -1.602, all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.096, all \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e \u0026lt; -0.462). For \u003cem\u003eRF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e, there was a significant effect on stimulation across τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e (F(\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e)\u0026thinsp;=\u0026thinsp;11.746, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η\u0026sup2;ₚ = 0.516), with Dunnett post hoc revealing τ\u003csub\u003eobs\u003c/sub\u003e being significant less than all (4/4) τ\u003csub\u003epre\u003c/sub\u003e (all \u003cem\u003et\u003c/em\u003e(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) \u0026lt; -3.534, all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.009, all \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e \u0026lt; -1.020). Further, for \u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads,\u003c/sub\u003e there was a significant effect on stimulation across τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e (F(14, 154)\u0026thinsp;=\u0026thinsp;9.452, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η\u0026sup2;ₚ = 0.462), with Dunnett post hoc revealing τ\u003csub\u003eobs\u003c/sub\u003e being significant less than all (14/14) τ\u003csub\u003epre\u003c/sub\u003e (all \u003cem\u003et\u003c/em\u003e(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) \u0026lt; -2.919, all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05, all \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e \u0026lt; -0.636)\u003c/p\u003e\u003cp\u003eLinear regressions comparing τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e across mMPS conditions are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA, with metrics and alignment scores found in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. One-sample \u003cem\u003et\u003c/em\u003e tests of the regression slopes against unity indicated that slopes were generally less than 1, except for [\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e] (slope\u0026thinsp;=\u0026thinsp;0.990, \u003cem\u003et\u003c/em\u003e = -0.828, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.425, \u003cem\u003eR\u003c/em\u003e\u0026sup2; = 0.819, \u003cem\u003eRMSE\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.040, \u003cem\u003eF\u003c/em\u003e₁,ₙ₋₂ = 45.183) and [\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e] (slope\u0026thinsp;=\u0026thinsp;1.011, \u003cem\u003et\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.120, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.287, \u003cem\u003eR\u003c/em\u003e\u0026sup2; = 0.894, \u003cem\u003eRMSE\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.037, \u003cem\u003eF\u003c/em\u003e₁,ₙ₋₂ = 84.624), indicating that activation of both vastus medialis motor points offsets possible muscle activation overlap stemming from rectus femoris and vastus lateralis MPS. The distribution of slopes was right-skewed, indicating that most mMPS combinations underestimated observed torque relative to theoretical predictions (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB). In contrast, intercepts demonstrated an inverse pattern, with positive offsets becoming more prominent as slopes deviated below unity. This compensation effect was confirmed by a significant negative correlation between slopes and intercepts (\u003cem\u003er\u003c/em\u003e = -0.906, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001), suggesting that under-proportional scaling (slope\u0026thinsp;\u0026lt;\u0026thinsp;1) was systematically offset by upward shifts in the regression line (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB). Calculation of activation scores revealed that τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e comparisons involving \u003cem\u003eVM\u003c/em\u003e (i.e., stimulation for both vastus medialis motor points) had the best linear agreement, suggesting minimal intermuscular activation overlap, offsetting torque deviation attributed to vastus lateralis and rectus femoris (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eSummary of Linear Regression Slopes and Intercepts for Quadriceps mMPS τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e Comparisons\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eReference\u003c/p\u003e\u003cp\u003eNumber\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003emMPS\u003c/p\u003e\u003cp\u003eCondition\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eτ\u003csub\u003epre\u003c/sub\u003e\u003c/p\u003e\u003cp\u003eCombination\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSlope\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003eY-intercept\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eAlignment\u003c/p\u003e\u003cp\u003eScore\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e, \u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.011\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-0.021\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.032\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e, \u003cem\u003eRF\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.994\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-0.026\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.032\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e, \u003cem\u003eRF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;VL\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.966\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-0.008\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.042\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM, VL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.973\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-0.045\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.072\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL VM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.849\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.018\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.169\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.810\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.008\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.198\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e, \u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.740\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.022\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.262\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.751\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.042\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.291\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVL\u003c/em\u003e, \u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.688\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.031\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.343\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e, \u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.646\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.027\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.381\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.654\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.049\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.395\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVL\u003c/em\u003e, \u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.659\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.062\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.403\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.645\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.062\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.417\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.599\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.059\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.460\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eRF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.589\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.054\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.465\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eRF\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eRF\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.569\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.041\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.472\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.590\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.069\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.479\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.576\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.055\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.479\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.546\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.064\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.518\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.534\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.061\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.527\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.529\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.082\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.553\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.516\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.098\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.582\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.488\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.071\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.583\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.463\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.046\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.583\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eRF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.464\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.079\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.615\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eRF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.459\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.082\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.623\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.463\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.089\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.626\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.474\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.629\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eRF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.420\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.081\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.661\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe random forest regression model (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) demonstrated strong in-sample performance in predicting the mean quadricep TDI using observed values, achieving an \u003cem\u003eR\u003c/em\u003e\u0026sup2; of 0.958 and \u003cem\u003eRMSE\u003c/em\u003e of 0.020. However, when evaluated using 5-fold cross-validation, the model showed reduced generalizability, with an average \u003cem\u003eR\u003c/em\u003e\u0026sup2; of 0.509 and \u003cem\u003eRMSE\u003c/em\u003e of 0.057. Feature importance analysis revealed that rectus femoris MPS conditions (\u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e) were the strongest contributors to TDI variance, suggesting a dominant role of rectus femoris stimulation in driving deviations from linear torque summation. In contrast, vastus medialis MPS conditions (\u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM, VM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e) contributed the least, indicating a comparatively minor influence on TDI, resulting in better alignment between τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003eQuadriceps mMPS enhances knee extension torque output beyond SES\u003c/h2\u003e\u003cp\u003eStimulation of all quadriceps motor points produced\u0026thinsp;~\u0026thinsp;51% greater knee extension torque compared with conventional SES (33.3% MVC vs. 22.1% MVC) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). This finding shows that mMPS engages a broader portion of the quadriceps than \u003cem\u003eSES\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e, supporting its potential to improve orthotic performance and exercise-based neurorehabilitation applications. In particular, this enhancement could translate into improved outcomes for FES-cycling and FES-rowing, where torque production from the quadriceps is essential for generating sufficient power and sustaining aerobic workloads (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eOur results extend prior observations at the twitch level, where activating all quadriceps motor points yielded the largest summed torque, disproportionately driven by vastus lateralis (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e). Importantly, the present study demonstrates that this advantage persists under sustained tetanic stimulation, which more closely approximates the continuous activation required for functional movements. These findings also corroborate Gobbo et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e) who showed that a single motor point in tibialis anterior and vastus lateralis generated greater tetanic torque than SES, thereby reinforcing the generalizable superiority of motor point targeting across muscle groups.\u003c/p\u003e\u003cp\u003eFrom a mechanistic perspective, the greater torque observed with quadriceps mMPS likely reflects a broader and more distributed motor unit recruitment compared with \u003cem\u003eSES\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e. Single-electrode stimulation activates fibers predominantly beneath the electrode pair in a spatially fixed manner, whereas MPS exploits anatomically defined loci of excitability, enabling recruitment of motor axons that might otherwise remain inaccessible (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e). This mechanism is supported by neurophysiological evidence that SES stimulates a restricted subset of the muscle compared with voluntary activation or peripheral nerve stimulation (\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). Thus, mMPS may more closely approximate physiological recruitment patterns and generate stronger contractions.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eMotor point contributions within the quadriceps\u003c/h3\u003e\n\u003cp\u003eThe present study identified the proximal and intermediate vastus lateralis motor points (\u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e) as the dominant contributors to knee extension torque, consistent with the structural and physiological prominence of the vastus lateralis (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Anatomical and imaging studies have shown that the vastus lateralis accounts for the largest proportion of quadriceps strength (~\u0026thinsp;40%) compared with the vastus medialis (~\u0026thinsp;25%) and rectus femoris\u0026ndash;vastus intermedius (~\u0026thinsp;35%) (\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e). This regional dominance likely explains the disproportionately high knee extension torque observed when stimulating \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e and \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e. In contrast, the vastus medialis contributed more modest absolute torque (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), which may reflect its smaller cross-sectional area and more oblique fiber orientation (\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e). Nevertheless, inclusion of vastus medialis motor points consistently enhanced torque generation with minimal redundancy. Its anatomical compartmentalization allows it to activate regions under-recruited by \u003cem\u003eSES\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e), complementing the vastus lateralis and improving overall recruitment heterogeneity. This supports the functional importance of \u003cem\u003eVM\u003c/em\u003e inclusion despite its smaller individual contribution (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e). Rectus femoris, by comparison, contributed inconsistently to torque output, with variable effects (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) Given its biarticular structure and smaller proportional role in knee extension, rectus femoris appears to be a less reliable contributor compared with the vastus lateralis and medialis (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eCollectively, these findings align with prior reports that MPS achieves more complete muscle activation than SES, which often under-recruits regions such as the vastus medialis and lateralis (\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e). By optimizing motor point selection, stimulation can engage a broader and more efficient portion of the quadriceps compared with conventional SES, supporting both orthotic performance and potential therapeutic benefits.\u003c/p\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eRecruitment overlap within the quadriceps\u003c/h2\u003e\u003cp\u003eA secondary aim of this study was to assess recruitment overlap by comparing observed torque with linear predictions from individual motor point contributions. This analysis provides insight into the efficiency of channel allocation \u0026ndash; whether additional stimulation sites uniquely increase torque or simply activate fibers already recruited by other sites.\u003c/p\u003e\u003cp\u003eThe largest discrepancies between observed and predicted torques were observed with rectus femoris stimulation, indicating substantial overlap (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). This may stem from current spread into neighboring quadriceps motor point domains or complex intertendinous coupling between quadriceps heads and the quadriceps tendon (\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e), which may contribute to redundant torque output Such overlap reduces the efficiency of stimulation, as additional channels contribute less unique torque relative to their cost in complexity and participant burden. In contrast, vastus medialis stimulation was associated with minimal redundancy, suggesting that it engages a relatively distinct pool of motor units not accessed by vastus lateralis or rectus femoris stimulation.\u003c/p\u003e\u003cp\u003eThese findings carry practical implications. When optimizing channel allocation for MPS, priority should be given to motor point sites that both contribute significant torque and minimize overlap \u0026ndash; namely proximal and intermediate vastus lateralis, together with vastus medialis. Rectus femoris stimulation should be considered only when additional channels are available and when its incremental torque benefits outweigh the cost of redundancy. Such a selective approach aligns with recommendations from prior work emphasizing that maximizing efficiency is as important as maximizing torque when designing mMPS stimulation protocols (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eHamstrings response to mMPS\u003c/h2\u003e\u003cp\u003eIn contrast to the quadriceps, stimulation of all hamstring motor points did not significantly increase knee flexion torque relative to SES (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). This limited effect likely reflects both physiological and methodological constraints. Motor point mapping has demonstrated that the hamstrings possess fewer and more variably located sites compared to the quadriceps (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e), with deeper locations of the semimembranosus and biceps femoris short head requiring higher stimulation currents for motor point identification in the present study, suggesting less accessible access using transcutaneous stimulation. This may have limited the torque-generating potential of these sites before participant tolerance was reached. Further, in the current study, participants were seated such that the stimulating electrodes were compressed between the seating surface and the skin, which may have altered electrode-tissue contact. Additionally, deformation of the underlying hamstrings could have influenced current distribution, thereby affecting the effective stimulation delivered to the muscle in both MPS and \u003cem\u003eSES\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e conditions, limiting knee flexion torque production from both FES methods.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eLimitations\u003c/h2\u003e\u003cp\u003eSeveral limitations should be acknowledged. First, the present study was conducted in neurologically intact participants, and it remains uncertain whether the same torque gains and recruitment patterns would generalize to individuals with neurological impairments, where muscle atrophy, spasticity, and altered excitability may influence outcomes (\u003cspan additionalcitationids=\"CR28\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e). Second, we used a finite number of surface electrodes, which constrained the spatial resolution of motor point targeting. Although we attempted to identify and stimulate all accessible motor points, deeper sites or those with high interindividual variability may have been missed (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e). Third, we evaluated tetanic contractions under isometric conditions, which may not fully capture the dynamic demands of functional FES applications such as cycling, walking, or standing. Finally, we normalized torque to maximal voluntary contraction, which provides a useful benchmark in neurologically intact participants but may not directly translate to clinical populations with impaired voluntary control.\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThis study demonstrates that stimulation of all quadriceps motor points generated 51% greater torque compared with conventional SES, highlighting the potential of mMPS to improve the effectiveness of FES interventions. Second, the largest torque contributions were derived from proximal and intermediate vastus lateralis sites, together with vastus medialis, indicating that these should be prioritized for optimized motor point selection. Third, rectus femoris stimulation produced torque but also introduced substantial overlap, suggesting it should be considered only when channel allocation permits and when the torque benefit outweighs redundancy. In contrast, stimulation of all hamstring motor points did not yield additional torque, highlighting muscle-specific constraints. These findings provide practical guidance for electrode placement and channel allocation, suggesting that optimal quadriceps stimulation can be achieved by prioritizing a limited subset of motor points. Taken together, they establish a framework for refining FES strategies to maximize torque generation, minimize redundancy, and ultimately improve functional outcomes in neurorehabilitation.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\u003ch2\u003eParticipants\u003c/h2\u003e\u003cp\u003eTwelve neurologically intact participants (9 males, 3 females; age: 25.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3 yrs, body mass: 72.3\u0026thinsp;\u0026plusmn;\u0026thinsp;15.3 kg, height: 175.8\u0026thinsp;\u0026plusmn;\u0026thinsp;6.7 cm) took part in this study. All participants self-reported no peripheral or central neuromuscular, osteological, or cardiovascular conditions. To avoid any confounding effects from fatigue or delayed-onset muscle soreness on artificially- or voluntarily induced muscle contractions, participants were asked to abstain from any intensive exercise of the lower limbs a minimum of 48 hours prior to undergoing experimental procedures. All participants provided written and verbal informed consent prior to participation. The experimental procedures were approved by the Institutional Research Ethics Board.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003eMotor point identification\u003c/h2\u003e\u003cp\u003ePrior to experimental procedures, motor points for the right anterior and posterior thigh were identified. In total, up to seven and four motor points were expected to be identified for the quadriceps femoris and for the biceps femoris, respectively (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e). To account for interindividual differences in motor point positions (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e), locations were initially estimated using bony and soft tissue anatomical landmarks and confirmed by tracking the skin with a cathodic pen electrode (contact surface: 2 mm\u003csup\u003e2\u003c/sup\u003e) (Chattanooga Physio, DJO Global, Chattanooga, TN, United States) delivering a low-intensity (\u0026lt;\u0026thinsp;15 mA) pulse at 2 Hz. The corresponding anode (5 cm x 10 cm; Axelgaard Manufacturing Co. Ltd., Fallbrook, CA, United States) was centered about the antagonist group. Motor points were tracked and their locations confirmed through manual palpation of the surrounding musculature and visual inspection of the largest skin deformation from muscle contracture in response to the smallest delivered electrical current (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e). All quadriceps motor points were identified on the right thigh with the participant positioned in 80\u0026deg; of hip flexion and 90\u0026deg; of knee flexion (anatomical position\u0026thinsp;=\u0026thinsp;0\u0026deg;), as measured relative to the anatomical axes of rotation using an analog goniometer. Up to seven motor points were located for the superficial quadriceps femoris muscles: two for the vastus medialis (distal, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e; and proximal, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e), two for the rectus femoris (distal, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e; and proximal, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e), and three for the vastus lateralis (distal, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e; intermediate, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e; and proximal, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e) (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e). For hamstring motor point identification, participants were positioned prone with the knee flexed to 70\u0026deg; relative to full extension (0\u0026deg;). Up to four motor points were located: two for the biceps femoris (long head, \u003cem\u003eBF\u003c/em\u003e\u003csub\u003elh\u003c/sub\u003e; and short head, \u003cem\u003eBF\u003c/em\u003e\u003csub\u003esh\u003c/sub\u003e), one for the semimembranosus (\u003cem\u003eSM\u003c/em\u003e), and one for the semitendinosus (\u003cem\u003eST\u003c/em\u003e) (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e). All motor points were marked on the skin using indelible ink. Motor point locations for all quadriceps (seven total) and hamstrings (four total) muscles were identified for 12/12 participants.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003eStimulating electrode placements: quadriceps configuration\u003c/h2\u003e\u003cp\u003ePrior to surface electrode fixation, the skin was cleaned using alcohol swabs (70% v/v), being carful not to remove the motor point markings. For the MPS conditions, individual self-adhesive cathode-anode electrode pairs (two 5 x 5 cm) were adopted for each motor point (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). The cathode was centered over the motor point, while the anode was positioned, in parallel, either slightly proximal or distal to the cathode over the respective muscle. An edge-to-edge interelectrode distance of approximately 2 cm was aimed for; however, this spacing was not always feasible due to limited surface area on the thigh, particularly without encroaching on the adductor or hamstring muscle groups. In total, seven cathode-anode pairs were adopted (14 total electrodes). For the quadricep SES (\u003cem\u003eSES\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e) condition across the anterior thigh, a large self-adhesive electrode pair (7.5 cm \u0026times; 10 cm) was placed in a proximal-distal configuration (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). The proximal cathode was oriented transversely, with its superior margin positioned approximately 10 cm distal to the inguinal groove and slightly lateral, positioned over the proximal bodies of the vastus lateralis and rectus femoris muscles, while avoiding the femoral triangle. The distal anode was also oriented transversely, with the inferior margin positioned approximately 5 cm proximal to the base of the patella (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). To minimize potential bias in experimenter placement of \u003cem\u003eSES\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e electrodes relative to participants\u0026rsquo; motor points, markings indicating motor point locations were erased using rubbing alcohol until no visible pigment remained. These motor point locations were not referenced during \u003cem\u003eSES\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e electrode placement.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003eStimulating electrode placements: hamstrings configuration\u003c/h2\u003e\u003cp\u003eFor the MPS condition, individual cathode-anode electrode pairs (5 \u0026times; 5 cm each) were assigned to each motor point (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). As the hamstring muscles are biarticular that feature a pelvic origin, changes in hip angle can lengthen their muscle fibers (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e), which may inadvertently migrate the motor point relative to the joint angle they were initially searched for (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e). To account for potential superior motor point migration due to differences in hip angle between motor point screening (anatomically neutral) and experimental evaluation (80\u0026deg; flexion) in the present study, the cathode was centered approximately 1 cm superior to the identified motor point and aligned to follow the respective muscle fiber orientation as closely as possible. The anode was positioned either proximally or distally along the same muscle, based on available space. In total, four cathode-anode pairs were adopted (eight total electrodes). For the hamstring SES (\u003cem\u003eSES\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e) condition across the posterior thigh, a large (7.5 cm \u0026times; 10 cm) cathode-anode pair was positioned proximally and distally (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). The proximal cathode was oriented transversely, immediately distal to the inferior gluteal fold along the midline of the thigh. The distal anode was also oriented transversely, with its inferior margin positioned approximately 3 cm superior to the center of popliteal fossa, superimposing the surface impressions of the distal hamstring tendons. Markings denoting motor point locations were erased and not considered when positioning the \u003cem\u003eSES\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e electrodes.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e\u003ch2\u003ePre-experimental interventions\u003c/h2\u003e\u003cp\u003eIn order to evaluate artificially induced knee extension and knee flexion isometric tetanic torques induced from FES (MPS and SES) of the thigh, participants were comfortably seated with their right knee joint aligned with the center of rotation of a joint dynamometer (Biodex System 3, Biodex Medical Inc., Shirly, NY, United States). For quadricep FES conditions, the hip was flexed at 80\u0026deg; and knee flexed at 90\u0026deg; (anatomical position\u0026thinsp;=\u0026thinsp;0\u0026deg; reference) in order to position the quadriceps in an advantageous muscle length to evoke larger torques (\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e). For hamstring FES conditions, the hip was flexed at 80\u0026deg; and knee flexed 70\u0026deg;. Inelastic cushioned restraints were applied across the torso and thigh to stabilize the body and mitigate any extraneous joint motion that might confound the assessment of knee torque output during experimental procedures. The leg was secured to the dynamometer attachment arm with a cushioned restraint positioned above the ankle joint, with the foot allowed to hang freely. To enable interindividual comparisons of FES-induced knee torque, participants performed two maximal voluntary contractions (MVCs) of knee extension and flexion for 5 seconds, with strong verbal encouragement, each separated by a 1-minute rest. Participants were instructed to \u0026lsquo;contract as strong and as fast as possible\u0026rsquo; while minimizing hip involvement, ensuring that the movement was isolated to knee extension and flexion. Real-time torque traces were displayed on a computer monitor to participants to facilitate maximal effort during contractions. The average maximal knee torque from the steady-state torque profile across both MVC trials was used to normalize all FES-induced torque values.\u003c/p\u003e\u003cp\u003eTo establish the current amplitude for FES conditions, the maximal tolerable stimulation intensity (MTSI) was individually determined for each individual motor point and SES electrode configurations and subsequently used for experimental evaluations. A designated neuromuscular electrical stimulation device (Chattanooga Continuum, Wilmington, DE, United States) delivered an asymmetric, charge-balanced cathodic waveform (50 Hz frequency, 400 \u0026micro;s pulse width) for all FES sites. Stimulation was manually triggered and carefully controlled by the experimenter using an external push button. The MTSI for each FES site was determined by gradually increasing stimulation from 5 mA in 5 mA steps, applied for 3 s at each increment, until the participant\u0026rsquo;s tolerance threshold was reached. The intensity was then adjusted in \u0026plusmn;\u0026thinsp;1 mA increments to precisely establish the MTSI. The experimenter continually assessed the participant's ability and willingness to tolerate higher currents before increasing the stimulation intensity. To limit transient fatigue and discomfort from influencing stimulation tolerance, FES conditions were conducted in a pseudorandom order, ensuring that motor points from the same muscle were not evaluated in immediate succession. Participants were instructed to consider the determination of the MTSI at each FES site independently, without using the sensations from other sites to influence their judgment for another. For the successful application of the final MTSI in experimental testing, the following criteria had to be met: (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) the MTSI induced a fused, nonfasciculated muscle state (visually confirmed), in which a steady-state torque profile was registered; (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) no exogenous joint movement, either voluntary or FES-induced, was observed, as confirmed through visual inspection and manual palpation of adjacent or antagonistic muscles (e.g., flexion/extension of the torso, hamstring contraction during quadriceps stimulation, quadriceps contraction during hamstring stimulation); and (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) the stimulation amplitude was tolerated by the participant. If exogenous joint movement was visually observed (e.g., hip extension/flexion), the stimulation intensity was finely adjusted about the MTSI until only extension (quadricep FES) or flexion (hamstring FES) of the knee was produced, with minimal adjacent joint movement. If all criteria were satisfied, the designated current was recorded for each FES site and were adopted for all experimental conditions thereafter. In the current study, two participants reached the maximal stimulator output (100 mA) for several motor points, which was then adopted for testing. Consequently, it remains uncertain whether the final 100 mA represented their true tolerations for those sites.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e\u003ch2\u003eExperimental procedures\u003c/h2\u003e\u003cp\u003eTo evaluate the potential of FES-induced tetanic torque production at the motor points of the thigh, \u0026lsquo;individual MPS\u0026rsquo; (i.e., direct stimulation of each motor point separately, iMPS), and inter- and intramuscular \u0026lsquo;multiple MPS\u0026rsquo; (i.e., direct stimulation of more than one motor point, mMPS) conditions were assessed. The theoretical number of motor point combinations for the quadriceps and hamstrings are 127 (2⁷ \u0026ndash; 1) and 15 (2⁴ \u0026ndash; 1), respectively. However, practical limitations \u0026ndash; including testing duration, FES-induced muscle fatigue, and participant burden \u0026ndash;made it infeasible to evaluate all possible tetanic stimulation combinations within a single session, particularly given day-to-day variations in tolerance and performance across sex and session number (\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e). Therefore, to evaluate the tetanic torque-generating potential of mMPS, we restricted our analysis to muscle-specific motor point configurations. This included stimulation of individual motor points, all motor points within a single muscle, paired muscles, and compartmental activation. This framework enabled investigation of torque recruitment dynamics in response to mMPS.\u003c/p\u003e\u003cp\u003eFor the quadriceps, 13 total MPS conditions were evaluated, comprising both iMPS and mMPS protocols. The iMPS conditions involved the independent stimulation of the seven motor points (\u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e). The mMPS conditions included: (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) single-muscle MPS, defined as the simultaneous stimulation of all motor points within a single muscle (e.g., \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e and \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e for vastus medialis), for a total of three conditions (\u003cem\u003eVM\u003c/em\u003e, \u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eVL\u003c/em\u003e); (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) paired-muscle MPS, defined as the simultaneous stimulation of all motor points from two muscles (e.g., \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, and \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e for vastus medialis and rectus femoris), for a total of three conditions (\u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e, \u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e, \u003cem\u003eRF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eVL\u003c/em\u003e); and (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) \u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e MPS, involving the simultaneous stimulation of all seven quadriceps motor points, comprising one condition.\u003c/p\u003e\u003cp\u003eFor the hamstrings, nine total MPS conditions were evaluated, consisting of both iMPS and mMPS protocols. The iMPS conditions involved the independent stimulation of four single motor points (\u003cem\u003eBF\u003c/em\u003e\u003csub\u003elh\u003c/sub\u003e, \u003cem\u003eBF\u003c/em\u003e\u003csub\u003esh\u003c/sub\u003e \u003cem\u003eSM\u003c/em\u003e, \u003cem\u003eST\u003c/em\u003e). The mMPS conditions included: (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) single-muscle MPS, for a total of three conditions; here, only the biceps femoris contained more than one motor point, yielding one condition. Because semimembranosus and semitendinosus each have only one motor point (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e), their evaluations were categorized under single-muscle MPS rather than iMPS; (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) paired-muscle MPS, for a total of three conditions (\u003cem\u003eBF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eSM\u003c/em\u003e, \u003cem\u003eBF\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eST\u003c/em\u003e, \u003cem\u003eSM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eST\u003c/em\u003e); and (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) \u003cem\u003eALL\u003c/em\u003e\u003csub\u003ehams\u003c/sub\u003e MPS, comprising one condition.\u003c/p\u003e\u003cp\u003eThe iMPS conditions were administered in a block-randomized order, with the constraint that no two motor points from the same muscle were tested consecutively. For the mMPS conditions, stimulation began with single-muscle MPS, followed by paired-muscle MPS (randomized within their respective block), and concluded with stimulating all motor points. To minimize fatigue-related bias, single-muscle MPS was tested before paired-muscle MPS. This sequence was chosen to reduce the risk of underestimating knee torque due to potential fatigue carry-over from conditions involving a greater number of stimulated motor points. The overall sequence \u0026ndash; iMPS followed by mMPS \u0026ndash; was kept consistent across all participants to ensure standardization. Each FES condition consisted of two continuous stimulation trials, delivered using a 1:2:1 stimulation duty cycle: 6 seconds of stimulation, followed by 12 seconds of rest (no voluntary or FES-induced contractions), and then another 6 seconds of stimulation (total condition duration\u0026thinsp;=\u0026thinsp;24 seconds), resulting in two submaximal steady-state torque outputs (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC). This stimulation protocol was standardized across all quadriceps and hamstring locations for iMPS, mMPS, and SES conditions. A 2-minute rest period was provided between each FES condition. After completing all MPS conditions, the same stimulation sequence was applied using the respective SES configuration. All quadriceps FES trials were completed first, followed by all hamstring trials, with a minimum 5-minute rest period separating the two muscle groups. Following all respective quadriceps MPS and hamstring MPS conditions, one final MVC (\u003cem\u003eMVC\u003c/em\u003e\u003csub\u003epost\u003c/sub\u003e) was performed for knee extension and knee flexion and compared to \u003cem\u003eMVC\u003c/em\u003e\u003csub\u003epre\u003c/sub\u003e to assess whether fatiguing effects took place over the course of the experimental session.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec22\" class=\"Section2\"\u003e\u003ch2\u003eData collection and analysis\u003c/h2\u003e\u003cp\u003eAll participant knee torque data were collected using LabChart software (LabChart Pro Modules 2018, version 8). Knee torque signals (N\u0026middot;m) were recorded and sampled at 2000 Hz using a 12-bit analog-to-digital data acquisition system (PowerLab System 16/30, ADInstruments, Bella Vista, Australia). Evoked knee torque was evaluated by identifying the peak torque within a 3- to 4-second window of steady-state output, and then geometrically averaging these values from both 6-second contractions for each FES condition. All mean knee torque values were normalized to each participant\u0026rsquo;s mean preintervention MVC (\u003cem\u003eMVC\u003c/em\u003e\u003csub\u003epre\u003c/sub\u003e) and expressed as a percentage (% MVC) to be used for group comparisons.\u003c/p\u003e\u003cp\u003eTo estimate the contribution of individual quadriceps motor points to knee extension torque, we fitted a linear mixed-effects model with normalized knee extension torque (% MVC) as the dependent variable. The seven quadricep motor points (\u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, \u003cem\u003eVL\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e) were entered as binary fixed effects (1\u0026thinsp;=\u0026thinsp;activated, 0\u0026thinsp;=\u0026thinsp;not), and participant was included as a random intercept to account for repeated measures. Model coefficients were interpreted as average motor point contributions conditional on the others, with 95% confidence intervals reported. For presentation, coefficients were expressed as percentage contributions by dividing each motor point coefficient by the sum of all motor point coefficients plus the intercept and multiplying by 100.\u003c/p\u003e\u003cp\u003ePrevious studies have reported discrepancies between observed torque (τ\u003csub\u003eobs\u003c/sub\u003e) from artificially-induced contractions and the theoretically predicted torque (τ\u003csub\u003epre\u003c/sub\u003e) when multiple quadricep motor points were simultaneously activated (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e). In the current study, under the assumption that FES selectively and independently recruits nonoverlapping muscle subdomains during continuous delivery, knee extension torque output from iMPS and mMPS quadricep conditions was compared against τ\u003csub\u003epre\u003c/sub\u003e defined as the linear sum of τ\u003csub\u003eobs\u003c/sub\u003e from any combination of conditions activating the same set of motor points as the target mMPS condition. Each stimulation condition \u0026ndash; whether targeting an individual motor point, single-muscle, paired-muscle, or all motor points \u0026ndash; was encoded in a binary activation matrix \u003cb\u003eA\u003c/b\u003e \u0026isin; {0,1}\u003csup\u003e\u003cem\u003em\u003c/em\u003ex\u003cem\u003en\u003c/em\u003e\u003c/sup\u003e, where \u003cem\u003em\u003c/em\u003e is the total number of stimulation conditions (including both iMPS and mMPS) and \u003cem\u003en\u003c/em\u003e is the number of topographically distinct quadricep motor points (7 total). Each row of \u003cb\u003eA\u003c/b\u003e corresponds to a stimulation condition, and each column indicates whether a specific motor point was activated (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) or not (0). For a given composite stimulation condition \u003cem\u003ei\u003c/em\u003e, all possible subsets \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e \u0026sube; {1,\u0026hellip;, \u003cem\u003em\u003c/em\u003e} of stimulation conditions were generated such that their combined motor point activations exactly matched those of condition \u003cem\u003ei\u003c/em\u003e, without double-counting any motor point. This constraint can be expressed as:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\left(1\\right)\\:\\:\\sum\\:_{j=1}^{n}{A}_{ij}=\\:\\sum\\:_{k\\in\\:{C}_{i}}\\sum\\:_{j=1}^{n}{A}_{kj}\\:\\left(2\\right)\\:\\:\\sum\\:_{k\\in\\:{C}_{i}}{A}_{kj\\:}\\le\\:1\\:\\:\\forall\\:j=1,\\:\\dots\\:,\\:n$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eHere, Eq.\u0026nbsp;(1) ensures that the combined stimulation conditions activate exactly the same number of motor points as the composite condition \u003cem\u003ei\u003c/em\u003e. Eq.\u0026nbsp;(2) prevents any motor point from being counted more than once when summing MPS conditions, thereby avoiding double-counting motor points. The τ\u003csub\u003epre\u003c/sub\u003e for condition \u003cem\u003ei\u003c/em\u003e was then calculated as the sum of τ\u003csub\u003eobs\u003c/sub\u003e, such that:\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:{\\tau\\:}_{\\text{pre}}^{\\left(i\\right)}={\\sum\\:}_{k\\in\\:{C}_{i}}{\\tau\\:}_{\\text{obs}}^{\\left(k\\right)}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eAs an example, consider the mMPS condition \u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e, which simultaneously activates four distinct motor points: \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, \u003cem\u003eVM\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, and \u003cem\u003eRF\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e. The τ\u003csub\u003epre\u003c/sub\u003e for this condition, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{\\text{pre}}^{\\left(\\text{VM}\\text{+}\\text{RF}\\right)}\\)\u003c/span\u003e\u003c/span\u003e, was estimated by summing τ\u003csub\u003eobs\u003c/sub\u003e from all valid subsets of conditions whose combined motor point activations were topographically equivalent with respect to \u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e. Specifically, four distinct combinations are possible from the combination of individual, single-muscle, and paired-muscle MPS conditions evaluated in the current study:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eall relevant iMPS conditions:\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:{\\tau\\:}_{\\text{pre}}^{\\left(\\text{VM}\\text{+}\\text{RF}\\right)}={\\tau\\:}_{\\text{obs}}^{\\left({\\text{VM}}_{\\text{p}}\\right)}+{\\tau\\:}_{\\text{obs}}^{\\left({\\text{VM}}_{\\text{d}}\\right)}+{\\tau\\:}_{\\text{obs}}^{\\left({\\text{RF}}_{\\text{p}}\\right)}+{\\tau\\:}_{\\text{obs}}^{\\left({\\text{RF}}_{\\text{d}}\\right)}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003esingle-muscle \u003cem\u003eVM\u003c/em\u003e mMPS and rectus femoris iMPSs:\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$$\\:{\\tau\\:}_{\\text{pre}}^{\\left(\\text{VM}\\text{+}\\text{RF}\\right)}={\\tau\\:}_{\\text{obs}}^{\\left(\\text{VM}\\right)}+{\\tau\\:}_{\\text{obs}}^{\\left({\\text{RF}}_{\\text{p}}\\right)}+{\\tau\\:}_{\\text{obs}}^{\\left({\\text{RF}}_{\\text{d}}\\right)}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003esingle-muscle \u003cem\u003eRF\u003c/em\u003e mMPS and vastus medialis iMPSs:\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003cdiv id=\"Eque\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Eque\" name=\"EquationSource\"\u003e\n$$\\:{\\tau\\:}_{\\text{pre}}^{\\left(\\text{VM}\\text{+}\\text{RF}\\right)}={\\tau\\:}_{\\text{obs}}^{\\left(\\text{RF}\\right)}+{\\tau\\:}_{\\text{obs}}^{\\left({\\text{VM}}_{\\text{p}}\\right)}+{\\tau\\:}_{\\text{obs}}^{\\left({\\text{VM}}_{\\text{d}}\\right)}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003esingle-muscle \u003cem\u003eVM\u003c/em\u003e and \u003cem\u003eRF\u003c/em\u003e mMPSs:\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003cdiv id=\"Equf\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equf\" name=\"EquationSource\"\u003e\n$$\\:{\\tau\\:}_{\\text{pre}}^{\\left(\\text{VM}\\text{+}\\text{RF}\\right)}={\\tau\\:}_{\\text{obs}}^{\\left(\\text{VM}\\right)}+{\\tau\\:}_{\\text{obs}}^{\\left(\\text{RF}\\right)}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eEach combination satisfies the constraint that all motor points activated during the \u003cem\u003eVM\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eRF\u003c/em\u003e stimulation are represented exactly once, with no redundancy across constituent subsets. This procedure was applied across all mMPS conditions to generate corresponding τ\u003csub\u003epre\u003c/sub\u003e estimates for comparison against the respective experimentally measured τ\u003csub\u003eobs\u003c/sub\u003e values. In total, 29 τ\u003csub\u003epre\u003c/sub\u003e combinations were evaluated for the quadriceps, comprising:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e3 for single-muscle MPS (3 condition x 1 τ\u003csub\u003epre\u003c/sub\u003e, each);\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e12 for paired-muscle MPS (3 conditions x 4 τ\u003csub\u003epre,\u003c/sub\u003e each), and;\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e14 for \u0026lsquo;all motor point\u0026rsquo; stimulation (1 condition x 14 τ\u003csub\u003epre\u003c/sub\u003e)\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eNext, to quantify the deviation between τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e, a torque discrepancy index (TDI) was calculated for each pair of τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e, such that \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:TDI\\:=\\:1-\\frac{{\\tau\\:}_{\\text{pre}}^{\\left(i\\right)}}{{\\tau\\:}_{\\text{obs}}^{\\left(i\\right)}}\\)\u003c/span\u003e\u003c/span\u003e, where values closer to zero indicate stronger agreement between τ\u003csub\u003eobs\u003c/sub\u003e and predicted linear sums (τ\u003csub\u003epre\u003c/sub\u003e). The TDI was used as a proxy to quantify discrepancies between τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e, attributed to potential activation overlap from FES and/or mechanical interactions arising from unique muscle geometries and properties. To explore the discrepancy between τ\u003csub\u003eobs\u003c/sub\u003e and τ\u003csub\u003epre\u003c/sub\u003e, a machine learning approach was used to assess the relative contribution of each stimulation condition (including iMPS and mMPS conditions) for the quadriceps. Torque discrepancy index values were used to train a random forest regression model (100 estimators, random state = 42) based on one-hot encoded representations of each stimulation condition. Each MPS combination was decomposed into its constituent MPS condition, forming a binary feature matrix, and the model was trained to predict the mean normalized TDI associated with each combination. To ensure generalizability, 5-fold cross-validation was performed. Feature importance scores were extracted from the trained model to identify the MPS conditions most strongly driving TDI, thereby providing insight into the contributions underlying deviations from linear torque summation. Additionally, to evaluate the agreement between τ\u003csub\u003epre\u003c/sub\u003e and τ\u003csub\u003eobs\u003c/sub\u003e torque responses, linear regression models were fitted for each quadricep mMPS combination. From each regression, the slope and y-intercept were extracted and compared against the ideal case of slope = 1 (perfect proportionality) and intercept = 0 (no systematic offset). To provide a single quantitative measure of agreement, we calculated an alignment score, defined as the Euclidean distance from the optimal point (slope = 1, intercept = 0):\u003cdiv id=\"Equg\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equg\" name=\"EquationSource\"\u003e\n$$\\:\\text{A}\\text{l}\\text{i}\\text{g}\\text{n}\\text{m}\\text{e}\\text{n}\\text{t}\\:\\text{S}\\text{c}\\text{o}\\text{r}\\text{e}\\:=\\:\\sqrt{{\\left(slope\\:-\\:1\\right)}^{2}+\\:{\\left(Y-intercept\\right)}^{2}}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThis metric integrates both proportional accuracy (slope) and systematic bias (intercept), with lower values reflecting closer alignment between τ\u003csub\u003epre\u003c/sub\u003e and τ\u003csub\u003eobs\u003c/sub\u003e. In this framework, mMPS combinations with the smallest alignment scores were interpreted as providing better linear alignment between τ\u003csub\u003epre\u003c/sub\u003e and τ\u003csub\u003eobs\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003eWe estimated additive motor point contributions with a linear mixed-effects model. Linear agreement between τ\u003csub\u003epre\u003c/sub\u003e and τ\u003csub\u003eobs\u003c/sub\u003e was assessed via simple regression (slope, intercept, alignment score), and factors associated with TDI were examined using a random forest regressor with 5-fold cross-validation.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec23\" class=\"Section2\"\u003e\u003ch2\u003eStatistical analysis\u003c/h2\u003e\u003cp\u003ePrior to statistical analysis, neuromechanical data were assessed for normality using the Shapiro\u0026ndash;Wilk test, with appropriate parametric or nonparametric tests subsequently applied. To evaluate whether participant fatigue occurred as a result of the experimental interventions, a paired-samples \u003cem\u003et\u003c/em\u003e test was used to compare pre- and postexperimental MVC values (\u003cem\u003eMVC\u003c/em\u003eₚ\u003csub\u003er\u003c/sub\u003eₑ vs. \u003cem\u003eMVC\u003c/em\u003eₚₒₛₜ). These normalized torques were analyzed separately for knee extension and knee flexion.\u003c/p\u003e\u003cp\u003ePrior to all repeated-measures analyses of variance (ANOVA), the assumption of sphericity was assessed using Mauchly\u0026rsquo;s test. When sphericity was violated, Greenhouse-Geisser corrections were applied to adjust the degrees of freedom accordingly. To compare torque outputs between mMPS and conventional SES, separate repeated-measures ANOVAs with Dunnett-adjusted post hoc comparisons were conducted for the quadriceps and hamstrings. These analyses evaluated differences in normalized peak knee torque across 13 quadriceps MPS conditions (seven iMPS and six mMPS) and eight hamstring MPS conditions (four iMPS and four mMPS), with each condition compared to its respective SES control. To further assess differences among the mMPS conditions, additional repeated-measures ANOVAs with Bonferroni-adjusted pairwise comparisons were performed separately for each muscle group. This two-tiered analytic approach was implemented to preserve statistical power while appropriately controlling for multiple comparisons. Conducting a single omnibus ANOVA with all possible pairwise comparisons (105 for quadriceps, 45 for hamstrings) would have substantially inflated the risk of Type I error and reduced the sensitivity to detect meaningful effects.\u003c/p\u003e\u003cp\u003eObserved and predicted torques were compared to assess the degree of nonlinearity in torque summation and the relative contribution of mMPS conditions to gauge activation overlaps. For single-muscle mMPS conditions, which each comprised only one τₚ\u003csub\u003er\u003c/sub\u003eₑ condition, paired \u003cem\u003et\u003c/em\u003e tests were performed comparing their respective τ\u003csub\u003eobs\u003c/sub\u003e and τₚ\u003csub\u003er\u003c/sub\u003eₑ. For paired-muscle and \u003cem\u003eALL\u003c/em\u003e\u003csub\u003equads\u003c/sub\u003e mMPS conditions, repeated-measures ANOVA was conducted to assess whether τₚ\u003csub\u003er\u003c/sub\u003eₑ combinations significantly differed from the corresponding τ\u003csub\u003eobs\u003c/sub\u003e, with Dunnett post hoc tests used to compare each τₚ\u003csub\u003er\u003c/sub\u003eₑ combination directly against its respective τ\u003csub\u003eobs\u003c/sub\u003e. Linear regression models were fitted for each τₚ\u003csub\u003er\u003c/sub\u003eₑ against τ\u003csub\u003eobs\u003c/sub\u003e using a leave-one-out approach, where each data point was sequentially omitted and the slope recalculated. Slope coefficients were tested against 1 to evaluate proportional agreement, and y-intercepts were examined for systematic offsets. Model performance was further quantified using \u003cem\u003eR\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e, indicating the proportion of variance in τ\u003csub\u003eobs\u003c/sub\u003e explained by the τₚ\u003csub\u003er\u003c/sub\u003eₑ, and the root mean square error (\u003cem\u003eRMSE\u003c/em\u003e), reflecting the average prediction error. Statistical significance was defined as α\u0026thinsp;=\u0026thinsp;0.05 (two-tailed). Descriptive data in text and table are reported as geometric mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation. Effect sizes were reported as partial eta squared (η\u0026sup2;ₚ) for repeated-measures ANOVA, Cohen\u0026rsquo;s \u003cem\u003ed\u003c/em\u003e\u003csub\u003ez\u003c/sub\u003e for paired-samples and pairwise comparisons, and \u003cem\u003er\u003c/em\u003e for Wilcoxon signed-rank test. All \u003cem\u003et\u003c/em\u003e tests, repeated-measures ANOVA, Bonferroni post hoc tests, effect size calculations, linear mixed-modeling, and Random Forest analyses were conducted using custom Python scripts (version 3.11.4), while Dunnett post hoc tests were performed in R (version 4.4.3).\u003c/p\u003e\u003c/div\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eALL\u003csub\u003ehams\u003c/sub\u003e, all hamstring motor points\u003c/p\u003e\u003cp\u003eALL\u003csub\u003equads\u003c/sub\u003e, all quadricep motor points\u003c/p\u003e\u003cp\u003eANOVA, analysis of variance\u003c/p\u003e\u003cp\u003eBF, biceps femoris\u003c/p\u003e\u003cp\u003eBF\u003csub\u003elh\u003c/sub\u003e, biceps femoris \u0026ndash; long head\u003c/p\u003e\u003cp\u003eBF\u003csub\u003esh\u003c/sub\u003e, biceps femoris \u0026ndash; short head\u003c/p\u003e\u003cp\u003eFES, functional electrical stimulation\u003c/p\u003e\u003cp\u003eiMPS, individual motor point stimulation\u003c/p\u003e\u003cp\u003eMPS, motor point stimulation\u003c/p\u003e\u003cp\u003emMPS, multiple motor point stimulation\u003c/p\u003e\u003cp\u003eMTSI, maximal tolerable stimulation intensity\u003c/p\u003e\u003cp\u003eMVC, maximal voluntary contraction\u003c/p\u003e\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e, coefficient of determination\u003c/p\u003e\u003cp\u003eRF, rectus femoris\u003c/p\u003e\u003cp\u003eRF\u003csub\u003ed\u003c/sub\u003e, rectus femoris \u0026ndash; distal\u003c/p\u003e\u003cp\u003eRF\u003csub\u003ep\u003c/sub\u003e, rectus femoris \u0026ndash; proximal\u003c/p\u003e\u003cp\u003eRMSE, root mean squared error\u003c/p\u003e\u003cp\u003eSES, single-electrode stimulation\u003c/p\u003e\u003cp\u003eSES\u003csub\u003ehams\u003c/sub\u003e, single-electrode stimulation \u0026ndash; hamstrings\u003c/p\u003e\u003cp\u003eSES\u003csub\u003equads\u003c/sub\u003e, single-electrode stimulation \u0026ndash; quadriceps\u003c/p\u003e\u003cp\u003eSM, semimembranosus\u003c/p\u003e\u003cp\u003eST, semitendinosus\u003c/p\u003e\u003cp\u003eTDI, torque deviation index\u003c/p\u003e\u003cp\u003eVL, vastus lateralis\u003c/p\u003e\u003cp\u003eVL\u003csub\u003ed\u003c/sub\u003e, vastus lateralis \u0026ndash; distal\u003c/p\u003e\u003cp\u003eVL\u003csub\u003ei\u003c/sub\u003e, vastus lateralis \u0026ndash; intermediate\u003c/p\u003e\u003cp\u003eVL\u003csub\u003ep\u003c/sub\u003e, vastus lateralis \u0026ndash; proximal\u003c/p\u003e\u003cp\u003eVM, vastus medialis\u003c/p\u003e\u003cp\u003eVM\u003csub\u003ed\u003c/sub\u003e, vastus medialis \u0026ndash; distal\u003c/p\u003e\u003cp\u003eVM\u003csub\u003ep\u003c/sub\u003e, vastus medialis \u0026ndash; proximal\u003c/p\u003e\u003cp\u003eη\u0026sup2;ₚ, partial eta squared\u003c/p\u003e\u003cp\u003eτ\u003csub\u003eobs\u003c/sub\u003e, observed torque\u003c/p\u003e\u003cp\u003eτ\u003csub\u003epre\u003c/sub\u003e, predicted torque\u003c/p\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003cp\u003eThe studies involving human participants were reviewed and approved by University Health Network (21-5946) Research Ethics Boards. The participants provided their written informed consent to participate in accordance with the Declaration of Helsinki.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003cp\u003e All authors read and approved the final manuscript for submission for publication.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis study was supported by the New Frontiers in Research Fund (grant no. NFRFE-2022-00620). Benjamin Kozlowski was supported by the Canadian Graduate Scholarship \u0026ndash; Masters from the Natural Sciences and Engineering Research Council of Canada.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eB.K., D.L., and K.M. conceptualized and designed the study. B.K. and M.G. collected the data and performed analyses. B.K., D.L., and K.M. curated, analyzed, and interpreted the data. B.K. and prepared the figures and table. B.K. and K.M. drafted the manuscript. K.M. and A.A. provided funding support and supervision. All authors reviewed and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors would like to thank all those who participated in the study. The authors would also like to thank Azim Rashidi for his technical support.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets generated and analyzed during the current study are available from the corresponding author, Kei Masani, upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003ePopovic MR, Masani K, Milosevic M. Functional Electrical stimulation therapy: mechanisms for recovery of function following spinal cord injury and stroke. In: Reinkensmeyer DJ, Marchal-Crespo L, Dietz V, editors. Neurorehabilitation Technology [Internet]. 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Effect of muscle length on maximum evoked torque, discomfort, contraction fatigue, and strength adaptations during electrical stimulation in adult populations: A systematic review. PLoS One. 2024;19(6):e0304205.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAlon G, V Smith G. Tolerance and conditioning to neuro-muscular electrical stimulation within and between sessions and gender. J Sports Sci Med. 2005;4(4):395\u0026ndash;405.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMaughan RJ, Watson JS, Weir J. Strength and cross-sectional area of human skeletal muscle. J Physiol. 1983;338:37\u0026ndash;49.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFarahmand F, Sejiavongse W, Amis AA. Quantitative study of the quadriceps muscles and trochlear groove geometry related to instability of the patellofemoral joint. Journal of Orthopaedic Research. 1998;16(1):136\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHori M, Suga T, Terada M, Miyake Y, Nagano A, Isaka T. Torque-producing capacity is affected by moment arm in the human knee extensors. BMC Res Notes. 2020 July 20;13(1):343.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOlewnik Ł, Ruzik K, Szewczyk B, Podg\u0026oacute;rski M, Aragon\u0026eacute;s P, Karauda P, et al. The relationship between additional heads of the quadriceps femoris, the vasti muscles, and the patellar ligament. Biomed Res Int. 2022;2022:9569101.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGrob K, Manestar M, Filgueira L, Ackland T, Gilbey H, Kuster MS. New insight in the architecture of the quadriceps tendon. J Exp Orthop. 2016;3(1):32.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"biomedical-engineering-online","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmeo","sideBox":"Learn more about [BioMedical Engineering OnLine](http://biomedical-engineering-online.biomedcentral.com/)","snPcode":"12938","submissionUrl":"https://submission.nature.com/new-submission/12938/3","title":"BioMedical Engineering OnLine","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"functional electrical stimulation, hamstrings, motor point, neuromuscular electrical stimulation, neurorehabilitation, orthotic, quadriceps, spinal cord injury, tetanic, torque","lastPublishedDoi":"10.21203/rs.3.rs-7782510/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7782510/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e\u003cp\u003eFunctional electrical stimulation (FES) delivers transcutaneous electrical current to motor nerves to artificially evoke muscle contractions and produce joint torque. In neurorehabilitation, FES is commonly applied via a large surface electrode pair placed over a muscle group \u0026ndash; an approach that we here refer to as single-electrode stimulation (SES). However, the torque-generating capacity of SES is limited. Targeting specific regions of high electrical excitability, or motor points, may enhance neuromuscular activation and increase joint torque output. Here we tested whether continuous multiple motor point stimulation (mMPS) increases tetanic knee torque compared with SES in the quadriceps and hamstrings. We also quantified quadriceps recruitment overlap as a secondary aim. We evaluated quadriceps and hamstring responses to mMPS and SES in neurologically intact participants, recording tetanic knee torque and assessing recruitment overlap relative to maximal voluntary contraction (MVC).\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eStimulating all quadriceps motor points produced approximately 51% greater knee extension torque than SES (33.3% MVC vs. 22.1% MVC). In contrast, stimulating all hamstring motor points did not significantly increase knee flexion torque. Within the quadriceps, proximal and intermediate vastus lateralis motor points contributed the most to knee extension torque, whereas the distal motor point had no significant effect. Discrepancies between observed and predicted MPS torques were primarily associated with rectus femoris stimulation, while vastus medialis contributed the least.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e\u003cp\u003eStimulation of all quadriceps motor points generated 51% greater knee extension torque compared with conventional SES, highlighting the potential of mMPS to improve the effectiveness of FES interventions. Optimization of motor point selection should emphasize proximal and intermediate vastus lateralis sites, while also including vastus medialis. Rectus femoris stimulation should be considered only when channel allocation permits and when the torque benefit outweighs redundancy. In contrast, hamstring stimulation did not yield additional knee flexion torque underscoring muscle-specific limitations. These findings provide practical guidance for electrode placement and channel allocation, suggesting that optimal quadriceps stimulation can be achieved by prioritizing a limited subset of motor points.\u003c/p\u003e","manuscriptTitle":"Multiple motor point stimulation increases tetanic knee torque versus conventional single- electrode functional electrical stimulation: implications for functional output and neurorehabilitation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-29 12:09:10","doi":"10.21203/rs.3.rs-7782510/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-11-20T15:19:53+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-18T09:42:32+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-04T22:32:18+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-29T16:36:37+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"1731664839188940731196859929535473565","date":"2025-10-15T18:27:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"68730723296519316447486523796201141406","date":"2025-10-15T15:58:00+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"294070749762881438086803421723070863436","date":"2025-10-14T23:07:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"294555757019146351455473907091729101040","date":"2025-10-14T21:37:07+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-14T20:19:57+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-10-09T14:50:26+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-10-08T09:09:36+00:00","index":"","fulltext":""},{"type":"submitted","content":"BioMedical Engineering OnLine","date":"2025-10-05T03:11:00+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"biomedical-engineering-online","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmeo","sideBox":"Learn more about [BioMedical Engineering OnLine](http://biomedical-engineering-online.biomedcentral.com/)","snPcode":"12938","submissionUrl":"https://submission.nature.com/new-submission/12938/3","title":"BioMedical Engineering OnLine","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"712cbccc-f620-4ef6-97a0-81e68550b0d0","owner":[],"postedDate":"October 29th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-28T20:09:29+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-29 12:09:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7782510","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7782510","identity":"rs-7782510","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}