Lower extremity electromyographic characteristics of patients with noncontact complete anterior cruciate ligament rupture not reconstructed in one-legged jump landings: a case-control study

Lower extremity electromyographic characteristics of patients with noncontact complete anterior cruciate ligament rupture not reconstructed in one-legged jump landings: a case-control study | 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 Article Lower extremity electromyographic characteristics of patients with noncontact complete anterior cruciate ligament rupture not reconstructed in one-legged jump landings: a case-control study Jie Xu, Meng Chen, Jing Ran, Xiaobing Luo This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6633756/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Nov, 2025 Read the published version in Scientific Reports → Version 1 posted 11 You are reading this latest preprint version Abstract There have been many studies on neuromuscular adaptation after anterior cruciate ligament (ACL) reconstruction, while the understanding of muscle activation patterns in unreconstructed patients with ACL rupture is still limited. The aim of this study was to investigate the lower limb electromyographic characteristics of unreconstructed patients with complete ACL rupture in a single-legged hopping landing task in order to deepen the understanding of motor control strategies in the ACL-deficient state and to provide a reference for rehabilitation assessment and intervention. Forty-two subjects were recruited for this study using a case-control design, with an ACL injury group (n = 21) of patients with unilateral non-contact complete rupture without reconstruction and a control group (n = 21) of healthy individuals matched for gender, dominant leg, and level of exercise. All subjects completed a single-leg hop landing task and synchronized Noraxon Ultium surface EMG signals with Bertec force plate data via the QUALISYS 3D motion capture system. EMG data were recorded from the lateral femoral (VL), medial femoral (VM), biceps femoris (BF), semitendinosus (ST), and gluteus maximus (Gmax) muscles before and after the landing for 100 ms each. Calculated metrics included activation onset time (onset-IC), peak appearance time (peak-IC), activation duration, and standardized root mean square (RMS) values. Data were analyzed by two-way ANOVA or nonparametric Scheirer-Ray-Hare test, and the significance level was set at P < 0.05. BF (P = 0.0409) and Gmax (P = 0.0469) sustained activation of the dominant leg in the injury group was significantly longer than that of the dominant leg in the control group. The onset-IC of BF (P = 0.0457), ST (P = 0.0277), and Gmax (P = 0.0192) of the dominant leg in the injury group was significantly earlier than that of the dominant leg in the control group. The peak-IC of BF (P = 0.0457) and ST (P = 0.0280) of the dominant leg in the injury group was significantly later than that of the dominant leg in the control group. The peak RMS of VL (P = 0.0171), VM (P = 0.0054), and Gmax (P = 0.0003) in the dominant leg of the injury group was significantly lower than that of the dominant leg of the control group in 100 ms after IC. Unreconstructed patients, averaging 18 months after ACL injury, continued to maintain a similar muscle pre-activation sequence as healthy individuals during the jump landing task, but showed a prolonged activation duration and reduced activation intensity, suggesting that neuromuscular activity was adjusted to maintain the kinematic profile. The delay in the peak of the posterior muscle groups (especially BF and ST) may be used to synergize tibial rearward movement and reduce forward movement and internal rotation, thus constituting a compensatory protective mechanism. The results of this study provide evidence for neuromuscular adaptation in the ACL-deficient state and are informative for preoperative functional assessment and rehabilitation intervention strategies. Health sciences/Health care/Disease prevention Health sciences/Health care/Therapeutics/Rehabilitation Health sciences/Risk factors ACL noncontact injury surface electromyography rehabilitation isometric muscle strength root mean square amplitude Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Anterior cruciate ligament (ACL) injury is one of the common knee injuries in clinical practice, which seriously affects the athletic ability and knee stability of patients. According to statistics, ACL rupture occurs in about 250,000 people per year in the United States 1 , the incidence rate in Sweden is about 78–81 cases/100,000 people/year 2 , and the rate of ACL injury in Chinese national-level athletes is about 0.47% 3 . The incidence of ACL injuries and reconstruction is on the rise as the percentage of youth participating in competitive sports increases, and as middle-aged and older adults remain physically active for longer periods of time. Although ACL reconstruction has become the mainstay of treatment for this injury, the risk of postoperative re-injury cannot be ignored. Studies have shown that the risk of ACL rupture on the healthy side after the first reconstruction is even higher than the risk of re-injury on the affected side 4,5 . In addition, $ 7.6 billion versus $ 17.7 billion is spent annually on ACL reconstruction and its rehabilitation in the United States, demonstrating the importance of this type of injury in the burden of disease 6 . Mechanistically, non-contact ACL ruptures account for approximately 72%-95% of all injuries 7 and occur in highly dynamic athletic situations such as jumping and landing, stopping sharply to change direction, etc. 8 . These injuries are usually not directly caused by external forces, but are closely related to the individual's inherent movement patterns, and are therefore considered to be preventable through intervention 9 . Of particular interest is the significantly higher rate of re-injury to the healthy side in patients with ACL injuries, but it is not clear whether this phenomenon is triggered by pre-existing functional imbalances or compensatory movement patterns due to functional adaptations in the affected limb 10 . Current surface electromyography studies of neuromuscular activity after ACL injury have focused on major motor groups such as the quadriceps, hamstrings, and calf triceps 11 , and relatively few studies have examined the role of the gluteus maximus muscle in the dynamic control of the knee joint. It has been shown that insufficient gluteal control can lead to dynamic valgus of the knee, thereby increasing the risk of non-contact ACL injury 12 . In addition, myoelectric analysis of relatively low-impact functional tasks such as walking 13 , running 14 , and squatting 15 have been used in the literature, mostly in individuals after ACL reconstruction, and the muscles of interest are mainly the quadriceps and hamstrings 16,17 , and there is a lack of research on the mechanisms of muscle activation in non-reconstructed patients during high-dynamic maneuvers. Based on the above deficiencies, this study was conducted in patients with chronic non-contact ACL complete rupture without reconstructive treatment, using a single-leg hopping landing task to analyze the activation of their affected limbs versus control individuals in the vastus lateralis (VL), vastus medialis (VM), and biceps femoris (BF), Semitendinosus (ST) and gluteus maximus (Gmax), key muscle groups, were characterized by activation timing, activation duration and activation intensity. We hypothesized that the neuromuscular system of patients with ACL rupture for more than six months has undergone adaptive reorganization, which is manifested by early activation, prolonged activation duration, or enhanced activation intensity of certain muscles, to compensate for the effects of ACL deficiency on knee stability and to achieve landing kinematic patterns similar to those of healthy individuals. 2. Materials and methods 2.1 Participant Recruitment The study used G*Power 3.1 software for sample size estimation. The level of significance was set at α = 0.05, and the target statistical power was 80%. Based on Cohen's recommendation 18 , the effect size (ES) was set at 0.46, and the minimum required sample size was calculated to be 40 individuals (20 in each group) using a two-way ANOVA model. Considering a dropout rate of approximately 10%, the final plan was to include 22 subjects in each group, for a total of 44, to ensure adequate statistical efficacy. All patients with ACL injuries completed testing before undergoing ACL reconstruction. Healthy individuals of the same sex, dominant leg side, and similar level of exercise (Tegner score not differing by more than ± 1 point) were screened by questionnaire to serve as the control group. All participants signed informed consent forms prior to the experiment. All methods were carried out in accordance with relevant guidelines and regulations, including the Good Clinical Practice (GCP) guidelines and the Declaration of Helsinki. The study protocol was approved by the Ethics Committee of Sichuan Orthopedic Hospital (Ethics No. KY2020-017-01). The inclusion criteria were: injury group: 1) age 18–35 years old; 2) mode of injury was non-contact injury; 3) the patient's injured leg was his/her dominant leg. We have determined that the patient's dominant leg did not change before or after the injury (the dominant leg is defined as the leg preferred for kicking, standing, jumping, or stepping on a box); 4) MRI showed a complete rupture of the ACL alone; 5) the duration of the disease was more than six months; 6) there was no injury to the adjacent joints; and 7) there was no underlying disease such as gout or rheumatoid arthritis. Control group: 1) Age: 18–35 years old, regardless of gender; 2) No motor system diseases in the last six months; 3) No history of lower limb surgery. 2.2 Data collection In this study, a QUALISYS 3D motion capture system (Model Oqus 300, Sweden) was synchronized with a Noraxon wireless surface EMG system (Model Ultium EMG, sampling frequency 2000 Hz, USA) and a Bertec force table (Model FP4060-08, sampling frequency 200 Hz, USA) for motion data acquisition. The force table was used to detect the initial contact (IC) time, defined as the instant when the vertical ground reaction force first exceeded 10N19. EMG acquisition sites were referenced to the SENIAM standardized localization guidelines 20 as detailed in Supplementary Table 1. Subjects underwent a 10-minute warm-up prior to testing, consisting of 5 minutes of jogging with 5 minutes of dynamic stretching. After warming up, the area to which the electrodes were attached was prepared by cleaning with 75% alcohol, shaving, exfoliating with fine sandpaper, and again cleaning with an alcohol cotton ball and air-drying to minimize skin surface impedance. Subsequently, silver/silver chloride electrodes (model CH3236, CATHAY, China) were affixed with an electrode spacing of 20 mm 21 , the reference electrode was kept equidistant from the acquisition electrode and secured against dislodgement by means of a muscle patch with medical adhesive tape (see Fig. 1 ) 22 . In my test procedure, the one-legged jump landing task was given first priority, followed by the maximal voluntary contraction (MVC) test, with a 5-minute rest period between the two. Subjects were asked to stand with their feet shoulder-width apart on a 30 cm raised platform, with the distance between the platform and the center of the force plate set at 80% of the distance from the subject's anterior superior iliac spine to the medial ankle 23 . The EMG signals were recorded before the start of the jump, and the subjects maintained a one-legged standing position on command, stabilized and jumped forward without initial velocity, and remained stationary for 3 seconds after landing on one foot. Each subject completed 5 tests at 1-minute intervals; no discomfort was experienced throughout the procedure (see Fig. 2 ). Maximum voluntary contraction (MVC) testing was performed using the David isometric device, which measures the maximum flexion and extension forces of the anterior and posterior thigh muscle groups, respectively. For the gluteus maximus MVC test, the subject was lying prone on a yoga mat with the legs abducted about 30°, the knees flexed 90°, and the hip joint in 0° extension. The experimenter applied resistance to the lower and middle thighs with his bare hands, and the subject tried his best to complete the hip extension and abduction movements under the oral command, with the knee joint slightly off the ground (about 2–3 cm) and holding it for 5 seconds 24 . All MVC tests were repeated 3 times at 30-second intervals with strong verbal encouragement to elicit maximal force output 25 . The MVC tests for the BF and ST muscles are shown in Fig. 3 . 2.3 Data processing a. VL, VM, BF, ST, Gmax muscle activation timing metrics The raw surface electromyography (SEMG) signals were first visually inspected to ensure that the acquired data were complete and valid. Subsequently, the DC offset was removed using Noraxon Ultium EMG software and a fourth-order zero-delay Butterworth high-pass filter (cutoff frequency fc = 15 Hz) was applied to remove motion artifacts. To extract temporal features of muscle activation, the filtered signal was full-wave rectified and a low-pass filter (fc = 20 Hz) was applied to generate a linear envelope signal. By experimenting with cutoff frequencies in the range of 10–25 Hz (in steps of 1 Hz), 20 Hz was finally selected as the low-pass filtering threshold, a parameter that maximizes the retention of key features consistent with changes in muscle tone 26 . The identification of muscle activation timing was based on a threshold of 15% of the maximum amplitude of the linear envelope signal: when 28 consecutive sampling points (sampling frequency 2000 Hz) exceeded or fell below this threshold, respectively, they were considered as the beginning and the end of muscle activation 27 . After several rounds of comparison and manual calibration in the range of 3%-25% thresholds, 15% was finally determined as the optimal threshold. All automatically extracted time points were visually verified manually to ensure that the analysis results accurately reflected the real muscle activation characteristics 28 . The final extracted temporal metrics included: the duration of muscle activation (ms); the time difference of activation onset time relative to initial contact (IC) (onset-IC, ms); and the time difference of peak EMG appearance time relative to IC (peak-IC, ms). b. VL, VM, BF, ST, Gmax muscle activation strength indicators Raw SEMG signals were full-wave rectified, smoothed using a moving-window (50 ms) root mean square (RMS) algorithm, and normalized by the peak value recorded during MVC. Muscle activation intensity indices were divided into the following two categories: preparatory muscle activity: peak and mean RMS values within a 100 ms window before IC; reactive muscle activity: peak and mean RMS values within a 100 ms window after IC. 2.4 Statistical analysis Raw data were entered and organized using Microsoft Excel, and statistical analysis was done using GraphPad Prism 9.5 software. All continuous variables were first assessed for normality by the Shapiro-Wilk test, and Levene's test for chi-square was used. For variables that satisfied both normal distribution and chi-square, a two-way ANOVA was used, with "group" (ACL injury group vs. control group) as a between-group factor and "limb side" (dominant vs. nondominant leg) as a within-group factor. If main effects or interactions were significant, post hoc two-by-two comparisons were further performed using Fisher's LSD method. Scheirer-Ray-Hare nonparametric tests were used for variables that did not meet the assumption of normality. All data are presented as mean ± standard deviation and the significance level was set at P < 0.05. 3 Results 3.1 Baseline characteristics of participants During the testing process, one subject in the injury group withdrew from the trial because she gave up ACL reconstruction surgery and chose conservative treatment; one subject in the control group was excluded because she was unable to complete all the tests due to scheduling conflicts. In the end, a total of 42 subjects completed all the tests, including 21 in the injury group and 21 in the control group. Among them, 22 were male and 20 were female. The basic information of the subjects is shown in Table 1 . Table 1 Basic information of subjects Injury group (N = 21) Control group (N = 21) t-value p-value Gender (M/F) 11/10 11/10 Age (y) 26.97 ± 4.35 24.66 ± 3.65 1.861 0.0702 Height (cm) 170.80 ± 10.92 172.40 ± 4.85 0.6298 0.5324 Weight (kg) 68.03 ± 12.25 72.47 ± 8.43 1.366 0.1794 BMI (kg/m2) 22.67 ± 2.94 23.92 ± 2.65 1.449 0.1552 Tegner Rating 5.14 ± 1.35 5.29 ± 1.3 0.3478 0.7298 Duration of injury (months) 18.20 ± 7.23 3.2 Muscle activation duration Since no significant interaction effect was presented between subject group and test limb, the main effects of the group factor and limb factor were analyzed separately, and the results are shown in Table 2 . In terms of muscle activation duration, subject group showed a significant main effect on BF (F (1,40) = 4.732; P = 0.0326), with the duration of activation of the dominant leg in the injury group being significantly longer than that of the dominant leg in the control group (P = 0.0409). A significant main effect was also shown for Gmax (F (1,40) = 5.961; P = 0.0168), which likewise showed a significantly longer duration of sustained activation of the dominant leg in the injury group (P = 0.0469). Table 2 Duration of sustained activation of each muscle comparison (ms) Muscle Injury group Control group p-valuea Dominant leg (Affected limb) Non-dominant leg (Healthy limbs) Dominant leg Non-dominant leg VL 354.12 ± 101.82 339.37 ± 84.57 337.64 ± 87.35 329.28 ± 105.18 0.8781 VM 336.45 ± 77.18 322.16 ± 80.08 311.22 ± 82.60 321.59 ± 86.27 0.4906 BF 346.61 ± 73.52 335.16 ± 65.84 305.52 ± 55.67* 315.43 ± 59.81 0.4472 ST 347.34 ± 66.86 338.24 ± 65.05 311.34 ± 57.10 319.97 ± 54.78 0.5084 Gmax 261.39 ± 52.60 257.49 ± 49.75 230.04 ± 42.81* 235.21 ± 55.30 0.6808 Note: a , indicates the effect of subject group× test limb interactions on the muscle sustained activation time;*, indicates p < 0.05 for comparison (a), indicates the effect of subject group test limb interactions on the muscle sustained activation time;*, indicates p < 0.05 for comparison between the dominant leg in the injury group and the other groups. 3. 3 Synchronization of myoelectric activity across muscles Since there was no significant interaction effect between subject group and test limb, the main effects of the two factors were analyzed separately in this section, and the results are shown in Table 3 and Fig. 4 . In the comparison of onset-IC, the subject group showed a significant main effect on BF (F (1,40) = 5.127; P = 0.0351), with onset-IC for the dominant leg in the injury group significantly earlier than that for the control group's dominant leg (P = 0.0457).ST also showed a significant main effect (F (1,40) = 6.314; P = 0.0239), with the onset-IC of the dominant leg in the injury group being significantly earlier than that of the dominant leg in the control group (P = 0.0277) and that of its own non-dominant leg (P = 0.0405). In addition, Gmax also showed a significant main effect (F (1,40) = 4.053; P = 0.0474), as evidenced by a significantly earlier onset-IC in the dominant leg of the injury group than in the dominant leg of the control group (P = 0.0192). In the comparison of peak-IC, BF showed a significant main effect (F (1,40) = 4.040; P = 0.0415), in which the peak-IC of the dominant leg in the injury group was significantly later than that of the dominant leg in the control group (P = 0.0457).ST also showed a significant main effect (F (1,40) = 7.271; P = 0.0190), with the dominant leg in the injury group having the peak-IC significantly later than the control dominant leg (P = 0.0280). Table 3 Comparison of onset-IC and peak-IC by muscle (ms) Muscle Injury group Control group p-valuea Dominant leg (Affected limb) Non-dominant leg (Healthy limbs) Dominant leg Non-dominant leg onset-IC VL -125.37b ± 45.43 -118.35 ± 42.95 -109.62 ± 43.79 -114.26 ± 41.25 0.5398 VM -120.84 ± 37.17 -114.66 ± 35.49 -109.57 ± 30.27 -103.36 ± 34.34 0.9985 BF -150.55 ± 66.04 -136.83 ± 63.47 -112.86 ± 55.67* -129.28 ± 54.67 0.2544 ST -156.59 ± 66.93 -117.49 ± 59.10* -114.49 ± 60.71* -120.41 ± 56.07 0.0938 Gmax -95.61 ± 20.02 -87.79 ± 17.67 -82.16 ± 18.36* -85.21 ± 16.77 0.1760 peak-IC VL 151.26 ± 46.87 161.37 ± 48.72 148.41 ± 52.06 133.63 ± 57.14 0.2701 VM 146.64 ± 59.81 148.22 ± 65.44 157.80 ± 74.42 160.71 ± 70.32 0.9643 BF -34.21 ± 12.22 -40.31 ± 16.74 -42.83 ± 10.38* -37.25 ± 13.11 0.0578 ST -32.15 ± 12.46 -38.14 ± 13.78 -40.36 ± 11.33* -38.34 ± 9.59 0.1267 Gmax 41.47 ± 12.04 39.26 ± 12.44 40.08 ± 10.37 37.82 ± 12.20 0.9924 Note: a , indicates the effect of subject group× test limb interactions on the onset-IC and peak-IC time of muscle; b , negative values indicate that they occurred before initial contact (IC); *, indicates p < 0.05 for comparison of the dominant leg in the injury group versus the other groups. 3. 4 Characterization of EMG activation intensity by muscle For the RMS peak versus mean within 100 ms before and after IC, there was no significant interaction effect between subject group and test limb, so the main effect of subject group versus test limb was analyzed, as shown in Figs. 5 and 6 . Specific P values for the multiple comparisons results are detailed in Supplementary Table 2. There was a significant main effect of subject group on the peak RMS of the VL within 100 ms after IC (F (1,40) = 4.742; P = 0.0324), and the dominant leg in the injury group was significantly lower than the dominant leg in the control group (P = 0.0171). There was a significant main effect of subject group on the peak RMS of VM within 100 ms after IC (F (1,40) = 6.007; P = 0.0164), with the dominant leg in the injury group being significantly lower than the dominant leg in the control group (P = 0.0054) and the non-dominant leg in the control group (P = 0.0253). There was a significant main effect of subject group on the mean RMS of VM within 100 ms after IC (F (1,40) = 6.925; P = 0.0102), which was significantly lower for the dominant leg in the injury group (P = 0.0178) and the nondominant leg in the injury group (P = 0.0357) than for the dominant leg in the control group. There was a significant main effect of subject group on the peak RMS of ST within the first 100 ms of IC (F (1,40) = 6.429; P = 0.0132), which was significantly higher in the dominant leg of the injury group than in the dominant leg of the control group (P = 0.0439) and the non-dominant leg of the control group (P = 0.0229). There was a significant main effect of subject group on the mean RMS of ST within the first 100 ms of IC (F (1,40) = 5.563; P = 0.0208), and the dominant leg was significantly higher in the injury group than the dominant leg in the control group (P = 0.0483). There was a significant main effect of subject group on the peak RMS of Gmax within 100 ms after IC (F (1,40) = 13.94; P = 0.0004), with the dominant leg in the injury group being significantly lower than the dominant leg in the control group (P = 0.0003) and the nondominant leg in the control group (P = 0.0122), and the nondominant leg in the injury group being significantly lower than the dominant leg in the control group (P = 0.0081). 4. Discussion ACL disruption is thought to disrupt pre-existing neuromuscular control strategies in the lower extremity. It has been shown that ACL injury can cause significant alterations in the kinematic, kinetic, and electromyographic characteristics of the lower extremity during high-impact tasks such as jump landings, and that these changes reflect a phenomenon of neuromuscular adaptation or reprogramming in response to joint instability aimed at enhancing the dynamic stability of the knee and reducing the risk of re-injury by modulating the order of activation, duration, and peak response. In the present study, we found that muscle activation durations were generally prolonged in the dominant leg of the ACL-injured group during a single-leg jump landing task, with BF and Gmax being the most significant. This result is consistent with previous findings regarding prolonged EMG durations in walking, such that the VM, VL, semitendinosus, and lateral popliteus showed similar trends 29,30 . The prolonged activation duration may represent a compensatory strategy for knee instability, increasing joint compressive forces by maintaining longer muscle contractions, thereby enhancing mechanical stability and compensating for limitations caused by ACL deficits, resulting in a kinematic profile similar to that of the healthy side. In terms of muscle activation timing, the present study observed that the onset of activation (onset-IC) of several key muscle groups in the ACL-injured group was significantly earlier than that of the control group, especially the posterior masseter muscles (BF, ST) and Gmax. This early pre-activation pattern was considered as part of the "pretension conditioning" during landing, which aims to By preactivating the muscles a sufficiently stable base prior to contact with the ground to control knee trajectory and absorb ground reaction forces. In the case of the quadriceps muscle, for example, it has been shown that healthy individuals preactivate the VM and VL 103–114 ms before ground contact, and the injury group in this study showed a similar or even earlier activation sequence. In addition, there is an electromechanical delay (EMD) between the EMG signal and actual tension generation, which ranges from 20–100 ms for knee extensors 31 and may reach 55–92 ms for hamstrings 32 , making early activation particularly critical. Analysis of the time of peak EMG appearance (peak-IC) revealed that both BF and ST peaks were significantly delayed in the ACL injury group, which is highly consistent with the popliteal mechanism of action. The hamstrings are the main co-stabilizing muscles of the ACL by generating tibial "posterior drawer force" to resist anterior displacement. During landing maneuvers, peak tibiofemoral shear occurs approximately 28–30 ms after touchdown 26,27 . Therefore, a delay in maximal hamstring output to this stage coincides with the most vulnerable window of the ACL, thus forming a dynamic protective barrier. Blackburn et al. 32 state that hamstring EMD is 72 ms, which is highly consistent with the result that hamstrings reach peak activity approximately 30–40 ms before touchdown. This is highly consistent with the result that the hamstrings reach peak activity around 30–40 ms before touchdown. Further, Gmax showed a similar pattern of regulation. Not only was Gmax activated earlier before touchdown in the ACL injury group, its peak activation also occurred around 40 ms after landing, and the abduction moment generated by Gmax was expected to peak 92 ms after landing. This coincides with the electromechanical delay (52 ms on average) in hip abduction proposed by Kim et al. 33 , suggesting that its abduction output is functioning right at the peak tibiofemoral shear force phase. It has been reported that the peak knee valgus angle mostly occurs 85 ms after landing (range 70–100 ms), and more than 60% of athletes reach their maximal knee valgus angle at this stage 34,35 . Therefore, early activation of Gmax helps to counteract the tendency of hip adduction and knee valgus and prevents pelvic instability from adversely affecting the knee joint. Overall, patients with ACL injuries show a typical "pre-activation-post-peak" bi-directional strategy in landing tasks: key muscle groups are activated early to pre-establish muscle tone in response to ground impact, and the peak is moderately delayed to match the timing of the peak of the ground reaction force and the emergence of shear forces, thus maximizing their ability to respond to ground impact. This adaptation pattern not only reflects the reorganization of the neuromuscular control system in the context of injury, but also provides an important biomechanical basis for preoperative patient rehabilitation assessment and intervention design. In the ACL-injured group, the peak EMG values of the quadriceps muscles (VL, VM) were significantly lower than those of the healthy control group within 100 ms after landing, suggesting that the activation of the knee extensor muscles during the touchdown phase was reduced. This feature is referred to as the "quadriceps avoidance strategy", reflecting the fact that patients may actively reduce extensor output to avoid knee instability, which affects joint braking and postural control 36 . In contrast, the hamstrings showed a tendency to increase activation, especially ST, which peaked significantly within 100 ms before touchdown, and BF, which tended to increase both before and after touchdown. As a co-stabilizing muscle of the ACL, popliteus mainly limits anterior translation and internal rotation by generating tibial posterior moment, and its enhanced recruitment contributes to knee stability and compensates for the lack of ACL function. This feature fits with the electromechanical delay time of the hamstrings, which ensures the provision of an effective response during the peak phase of shear 30 . Gmax, although showing a reduced peak after landing in the injury group, has an earlier onset and longer duration, suggesting that it compensates through temporal regulation to maintain hip and pelvic stability. Hamstrings take on more loads when the function of Gmax is reduced, and their enhanced activation may also partly stem from the indirect compensation for gluteal insufficiency 37 . In addition, ACL injury may interfere with central drive, resulting in decreased efficiency of motor unit recruitment, further exacerbating Gmax underactivation 38 . Overall, the ACL-injured group showed an activation pattern of "extensor inhibition - flexor strengthening - gluteal sequential compensation", which reflects the self-regulation mechanism of the neuromuscular system under the condition of impaired joint stability. The results suggest that hamstring and gluteal muscle training should be emphasized in preoperative rehabilitation to optimize the stability of the kinetic chain and reduce the risk of landing-related injuries. The relatively limited sample size of this study, which included only 21 patients with ACL injury and 21 healthy controls, and the age concentration of subjects in younger age groups may limit the generalizability of the findings. Future studies may expand the sample size and introduce subjects of different age groups to enhance the representativeness and external validity of the findings. In addition, the affected limbs of all patients with ACL injuries in this study were dominant legs, failing to explore the potential effects of limb dominance on EMG activation patterns. Therefore, follow-up studies are recommended to include a comparison of dominant versus nondominant legs in their design to further clarify the mechanism of limb laterality in neuromuscular control. 5. Conclusion In a single-leg jump landing task, patients with ACL injuries of an average disease duration of 18 months generally had a prolonged muscle activation duration, reflecting compensatory mechanisms to maintain kinematic stability, despite a preactivation sequence consistent with that of healthy individuals. Preactivation of the biceps femoris, semitendinosus, and gluteus maximus muscles in the affected limb occurred with delayed hamstring peaks, possibly enhancing knee stability by enhancing posterior tibial shift control and resisting excessive anterior translation and internal rotation. Declarations Conflict of interest: The authors do not have any potential conflicts of interest. Funding: No funding. Author Contribution J.X. and M.C. designed the research. J.X. and J.R. collected, analyzed the data, and drafted the manuscript. J.X. and XB. L. revised the manuscript. All authors contributed to the article and approved the submitted version. Acknowledgement The authors express gratitude to all participants. Data Availability The data supporting the findings of this study are available from the corresponding author upon reasonable request References Griffin, L. Y. et al. Understanding and preventing noncontact anterior cruciate ligament injuries: a review of the Hunt Valley II meeting, January 2005. AM J SPORT MED 34 1512 (2006). Nordenvall, R. et al. A population-based nationwide study of cruciate ligament injury in Sweden, 2001–2009: incidence, treatment, and sex differences. AM J SPORT MED 40 1808 (2012). Ao, Y., Yu, C. & Tian, D. Anterior Cruciate Ligament Injury in Female Athlete. Chinese Journal of Sports Medicine 19 387 (2000). Wright, R. W., Magnussen, R. A., Dunn, W. R. & Spindler, K. P. Ipsilateral graft and contralateral ACL rupture at five years or more following ACL reconstruction: a systematic review. J. BONE JOINT SURG. AM. 93 , 1159 (2011). Grassi, A. et al. More Than a 2-Fold Risk of Contralateral Anterior Cruciate Ligament Injuries Compared With Ipsilateral Graft Failure 10 Years After Primary Reconstruction. AM J SPORT MED 48 310 (2020). Baker, L. A. et al. Multivariate genome-wide association analysis identifies novel and relevant variants associated with anterior cruciate ligament rupture risk in the dog model. BMC GENET 19 39 (2018). Myklebust, G. et al. Prevention of anterior cruciate ligament injuries in female team handball players: a prospective intervention study over three seasons. CLIN J SPORT MED 13 71 (2003). Olsen, O. E., Myklebust, G., Engebretsen, L., Holme, I. & Bahr, R. Exercises to prevent lower limb injuries in youth sports: cluster randomised controlled trial. BMJ-BRIT MED J 330 449 (2005). Marshall, S. W. Recommendations for defining and classifying anterior cruciate ligament injuries in epidemiologic studies. J ATHL TRAINING 45 516 (2010). Paterno, M. V., Rauh, M. J., Schmitt, L. C., Ford, K. R. & Hewett, T. E. Incidence of contralateral and ipsilateral anterior cruciate ligament (ACL) injury after primary ACL reconstruction and return to sport. CLIN J SPORT MED 22 116 (2012). Theisen, D., Rada, I., Brau, A., Gette, P. & Seil, R. Muscle Activity Onset Prior to Landing in Patients after Anterior Cruciate Ligament Injury: A Systematic Review and Meta-Analysis. PLOS ONE 11 e155277 (2016). Rinaldi, V. G., Prill, R., Jahnke, S., Zaffagnini, S. & Becker, R. The influence of gluteal muscle strength deficits on dynamic knee valgus: a scoping review. J EXP ORTHOP 9 81 (2022). Ito, N., Capin, J. J., Khandha, A., Buchanan, T. S. & Snyder-Mackler, L. Identifying Gait Pathology after ACL Reconstruction Using Temporal Characteristics of Kinetics and Electromyography. MED SCI SPORT EXER 54 923 (2022). Georgoulis, J. D. et al. Neuromuscular activity of the lower-extremities during running, landing and changing-of-direction movements in individuals with anterior cruciate ligament reconstruction: a review of electromyographic studies. J EXP ORTHOP 10 43 (2023). Trulsson, A., Miller, M., Gummesson, C. & Garwicz, M. Associations between altered movement patterns during single-leg squat and muscle activity at weight-transfer initiation in individuals with anterior cruciate ligament injury. BMJ OPEN SPORT EXERC 2 e131 (2016). Zebis, M. K. et al. Effects of evidence-based prevention training on neuromuscular and biomechanical risk factors for ACL injury in adolescent female athletes: a randomised controlled trial. BRIT J SPORT MED 50 552 (2016). Wu, X. et al. Surface Electromyography and Gait Features in Patients after Anterior Cruciate Ligament Reconstruction. ORTHOP SURG (2024). Cohen, J. Statistical power analysis for the behavioral sciences (2nd ed. Statistical power analysis for the behavioral sciences, (1988). Swanik, C. B., Lephart, S. M., Giraldo, J. L., Demont, R. G. & Fu, F. H. Reactive muscle firing of anterior cruciate ligament-injured females during functional activities. J. ATHL Train. 34 , 121 (1999). Stegeman, D. & Hermens, H. Standards for surface electromyography: The European project Surface EMG for non-invasive assessment of muscles (SENIAM). Enschede: Roessingh Research and Development 10 8 (2007). Daanen, H. A., Mazure, M., Holewijn, M. & Van der Velde, E. A. Reproducibility of the mean power frequency of the surface electromyogram. Eur J Appl Physiol Occup Physiol 61 274 (1990). DeLuca, P. A., Davis, R. R., Ounpuu, S., Rose, S. & Sirkin, R. Alterations in surgical decision making in patients with cerebral palsy based on three-dimensional gait analysis. J. PEDIATR. ORTHOPED . 17 , 608 (1997). Nedergaard, N. J., Dalbø, S., Petersen, S. V., Zebis, M. K. & Bencke, J. Biomechanical and neuromuscular comparison of single- and multi-planar jump tests and a side-cutting maneuver: Implications for ACL injury risk assessment. KNEE 27 , 324 (2020). McCurdy, K., Walker, J. & Yuen, D. Gluteus Maximus and Hamstring Activation During Selected Weight-Bearing Resistance Exercises. J STRENGTH COND RES 32 594 (2018). Kang, S. Y., Jeon, H. S., Kwon, O., Cynn, H. S. & Choi, B. Activation of the gluteus maximus and hamstring muscles during prone hip extension with knee flexion in three hip abduction positions. Man Ther 18 303 (2013). Steele, J. R. & Brown, J. M. Effects of chronic anterior cruciate ligament deficiency on muscle activation patterns during an abrupt deceleration task. CLIN BIOMECH 14 247 (1999). Cowling, E. J. & Steele, J. R. Is lower limb muscle synchrony during landing affected by gender? Implications for variations in ACL injury rates. J ELECTROMYOGR KINES 11 263 (2001). Bryant, A. L., Newton, R. U. & Steele, J. Successful feed-forward strategies following ACL injury and reconstruction. J ELECTROMYOGR KINES 19 988 (2009). Lass, P. et al. Muscle coordination following rupture of the anterior cruciate ligament. Electromyographic studies of 14 patients. Acta Orthop Scand 62 9 (1991). Knoll, Z., Kiss, R. M. & Kocsis, L. Gait adaptation in ACL deficient patients before and after anterior cruciate ligament reconstruction surgery. J ELECTROMYOGR KINES 14 287 (2004). Zhou, S., Lawson, D. L., Morrison, W. E. & Fairweather, I. Electromechanical delay of knee extensors: the normal range and the effects of age and gender. OAI (1995). Blackburn, J. T., Bell, D. R., Norcross, M. F., Hudson, J. D. & Engstrom, L. A. Comparison of hamstring neuromechanical properties between healthy males and females and the influence of musculotendinous stiffness. J ELECTROMYOGR KINES 19 e362 (2009). Kim, J. W. et al. Age-sex differences in the hip abductor muscle properties. GERIATR GERONTOL INT 11 333 (2011). Koga, H., Nakamae, A., Shima, Y., Bahr, R. & Krosshaug, T. Hip and Ankle Kinematics in Noncontact Anterior Cruciate Ligament Injury Situations: Video Analysis Using Model-Based Image Matching. AM J SPORT MED 46 333 (2018). Krosshaug, T., Slauterbeck, J. R., Engebretsen, L. & Bahr, R. Biomechanical analysis of anterior cruciate ligament injury mechanisms: three-dimensional motion reconstruction from video sequences. SCAND J MED SCI SPOR 17 508 (2007). Wexler, G., Hurwitz, D. E., Bush-Joseph, C. A., Andriacchi, T. P. & Bach, B. J. Functional gait adaptations in patients with anterior cruciate ligament deficiency over time. CLIN ORTHOP RELAT R 166 (1998). Matsunaga, N. et al. Muscle fatigue in the gluteus maximus changes muscle synergies during single-leg landing. J BODYW MOV THER 27 493 (2021). Trulsson, A., Miller, M., Hansson, G., Gummesson, C. & Garwicz, M. Altered movement patterns and muscular activity during single and double leg squats in individuals with anterior cruciate ligament injury. BMC MUSCULOSKEL DIS 16 28 (2015). Additional Declarations No competing interests reported. Supplementary Files Supplementarytable.docx Cite Share Download PDF Status: Published Journal Publication published 28 Nov, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 17 Sep, 2025 Reviews received at journal 13 Sep, 2025 Reviewers agreed at journal 17 Aug, 2025 Reviewers agreed at journal 16 Aug, 2025 Reviewers agreed at journal 15 Jul, 2025 Reviews received at journal 25 Jun, 2025 Reviewers agreed at journal 05 Jun, 2025 Reviewers invited by journal 02 Jun, 2025 Editor assigned by journal 02 Jun, 2025 Submission checks completed at journal 20 May, 2025 First submitted to journal 20 May, 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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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6633756","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":466010645,"identity":"3d4dc162-62ee-41c0-a4f4-70b7cca94081","order_by":0,"name":"Jie Xu","email":"","orcid":"","institution":"Sichuan Provincial Orthopedics Hospital","correspondingAuthor":false,"prefix":"","firstName":"Jie","middleName":"","lastName":"Xu","suffix":""},{"id":466010646,"identity":"b67e84d5-f9b4-49e1-96ee-619b33fefa98","order_by":1,"name":"Meng Chen","email":"","orcid":"","institution":"Nanchong Hospital of Traditional Chinese Medicine","correspondingAuthor":false,"prefix":"","firstName":"Meng","middleName":"","lastName":"Chen","suffix":""},{"id":466010647,"identity":"1d2f4f30-fbd3-499d-bb70-9cf3337ae772","order_by":2,"name":"Jing Ran","email":"","orcid":"","institution":"Sichuan Provincial Orthopedics Hospital","correspondingAuthor":false,"prefix":"","firstName":"Jing","middleName":"","lastName":"Ran","suffix":""},{"id":466010648,"identity":"745bc615-d893-4ae2-afa2-c96e1c470cce","order_by":3,"name":"Xiaobing Luo","email":"data:image/png;base64,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","orcid":"","institution":"Sichuan Provincial Orthopedics Hospital","correspondingAuthor":true,"prefix":"","firstName":"Xiaobing","middleName":"","lastName":"Luo","suffix":""}],"badges":[],"createdAt":"2025-05-10 09:08:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6633756/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6633756/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-29516-y","type":"published","date":"2025-11-28T15:58:36+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":84201611,"identity":"22ac9267-3b2c-4854-a39f-8ba81da6deb9","added_by":"auto","created_at":"2025-06-09 08:32:25","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":19774,"visible":true,"origin":"","legend":"\u003cp\u003eVL, VM surface EMG acquisition site\u003c/p\u003e","description":"","filename":"image1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6633756/v1/abd6fabe6964ec69523c0c2c.jpeg"},{"id":84201615,"identity":"24712c3c-e7be-4c8e-9c14-c217dab8b1b3","added_by":"auto","created_at":"2025-06-09 08:32:25","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":31308,"visible":true,"origin":"","legend":"\u003cp\u003eOne-legged jump landing test\u003c/p\u003e","description":"","filename":"image2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6633756/v1/7b916dc3e2930c90617ea366.jpeg"},{"id":84201620,"identity":"e25a1299-1a96-47b9-934b-36efd25fac8c","added_by":"auto","created_at":"2025-06-09 08:32:25","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":180110,"visible":true,"origin":"","legend":"\u003cp\u003eMVC test diagram for VL and VM\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-6633756/v1/0b5f0a023b3ad88be3dee159.png"},{"id":84202907,"identity":"595f5696-8d88-4944-a8a3-7fc6c61e4f93","added_by":"auto","created_at":"2025-06-09 08:40:25","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":85687,"visible":true,"origin":"","legend":"\u003cp\u003ePre-activation sequence of each muscle before touchdown\u003c/p\u003e","description":"","filename":"image4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6633756/v1/abaae17ad0b4474e933501ba.jpeg"},{"id":84201622,"identity":"c8e5b11b-e060-402b-803e-e90740076f5e","added_by":"auto","created_at":"2025-06-09 08:32:25","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":88156,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of RMS in each muscle during the first 100 ms of IC\u003c/p\u003e\n\u003cp\u003eNote: DL indicates dominant leg; NDL, nondominant leg; *, indicates p\u0026lt;0.05 for comparison between the dominant leg in the injury group and the other groups; RMS, root-mean-square amplitude\u003c/p\u003e","description":"","filename":"image5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6633756/v1/f5e185bfdd94c65c49b3c1fd.jpeg"},{"id":84201619,"identity":"2d9bc112-7627-47e3-957a-d08564ab31d7","added_by":"auto","created_at":"2025-06-09 08:32:25","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":89207,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of RMS of each muscle within 100ms after IC\u003c/p\u003e\n\u003cp\u003eNote: DL indicates dominant leg; NDL indicates nondominant leg; *, indicates p\u0026lt;0.05 for comparison between the dominant leg and other groups in the injury group; **, indicates p\u0026lt;0.01 for comparison between the dominant leg and other groups in the injury group; ***, indicates p\u0026lt;0.001 for comparison between the dominant leg and other groups in the injury group; \u003csup\u003e#\u003c/sup\u003e, indicates p\u0026lt;0.05 for comparison between the nondominant leg and other groups in the injury group; (##), indicates p\u0026lt;0.01 for comparison between the nondominant leg and other groups in the injury group; RMS, indicates root mean square amplitude\u003csup\u003e.\u003c/sup\u003e\u0026lt;0.05; \u003csup\u003e##\u003c/sup\u003e, indicates p\u0026lt;0.01 between the non-dominant leg in the injury group and the other groups; RMS, indicates root mean square amplitude\u003c/p\u003e","description":"","filename":"image6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6633756/v1/eb5d419809ec86d84c954ce3.jpeg"},{"id":97179738,"identity":"5b9d6553-a469-4fcb-8032-9cc8b245a915","added_by":"auto","created_at":"2025-12-01 16:16:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1408524,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6633756/v1/05f5da43-1b92-431c-b13f-c6de17452232.pdf"},{"id":84201616,"identity":"72371cb0-5c76-4fff-ada6-38d94fbb4811","added_by":"auto","created_at":"2025-06-09 08:32:25","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":50212,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarytable.docx","url":"https://assets-eu.researchsquare.com/files/rs-6633756/v1/a9e1073aa55df94a7c475c63.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Lower extremity electromyographic characteristics of patients with noncontact complete anterior cruciate ligament rupture not reconstructed in one-legged jump landings: a case-control study","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAnterior cruciate ligament (ACL) injury is one of the common knee injuries in clinical practice, which seriously affects the athletic ability and knee stability of patients. According to statistics, ACL rupture occurs in about 250,000 people per year in the United States\u003csup\u003e1\u003c/sup\u003e, the incidence rate in Sweden is about 78\u0026ndash;81 cases/100,000 people/year\u003csup\u003e2\u003c/sup\u003e, and the rate of ACL injury in Chinese national-level athletes is about 0.47%\u003csup\u003e3\u003c/sup\u003e. The incidence of ACL injuries and reconstruction is on the rise as the percentage of youth participating in competitive sports increases, and as middle-aged and older adults remain physically active for longer periods of time. Although ACL reconstruction has become the mainstay of treatment for this injury, the risk of postoperative re-injury cannot be ignored. Studies have shown that the risk of ACL rupture on the healthy side after the first reconstruction is even higher than the risk of re-injury on the affected side\u003csup\u003e4,5\u003c/sup\u003e. In addition, \u003cspan\u003e$\u003c/span\u003e7.6\u0026nbsp;billion versus \u003cspan\u003e$\u003c/span\u003e17.7\u0026nbsp;billion is spent annually on ACL reconstruction and its rehabilitation in the United States, demonstrating the importance of this type of injury in the burden of disease\u003csup\u003e6\u003c/sup\u003e. Mechanistically, non-contact ACL ruptures account for approximately 72%-95% of all injuries\u003csup\u003e7\u003c/sup\u003e and occur in highly dynamic athletic situations such as jumping and landing, stopping sharply to change direction, etc.\u003csup\u003e8\u003c/sup\u003e. These injuries are usually not directly caused by external forces, but are closely related to the individual's inherent movement patterns, and are therefore considered to be preventable through intervention\u003csup\u003e9\u003c/sup\u003e. Of particular interest is the significantly higher rate of re-injury to the healthy side in patients with ACL injuries, but it is not clear whether this phenomenon is triggered by pre-existing functional imbalances or compensatory movement patterns due to functional adaptations in the affected limb\u003csup\u003e10\u003c/sup\u003e. Current surface electromyography studies of neuromuscular activity after ACL injury have focused on major motor groups such as the quadriceps, hamstrings, and calf triceps\u003csup\u003e11\u003c/sup\u003e, and relatively few studies have examined the role of the gluteus maximus muscle in the dynamic control of the knee joint. It has been shown that insufficient gluteal control can lead to dynamic valgus of the knee, thereby increasing the risk of non-contact ACL injury\u003csup\u003e12\u003c/sup\u003e. In addition, myoelectric analysis of relatively low-impact functional tasks such as walking\u003csup\u003e13\u003c/sup\u003e, running\u003csup\u003e14\u003c/sup\u003e, and squatting\u003csup\u003e15\u003c/sup\u003e have been used in the literature, mostly in individuals after ACL reconstruction, and the muscles of interest are mainly the quadriceps and hamstrings\u003csup\u003e16,17\u003c/sup\u003e, and there is a lack of research on the mechanisms of muscle activation in non-reconstructed patients during high-dynamic maneuvers.\u003c/p\u003e \u003cp\u003eBased on the above deficiencies, this study was conducted in patients with chronic non-contact ACL complete rupture without reconstructive treatment, using a single-leg hopping landing task to analyze the activation of their affected limbs versus control individuals in the vastus lateralis (VL), vastus medialis (VM), and biceps femoris (BF), Semitendinosus (ST) and gluteus maximus (Gmax), key muscle groups, were characterized by activation timing, activation duration and activation intensity. We hypothesized that the neuromuscular system of patients with ACL rupture for more than six months has undergone adaptive reorganization, which is manifested by early activation, prolonged activation duration, or enhanced activation intensity of certain muscles, to compensate for the effects of ACL deficiency on knee stability and to achieve landing kinematic patterns similar to those of healthy individuals.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Participant Recruitment\u003c/h2\u003e \u003cp\u003eThe study used G*Power 3.1 software for sample size estimation. The level of significance was set at α\u0026thinsp;=\u0026thinsp;0.05, and the target statistical power was 80%. Based on Cohen's recommendation\u003csup\u003e18\u003c/sup\u003e, the effect size (ES) was set at 0.46, and the minimum required sample size was calculated to be 40 individuals (20 in each group) using a two-way ANOVA model. Considering a dropout rate of approximately 10%, the final plan was to include 22 subjects in each group, for a total of 44, to ensure adequate statistical efficacy. All patients with ACL injuries completed testing before undergoing ACL reconstruction. Healthy individuals of the same sex, dominant leg side, and similar level of exercise (Tegner score not differing by more than \u0026plusmn;\u0026thinsp;1 point) were screened by questionnaire to serve as the control group. All participants signed informed consent forms prior to the experiment. All methods were carried out in accordance with relevant guidelines and regulations, including the Good Clinical Practice (GCP) guidelines and the Declaration of Helsinki. The study protocol was approved by the Ethics Committee of Sichuan Orthopedic Hospital (Ethics No. KY2020-017-01). The inclusion criteria were: injury group: 1) age 18\u0026ndash;35 years old; 2) mode of injury was non-contact injury; 3) the patient's injured leg was his/her dominant leg. We have determined that the patient's dominant leg did not change before or after the injury (the dominant leg is defined as the leg preferred for kicking, standing, jumping, or stepping on a box); 4) MRI showed a complete rupture of the ACL alone; 5) the duration of the disease was more than six months; 6) there was no injury to the adjacent joints; and 7) there was no underlying disease such as gout or rheumatoid arthritis. Control group: 1) Age: 18\u0026ndash;35 years old, regardless of gender; 2) No motor system diseases in the last six months; 3) No history of lower limb surgery.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Data collection\u003c/h2\u003e \u003cp\u003eIn this study, a QUALISYS 3D motion capture system (Model Oqus 300, Sweden) was synchronized with a Noraxon wireless surface EMG system (Model Ultium EMG, sampling frequency 2000 Hz, USA) and a Bertec force table (Model FP4060-08, sampling frequency 200 Hz, USA) for motion data acquisition. The force table was used to detect the initial contact (IC) time, defined as the instant when the vertical ground reaction force first exceeded 10N19. EMG acquisition sites were referenced to the SENIAM standardized localization guidelines\u003csup\u003e20\u003c/sup\u003e as detailed in Supplementary Table\u0026nbsp;1. Subjects underwent a 10-minute warm-up prior to testing, consisting of 5 minutes of jogging with 5 minutes of dynamic stretching. After warming up, the area to which the electrodes were attached was prepared by cleaning with 75% alcohol, shaving, exfoliating with fine sandpaper, and again cleaning with an alcohol cotton ball and air-drying to minimize skin surface impedance. Subsequently, silver/silver chloride electrodes (model CH3236, CATHAY, China) were affixed with an electrode spacing of 20 mm\u003csup\u003e21\u003c/sup\u003e, the reference electrode was kept equidistant from the acquisition electrode and secured against dislodgement by means of a muscle patch with medical adhesive tape (see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e)\u003csup\u003e22\u003c/sup\u003e. In my test procedure, the one-legged jump landing task was given first priority, followed by the maximal voluntary contraction (MVC) test, with a 5-minute rest period between the two. Subjects were asked to stand with their feet shoulder-width apart on a 30 cm raised platform, with the distance between the platform and the center of the force plate set at 80% of the distance from the subject's anterior superior iliac spine to the medial ankle\u003csup\u003e23\u003c/sup\u003e. The EMG signals were recorded before the start of the jump, and the subjects maintained a one-legged standing position on command, stabilized and jumped forward without initial velocity, and remained stationary for 3 seconds after landing on one foot. Each subject completed 5 tests at 1-minute intervals; no discomfort was experienced throughout the procedure (see Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Maximum voluntary contraction (MVC) testing was performed using the David isometric device, which measures the maximum flexion and extension forces of the anterior and posterior thigh muscle groups, respectively. For the gluteus maximus MVC test, the subject was lying prone on a yoga mat with the legs abducted about 30\u0026deg;, the knees flexed 90\u0026deg;, and the hip joint in 0\u0026deg; extension. The experimenter applied resistance to the lower and middle thighs with his bare hands, and the subject tried his best to complete the hip extension and abduction movements under the oral command, with the knee joint slightly off the ground (about 2\u0026ndash;3 cm) and holding it for 5 seconds\u003csup\u003e24\u003c/sup\u003e. All MVC tests were repeated 3 times at 30-second intervals with strong verbal encouragement to elicit maximal force output\u003csup\u003e25\u003c/sup\u003e. The MVC tests for the BF and ST muscles are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Data processing\u003c/h2\u003e \u003cp\u003ea. VL, VM, BF, ST, Gmax muscle activation timing metrics\u003c/p\u003e \u003cp\u003eThe raw surface electromyography (SEMG) signals were first visually inspected to ensure that the acquired data were complete and valid. Subsequently, the DC offset was removed using Noraxon Ultium EMG software and a fourth-order zero-delay Butterworth high-pass filter (cutoff frequency fc\u0026thinsp;=\u0026thinsp;15 Hz) was applied to remove motion artifacts. To extract temporal features of muscle activation, the filtered signal was full-wave rectified and a low-pass filter (fc\u0026thinsp;=\u0026thinsp;20 Hz) was applied to generate a linear envelope signal. By experimenting with cutoff frequencies in the range of 10\u0026ndash;25 Hz (in steps of 1 Hz), 20 Hz was finally selected as the low-pass filtering threshold, a parameter that maximizes the retention of key features consistent with changes in muscle tone\u003csup\u003e26\u003c/sup\u003e. The identification of muscle activation timing was based on a threshold of 15% of the maximum amplitude of the linear envelope signal: when 28 consecutive sampling points (sampling frequency 2000 Hz) exceeded or fell below this threshold, respectively, they were considered as the beginning and the end of muscle activation\u003csup\u003e27\u003c/sup\u003e. After several rounds of comparison and manual calibration in the range of 3%-25% thresholds, 15% was finally determined as the optimal threshold. All automatically extracted time points were visually verified manually to ensure that the analysis results accurately reflected the real muscle activation characteristics\u003csup\u003e28\u003c/sup\u003e. The final extracted temporal metrics included: the duration of muscle activation (ms); the time difference of activation onset time relative to initial contact (IC) (onset-IC, ms); and the time difference of peak EMG appearance time relative to IC (peak-IC, ms).\u003c/p\u003e \u003cp\u003eb. VL, VM, BF, ST, Gmax muscle activation strength indicators\u003c/p\u003e \u003cp\u003eRaw SEMG signals were full-wave rectified, smoothed using a moving-window (50 ms) root mean square (RMS) algorithm, and normalized by the peak value recorded during MVC. Muscle activation intensity indices were divided into the following two categories: preparatory muscle activity: peak and mean RMS values within a 100 ms window before IC; reactive muscle activity: peak and mean RMS values within a 100 ms window after IC.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Statistical analysis\u003c/h2\u003e \u003cp\u003eRaw data were entered and organized using Microsoft Excel, and statistical analysis was done using GraphPad Prism 9.5 software. All continuous variables were first assessed for normality by the Shapiro-Wilk test, and Levene's test for chi-square was used. For variables that satisfied both normal distribution and chi-square, a two-way ANOVA was used, with \"group\" (ACL injury group vs. control group) as a between-group factor and \"limb side\" (dominant vs. nondominant leg) as a within-group factor. If main effects or interactions were significant, post hoc two-by-two comparisons were further performed using Fisher's LSD method. Scheirer-Ray-Hare nonparametric tests were used for variables that did not meet the assumption of normality. All data are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation and the significance level was set at P\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Baseline characteristics of participants\u003c/h2\u003e\n \u003cp\u003eDuring the testing process, one subject in the injury group withdrew from the trial because she gave up ACL reconstruction surgery and chose conservative treatment; one subject in the control group was excluded because she was unable to complete all the tests due to scheduling conflicts. In the end, a total of 42 subjects completed all the tests, including 21 in the injury group and 21 in the control group. Among them, 22 were male and 20 were female. The basic information of the subjects is shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eBasic information of subjects\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eInjury group (N\u0026thinsp;=\u0026thinsp;21)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eControl group (N\u0026thinsp;=\u0026thinsp;21)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003et-value\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGender (M/F)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11/10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11/10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAge (y)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e26.97\u0026thinsp;\u0026plusmn;\u0026thinsp;4.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e24.66\u0026thinsp;\u0026plusmn;\u0026thinsp;3.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.861\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0702\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHeight (cm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e170.80\u0026thinsp;\u0026plusmn;\u0026thinsp;10.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e172.40\u0026thinsp;\u0026plusmn;\u0026thinsp;4.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.6298\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5324\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWeight (kg)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e68.03\u0026thinsp;\u0026plusmn;\u0026thinsp;12.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e72.47\u0026thinsp;\u0026plusmn;\u0026thinsp;8.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.366\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.1794\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBMI (kg/m2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22.67\u0026thinsp;\u0026plusmn;\u0026thinsp;2.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23.92\u0026thinsp;\u0026plusmn;\u0026thinsp;2.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.449\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.1552\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTegner Rating\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.14\u0026thinsp;\u0026plusmn;\u0026thinsp;1.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.29\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.3478\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.7298\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDuration of injury (months)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18.20\u0026thinsp;\u0026plusmn;\u0026thinsp;7.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Muscle activation duration\u003c/h2\u003e\n \u003cp\u003eSince no significant interaction effect was presented between subject group and test limb, the main effects of the group factor and limb factor were analyzed separately, and the results are shown in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. In terms of muscle activation duration, subject group showed a significant main effect on BF (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;4.732; P\u0026thinsp;=\u0026thinsp;0.0326), with the duration of activation of the dominant leg in the injury group being significantly longer than that of the dominant leg in the control group (P\u0026thinsp;=\u0026thinsp;0.0409). A significant main effect was also shown for Gmax (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;5.961; P\u0026thinsp;=\u0026thinsp;0.0168), which likewise showed a significantly longer duration of sustained activation of the dominant leg in the injury group (P\u0026thinsp;=\u0026thinsp;0.0469).\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"char\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDuration of sustained activation of each muscle comparison (ms)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"6\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eMuscle\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eInjury group\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eControl group\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003ep-valuea\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDominant leg (Affected limb)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNon-dominant leg\u003c/p\u003e\n \u003cp\u003e(Healthy limbs)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDominant leg\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNon-dominant leg\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e354.12\u0026thinsp;\u0026plusmn;\u0026thinsp;101.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e339.37\u0026thinsp;\u0026plusmn;\u0026thinsp;84.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e337.64\u0026thinsp;\u0026plusmn;\u0026thinsp;87.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e329.28\u0026thinsp;\u0026plusmn;\u0026thinsp;105.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.8781\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e336.45\u0026thinsp;\u0026plusmn;\u0026thinsp;77.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e322.16\u0026thinsp;\u0026plusmn;\u0026thinsp;80.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e311.22\u0026thinsp;\u0026plusmn;\u0026thinsp;82.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e321.59\u0026thinsp;\u0026plusmn;\u0026thinsp;86.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.4906\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e346.61\u0026thinsp;\u0026plusmn;\u0026thinsp;73.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e335.16\u0026thinsp;\u0026plusmn;\u0026thinsp;65.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e305.52\u0026thinsp;\u0026plusmn;\u0026thinsp;55.67*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e315.43\u0026thinsp;\u0026plusmn;\u0026thinsp;59.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.4472\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eST\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e347.34\u0026thinsp;\u0026plusmn;\u0026thinsp;66.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e338.24\u0026thinsp;\u0026plusmn;\u0026thinsp;65.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e311.34\u0026thinsp;\u0026plusmn;\u0026thinsp;57.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e319.97\u0026thinsp;\u0026plusmn;\u0026thinsp;54.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5084\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGmax\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e261.39\u0026thinsp;\u0026plusmn;\u0026thinsp;52.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e257.49\u0026thinsp;\u0026plusmn;\u0026thinsp;49.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e230.04\u0026thinsp;\u0026plusmn;\u0026thinsp;42.81*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e235.21\u0026thinsp;\u0026plusmn;\u0026thinsp;55.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.6808\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\"\u003eNote: \u003csup\u003ea\u003c/sup\u003e, indicates the effect of subject group\u0026times; test limb interactions on the muscle sustained activation time;*, indicates p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 for comparison (a), indicates the effect of subject group test limb interactions on the muscle sustained activation time;*, indicates p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 for comparison between the dominant leg in the injury group and the other groups.\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003e3. 3 Synchronization of myoelectric activity across muscles\u003c/h3\u003e\n\u003cp\u003eSince there was no significant interaction effect between subject group and test limb, the main effects of the two factors were analyzed separately in this section, and the results are shown in Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. In the comparison of onset-IC, the subject group showed a significant main effect on BF (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;5.127; P\u0026thinsp;=\u0026thinsp;0.0351), with onset-IC for the dominant leg in the injury group significantly earlier than that for the control group\u0026apos;s dominant leg (P\u0026thinsp;=\u0026thinsp;0.0457).ST also showed a significant main effect (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;6.314; P\u0026thinsp;=\u0026thinsp;0.0239), with the onset-IC of the dominant leg in the injury group being significantly earlier than that of the dominant leg in the control group (P\u0026thinsp;=\u0026thinsp;0.0277) and that of its own non-dominant leg (P\u0026thinsp;=\u0026thinsp;0.0405). In addition, Gmax also showed a significant main effect (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;4.053; P\u0026thinsp;=\u0026thinsp;0.0474), as evidenced by a significantly earlier onset-IC in the dominant leg of the injury group than in the dominant leg of the control group (P\u0026thinsp;=\u0026thinsp;0.0192). In the comparison of peak-IC, BF showed a significant main effect (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;4.040; P\u0026thinsp;=\u0026thinsp;0.0415), in which the peak-IC of the dominant leg in the injury group was significantly later than that of the dominant leg in the control group (P\u0026thinsp;=\u0026thinsp;0.0457).ST also showed a significant main effect (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;7.271; P\u0026thinsp;=\u0026thinsp;0.0190), with the dominant leg in the injury group having the peak-IC significantly later than the control dominant leg (P\u0026thinsp;=\u0026thinsp;0.0280).\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"char\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eComparison of onset-IC and peak-IC by muscle (ms)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"7\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eMuscle\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eInjury group\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eControl group\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003ep-valuea\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDominant leg\u003c/p\u003e\n \u003cp\u003e(Affected limb)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNon-dominant leg\u003c/p\u003e\n \u003cp\u003e(Healthy limbs)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDominant leg\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNon-dominant leg\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eonset-IC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-125.37b\u0026thinsp;\u0026plusmn;\u0026thinsp;45.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-118.35\u0026thinsp;\u0026plusmn;\u0026thinsp;42.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-109.62\u0026thinsp;\u0026plusmn;\u0026thinsp;43.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-114.26\u0026thinsp;\u0026plusmn;\u0026thinsp;41.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5398\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-120.84\u0026thinsp;\u0026plusmn;\u0026thinsp;37.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-114.66\u0026thinsp;\u0026plusmn;\u0026thinsp;35.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-109.57\u0026thinsp;\u0026plusmn;\u0026thinsp;30.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-103.36\u0026thinsp;\u0026plusmn;\u0026thinsp;34.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9985\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-150.55\u0026thinsp;\u0026plusmn;\u0026thinsp;66.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-136.83\u0026thinsp;\u0026plusmn;\u0026thinsp;63.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-112.86\u0026thinsp;\u0026plusmn;\u0026thinsp;55.67*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-129.28\u0026thinsp;\u0026plusmn;\u0026thinsp;54.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.2544\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eST\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-156.59\u0026thinsp;\u0026plusmn;\u0026thinsp;66.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-117.49\u0026thinsp;\u0026plusmn;\u0026thinsp;59.10*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-114.49\u0026thinsp;\u0026plusmn;\u0026thinsp;60.71*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-120.41\u0026thinsp;\u0026plusmn;\u0026thinsp;56.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0938\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGmax\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-95.61\u0026thinsp;\u0026plusmn;\u0026thinsp;20.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-87.79\u0026thinsp;\u0026plusmn;\u0026thinsp;17.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-82.16\u0026thinsp;\u0026plusmn;\u0026thinsp;18.36*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-85.21\u0026thinsp;\u0026plusmn;\u0026thinsp;16.77\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.1760\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003epeak-IC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e151.26\u0026thinsp;\u0026plusmn;\u0026thinsp;46.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e161.37\u0026thinsp;\u0026plusmn;\u0026thinsp;48.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e148.41\u0026thinsp;\u0026plusmn;\u0026thinsp;52.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e133.63\u0026thinsp;\u0026plusmn;\u0026thinsp;57.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.2701\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e146.64\u0026thinsp;\u0026plusmn;\u0026thinsp;59.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e148.22\u0026thinsp;\u0026plusmn;\u0026thinsp;65.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e157.80\u0026thinsp;\u0026plusmn;\u0026thinsp;74.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e160.71\u0026thinsp;\u0026plusmn;\u0026thinsp;70.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9643\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-34.21\u0026thinsp;\u0026plusmn;\u0026thinsp;12.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-40.31\u0026thinsp;\u0026plusmn;\u0026thinsp;16.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-42.83\u0026thinsp;\u0026plusmn;\u0026thinsp;10.38*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-37.25\u0026thinsp;\u0026plusmn;\u0026thinsp;13.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0578\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eST\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-32.15\u0026thinsp;\u0026plusmn;\u0026thinsp;12.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-38.14\u0026thinsp;\u0026plusmn;\u0026thinsp;13.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-40.36\u0026thinsp;\u0026plusmn;\u0026thinsp;11.33*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-38.34\u0026thinsp;\u0026plusmn;\u0026thinsp;9.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.1267\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGmax\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e41.47\u0026thinsp;\u0026plusmn;\u0026thinsp;12.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e39.26\u0026thinsp;\u0026plusmn;\u0026thinsp;12.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40.08\u0026thinsp;\u0026plusmn;\u0026thinsp;10.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37.82\u0026thinsp;\u0026plusmn;\u0026thinsp;12.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9924\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\"\u003eNote: \u003csup\u003ea\u003c/sup\u003e, indicates the effect of subject group\u0026times; test limb interactions on the onset-IC and peak-IC time of muscle; \u003csup\u003eb\u003c/sup\u003e, negative values indicate that they occurred before initial contact (IC); *, indicates p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 for comparison of the dominant leg in the injury group versus the other groups.\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003ch3\u003e3. 4 Characterization of EMG activation intensity by muscle\u003c/h3\u003e\n\u003cp\u003eFor the RMS peak versus mean within 100 ms before and after IC, there was no significant interaction effect between subject group and test limb, so the main effect of subject group versus test limb was analyzed, as shown in Figs. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. Specific P values for the multiple comparisons results are detailed in Supplementary Table\u0026nbsp;2. There was a significant main effect of subject group on the peak RMS of the VL within 100 ms after IC (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;4.742; P\u0026thinsp;=\u0026thinsp;0.0324), and the dominant leg in the injury group was significantly lower than the dominant leg in the control group (P\u0026thinsp;=\u0026thinsp;0.0171). There was a significant main effect of subject group on the peak RMS of VM within 100 ms after IC (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;6.007; P\u0026thinsp;=\u0026thinsp;0.0164), with the dominant leg in the injury group being significantly lower than the dominant leg in the control group (P\u0026thinsp;=\u0026thinsp;0.0054) and the non-dominant leg in the control group (P\u0026thinsp;=\u0026thinsp;0.0253). There was a significant main effect of subject group on the mean RMS of VM within 100 ms after IC (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;6.925; P\u0026thinsp;=\u0026thinsp;0.0102), which was significantly lower for the dominant leg in the injury group (P\u0026thinsp;=\u0026thinsp;0.0178) and the nondominant leg in the injury group (P\u0026thinsp;=\u0026thinsp;0.0357) than for the dominant leg in the control group. There was a significant main effect of subject group on the peak RMS of ST within the first 100 ms of IC (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;6.429; P\u0026thinsp;=\u0026thinsp;0.0132), which was significantly higher in the dominant leg of the injury group than in the dominant leg of the control group (P\u0026thinsp;=\u0026thinsp;0.0439) and the non-dominant leg of the control group (P\u0026thinsp;=\u0026thinsp;0.0229). There was a significant main effect of subject group on the mean RMS of ST within the first 100 ms of IC (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;5.563; P\u0026thinsp;=\u0026thinsp;0.0208), and the dominant leg was significantly higher in the injury group than the dominant leg in the control group (P\u0026thinsp;=\u0026thinsp;0.0483). There was a significant main effect of subject group on the peak RMS of Gmax within 100 ms after IC (F\u003csub\u003e(1,40)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;13.94; P\u0026thinsp;=\u0026thinsp;0.0004), with the dominant leg in the injury group being significantly lower than the dominant leg in the control group (P\u0026thinsp;=\u0026thinsp;0.0003) and the nondominant leg in the control group (P\u0026thinsp;=\u0026thinsp;0.0122), and the nondominant leg in the injury group being significantly lower than the dominant leg in the control group (P\u0026thinsp;=\u0026thinsp;0.0081).\u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eACL disruption is thought to disrupt pre-existing neuromuscular control strategies in the lower extremity. It has been shown that ACL injury can cause significant alterations in the kinematic, kinetic, and electromyographic characteristics of the lower extremity during high-impact tasks such as jump landings, and that these changes reflect a phenomenon of neuromuscular adaptation or reprogramming in response to joint instability aimed at enhancing the dynamic stability of the knee and reducing the risk of re-injury by modulating the order of activation, duration, and peak response.\u003c/p\u003e \u003cp\u003eIn the present study, we found that muscle activation durations were generally prolonged in the dominant leg of the ACL-injured group during a single-leg jump landing task, with BF and Gmax being the most significant. This result is consistent with previous findings regarding prolonged EMG durations in walking, such that the VM, VL, semitendinosus, and lateral popliteus showed similar trends \u003csup\u003e29,30\u003c/sup\u003e. The prolonged activation duration may represent a compensatory strategy for knee instability, increasing joint compressive forces by maintaining longer muscle contractions, thereby enhancing mechanical stability and compensating for limitations caused by ACL deficits, resulting in a kinematic profile similar to that of the healthy side. In terms of muscle activation timing, the present study observed that the onset of activation (onset-IC) of several key muscle groups in the ACL-injured group was significantly earlier than that of the control group, especially the posterior masseter muscles (BF, ST) and Gmax. This early pre-activation pattern was considered as part of the \"pretension conditioning\" during landing, which aims to By preactivating the muscles a sufficiently stable base prior to contact with the ground to control knee trajectory and absorb ground reaction forces. In the case of the quadriceps muscle, for example, it has been shown that healthy individuals preactivate the VM and VL 103\u0026ndash;114 ms before ground contact, and the injury group in this study showed a similar or even earlier activation sequence. In addition, there is an electromechanical delay (EMD) between the EMG signal and actual tension generation, which ranges from 20\u0026ndash;100 ms for knee extensors\u003csup\u003e31\u003c/sup\u003e and may reach 55\u0026ndash;92 ms for hamstrings\u003csup\u003e32\u003c/sup\u003e, making early activation particularly critical. Analysis of the time of peak EMG appearance (peak-IC) revealed that both BF and ST peaks were significantly delayed in the ACL injury group, which is highly consistent with the popliteal mechanism of action. The hamstrings are the main co-stabilizing muscles of the ACL by generating tibial \"posterior drawer force\" to resist anterior displacement. During landing maneuvers, peak tibiofemoral shear occurs approximately 28\u0026ndash;30 ms after touchdown\u003csup\u003e26,27\u003c/sup\u003e. Therefore, a delay in maximal hamstring output to this stage coincides with the most vulnerable window of the ACL, thus forming a dynamic protective barrier. Blackburn et al.\u003csup\u003e32\u003c/sup\u003e state that hamstring EMD is 72 ms, which is highly consistent with the result that hamstrings reach peak activity approximately 30\u0026ndash;40 ms before touchdown. This is highly consistent with the result that the hamstrings reach peak activity around 30\u0026ndash;40 ms before touchdown. Further, Gmax showed a similar pattern of regulation. Not only was Gmax activated earlier before touchdown in the ACL injury group, its peak activation also occurred around 40 ms after landing, and the abduction moment generated by Gmax was expected to peak 92 ms after landing. This coincides with the electromechanical delay (52 ms on average) in hip abduction proposed by Kim et al.\u003csup\u003e33\u003c/sup\u003e, suggesting that its abduction output is functioning right at the peak tibiofemoral shear force phase. It has been reported that the peak knee valgus angle mostly occurs 85 ms after landing (range 70\u0026ndash;100 ms), and more than 60% of athletes reach their maximal knee valgus angle at this stage\u003csup\u003e34,35\u003c/sup\u003e. Therefore, early activation of Gmax helps to counteract the tendency of hip adduction and knee valgus and prevents pelvic instability from adversely affecting the knee joint. Overall, patients with ACL injuries show a typical \"pre-activation-post-peak\" bi-directional strategy in landing tasks: key muscle groups are activated early to pre-establish muscle tone in response to ground impact, and the peak is moderately delayed to match the timing of the peak of the ground reaction force and the emergence of shear forces, thus maximizing their ability to respond to ground impact. This adaptation pattern not only reflects the reorganization of the neuromuscular control system in the context of injury, but also provides an important biomechanical basis for preoperative patient rehabilitation assessment and intervention design.\u003c/p\u003e \u003cp\u003eIn the ACL-injured group, the peak EMG values of the quadriceps muscles (VL, VM) were significantly lower than those of the healthy control group within 100 ms after landing, suggesting that the activation of the knee extensor muscles during the touchdown phase was reduced. This feature is referred to as the \"quadriceps avoidance strategy\", reflecting the fact that patients may actively reduce extensor output to avoid knee instability, which affects joint braking and postural control\u003csup\u003e36\u003c/sup\u003e. In contrast, the hamstrings showed a tendency to increase activation, especially ST, which peaked significantly within 100 ms before touchdown, and BF, which tended to increase both before and after touchdown. As a co-stabilizing muscle of the ACL, popliteus mainly limits anterior translation and internal rotation by generating tibial posterior moment, and its enhanced recruitment contributes to knee stability and compensates for the lack of ACL function. This feature fits with the electromechanical delay time of the hamstrings, which ensures the provision of an effective response during the peak phase of shear\u003csup\u003e30\u003c/sup\u003e. Gmax, although showing a reduced peak after landing in the injury group, has an earlier onset and longer duration, suggesting that it compensates through temporal regulation to maintain hip and pelvic stability. Hamstrings take on more loads when the function of Gmax is reduced, and their enhanced activation may also partly stem from the indirect compensation for gluteal insufficiency\u003csup\u003e37\u003c/sup\u003e. In addition, ACL injury may interfere with central drive, resulting in decreased efficiency of motor unit recruitment, further exacerbating Gmax underactivation\u003csup\u003e38\u003c/sup\u003e. Overall, the ACL-injured group showed an activation pattern of \"extensor inhibition - flexor strengthening - gluteal sequential compensation\", which reflects the self-regulation mechanism of the neuromuscular system under the condition of impaired joint stability. The results suggest that hamstring and gluteal muscle training should be emphasized in preoperative rehabilitation to optimize the stability of the kinetic chain and reduce the risk of landing-related injuries.\u003c/p\u003e \u003cp\u003eThe relatively limited sample size of this study, which included only 21 patients with ACL injury and 21 healthy controls, and the age concentration of subjects in younger age groups may limit the generalizability of the findings. Future studies may expand the sample size and introduce subjects of different age groups to enhance the representativeness and external validity of the findings. In addition, the affected limbs of all patients with ACL injuries in this study were dominant legs, failing to explore the potential effects of limb dominance on EMG activation patterns. Therefore, follow-up studies are recommended to include a comparison of dominant versus nondominant legs in their design to further clarify the mechanism of limb laterality in neuromuscular control.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eIn a single-leg jump landing task, patients with ACL injuries of an average disease duration of 18 months generally had a prolonged muscle activation duration, reflecting compensatory mechanisms to maintain kinematic stability, despite a preactivation sequence consistent with that of healthy individuals. Preactivation of the biceps femoris, semitendinosus, and gluteus maximus muscles in the affected limb occurred with delayed hamstring peaks, possibly enhancing knee stability by enhancing posterior tibial shift control and resisting excessive anterior translation and internal rotation.\u003c/p\u003e "},{"header":"Declarations","content":"\u003ch2\u003eConflict of interest:\u003c/h2\u003e \u003cp\u003eThe authors do not have any potential conflicts of interest.\u003c/p\u003e \u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eNo funding.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eJ.X. and M.C. designed the research. J.X. and J.R. collected, analyzed the data, and drafted the manuscript. J.X. and XB. L. revised the manuscript. All authors contributed to the article and approved the submitted version.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors express gratitude to all participants.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data supporting the findings of this study are available from the corresponding author upon reasonable request\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003e\u003cspan\u003eGriffin, L. Y. et al. Understanding and preventing noncontact anterior cruciate ligament injuries: a review of the Hunt Valley II meeting, January 2005. \u003cem\u003eAM J SPORT MED\u003c/em\u003e 34 1512 (2006).\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eNordenvall, R. et al. 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Muscle fatigue in the gluteus maximus changes muscle synergies during single-leg landing. \u003cem\u003eJ BODYW MOV THER\u003c/em\u003e 27 493 (2021).\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eTrulsson, A., Miller, M., Hansson, G., Gummesson, C. \u0026amp; Garwicz, M. Altered movement patterns and muscular activity during single and double leg squats in individuals with anterior cruciate ligament injury. \u003cem\u003eBMC MUSCULOSKEL DIS\u003c/em\u003e 16 28 (2015).\u003c/span\u003e\u003c/li\u003e\n\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":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"ACL, noncontact injury, surface electromyography, rehabilitation, isometric muscle strength, root mean square amplitude","lastPublishedDoi":"10.21203/rs.3.rs-6633756/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6633756/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThere have been many studies on neuromuscular adaptation after anterior cruciate ligament (ACL) reconstruction, while the understanding of muscle activation patterns in unreconstructed patients with ACL rupture is still limited. The aim of this study was to investigate the lower limb electromyographic characteristics of unreconstructed patients with complete ACL rupture in a single-legged hopping landing task in order to deepen the understanding of motor control strategies in the ACL-deficient state and to provide a reference for rehabilitation assessment and intervention. Forty-two subjects were recruited for this study using a case-control design, with an ACL injury group (n\u0026thinsp;=\u0026thinsp;21) of patients with unilateral non-contact complete rupture without reconstruction and a control group (n\u0026thinsp;=\u0026thinsp;21) of healthy individuals matched for gender, dominant leg, and level of exercise. All subjects completed a single-leg hop landing task and synchronized Noraxon Ultium surface EMG signals with Bertec force plate data via the QUALISYS 3D motion capture system. EMG data were recorded from the lateral femoral (VL), medial femoral (VM), biceps femoris (BF), semitendinosus (ST), and gluteus maximus (Gmax) muscles before and after the landing for 100 ms each. Calculated metrics included activation onset time (onset-IC), peak appearance time (peak-IC), activation duration, and standardized root mean square (RMS) values. Data were analyzed by two-way ANOVA or nonparametric Scheirer-Ray-Hare test, and the significance level was set at P\u0026thinsp;\u0026lt;\u0026thinsp;0.05. BF (P\u0026thinsp;=\u0026thinsp;0.0409) and Gmax (P\u0026thinsp;=\u0026thinsp;0.0469) sustained activation of the dominant leg in the injury group was significantly longer than that of the dominant leg in the control group. The onset-IC of BF (P\u0026thinsp;=\u0026thinsp;0.0457), ST (P\u0026thinsp;=\u0026thinsp;0.0277), and Gmax (P\u0026thinsp;=\u0026thinsp;0.0192) of the dominant leg in the injury group was significantly earlier than that of the dominant leg in the control group. The peak-IC of BF (P\u0026thinsp;=\u0026thinsp;0.0457) and ST (P\u0026thinsp;=\u0026thinsp;0.0280) of the dominant leg in the injury group was significantly later than that of the dominant leg in the control group. The peak RMS of VL (P\u0026thinsp;=\u0026thinsp;0.0171), VM (P\u0026thinsp;=\u0026thinsp;0.0054), and Gmax (P\u0026thinsp;=\u0026thinsp;0.0003) in the dominant leg of the injury group was significantly lower than that of the dominant leg of the control group in 100 ms after IC. Unreconstructed patients, averaging 18 months after ACL injury, continued to maintain a similar muscle pre-activation sequence as healthy individuals during the jump landing task, but showed a prolonged activation duration and reduced activation intensity, suggesting that neuromuscular activity was adjusted to maintain the kinematic profile. The delay in the peak of the posterior muscle groups (especially BF and ST) may be used to synergize tibial rearward movement and reduce forward movement and internal rotation, thus constituting a compensatory protective mechanism. The results of this study provide evidence for neuromuscular adaptation in the ACL-deficient state and are informative for preoperative functional assessment and rehabilitation intervention strategies.\u003c/p\u003e","manuscriptTitle":"Lower extremity electromyographic characteristics of patients with noncontact complete anterior cruciate ligament rupture not reconstructed in one-legged jump landings: a case-control study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-09 08:32:20","doi":"10.21203/rs.3.rs-6633756/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-09-17T06:40:01+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-13T14:17:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"264242944900521221514566795008912509979","date":"2025-08-17T13:23:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"57701967927717635627810400249758141580","date":"2025-08-16T17:57:44+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"323264324840219825909273090276018161448","date":"2025-07-16T03:40:25+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-25T06:08:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"96431051891494339825888161290881571815","date":"2025-06-05T05:02:42+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-02T22:43:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-02T04:32:07+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-21T02:44:56+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-05-21T02:43:46+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"cbdfe8e8-200f-4038-bc3c-5767b7132a1a","owner":[],"postedDate":"June 9th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":49475302,"name":"Health sciences/Health care/Disease prevention"},{"id":49475303,"name":"Health sciences/Health care/Therapeutics/Rehabilitation"},{"id":49475304,"name":"Health sciences/Risk factors"}],"tags":[],"updatedAt":"2025-12-01T16:14:32+00:00","versionOfRecord":{"articleIdentity":"rs-6633756","link":"https://doi.org/10.1038/s41598-025-29516-y","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-11-28 15:58:36","publishedOnDateReadable":"November 28th, 2025"},"versionCreatedAt":"2025-06-09 08:32:20","video":"","vorDoi":"10.1038/s41598-025-29516-y","vorDoiUrl":"https://doi.org/10.1038/s41598-025-29516-y","workflowStages":[]},"version":"v1","identity":"rs-6633756","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6633756","identity":"rs-6633756","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}