Effects of muscle strength training combined with neuromuscular electrical stimulation on pain, function, muscle strength, patellar stress, and muscle activation during running in people with patellofemoral pain

Effects of muscle strength training combined with neuromuscular electrical stimulation on pain, function, muscle strength, patellar stress, and muscle activation during running in people with patellofemoral pain | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effects of muscle strength training combined with neuromuscular electrical stimulation on pain, function, muscle strength, patellar stress, and muscle activation during running in people with patellofemoral pain Jing Wu, Yingce Yao, Xia Wang, Jianbin Zhao, Chen Yang, Xiaoyu Wang, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7611495/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 14 You are reading this latest preprint version Abstract Objective This study aimed to investigate the effects of a 6-week muscle strength training combined with neuromuscular electrical stimulation on pain, function level, muscle strength, patellar stress, and muscle activation during running among individuals with patellofemoral pain (PFP). Methods This study is a randomized, controlled, and assessor-blinded trial. Fifty-eight PFP participants were randomly assigned to the neuromuscular electrical stimulation combined with muscle strength training (EMS), conventional muscle strength training (MST) and health education (HE) groups. They received EMS, MST and health lectures series, respectively, for 6 weeks. Pain scores, knee function levels of anterior knee pain scale (AKPS), muscle strength of quadriceps, patellofemoral joint stress (PFJ), and muscle activation of vastus medialis oblique (VMO) and vastus lateralis (VL) during running were measured at week 0 and week 7, respectively. Two-way (group by time) ANOVA with repeated measures was used to evaluate training effects. Results Significant interactions were detected in pain score, AKPS, muscle strength, PFJ and muscle activation of VMO and VL. Compared with week 0, the pain score and PFJ decreased, whereas the AKPS, quadriceps muscle strength, muscle activation of VMO and VMO:VL ratio increased in EMS and MST groups at week 7. Additionally, the AKPS and muscle activation of VMO:VL ratio were significantly increased in the EMS group at week 7 compared with the MST and HE groups. Conclusion EMS could be recommended as one of the clinical treatments for PFP to relieve pain, improve knee function, and balance muscle activation of VMO and VL, thereby decrease patellofemoral joint stress during running. Trial registration: The effects of muscle electrical stimulation combined with muscle training on patients with joint pain and biomechanical characteristics of lower limbs, ChiCTR2300067598. Registered 13 January 2023, https://www.chictr.org.cn/showproj.html?proj=180778 Anterior knee pain Rehabilitation Electrical stimulation Patellofemoral joint stress Figures Figure 1 Figure 2 Figure 3 Background Patellofemoral pain (PFP) is a prevalent musculoskeletal condition among young individuals, characterized by insidious pain not attributable to trauma or identifiable pathology [ 1 ] . The hallmark of PFP is intermittent pain, provoked by activities that elevate stress on the patellofemoral joint, such as prolonged sitting with flexed knees, running, stair climbing, and squatting [ 2 ] . Although PFP is often regarded as a self-limiting condition, evidence suggests that its symptoms frequently persist for years [ 3 ] . This chronic pain not only adversely affects an individual's physical activity levels and quality of life, but also heightens the risk of developing knee osteoarthritis over time [ 4 ] . Elevated patellofemoral joint stress (PFJS) represents a primary pathological mechanism underlying PFP [ 5 ] . Abnormal patellar tracking leads to stress concentration on subchondral bone, accelerating cartilage degeneration and resulting in pain [ 6 – 8 ] . Quadriceps muscle imbalance and hip muscle weakness are key biomechanical contributors to increased PFJS [ 9 – 11 ] . Specifically, imbalances and abnormal activation between the vastus medialis oblique (VMO) and vastus lateralis (VL) disrupt patellar stability, causing abnormal lateral tension, and altering patellar tracking and joint loading distribution. Weakness in the hip abductor and external rotator muscles impair femoral control, leading to increased dynamic knee valgus during functional activities and a significantly rise in PFJS [ 11 – 13 ] . Consequently, strengthening both hip and knee muscles, particularly by improving quadriceps balance and hip muscle control, which is crucial intervention for reducing PFJS and lowering the risk of injury. Strength training is a critical component of the PFP rehabilitation programs, designed to alleviate pain and enhance function, typically targeting on strengthening the quadriceps and gluteal muscles. Research indicates [ 14 – 16 ] that strengthening hip and knee muscles not only alleviates pain but also enhances physical function, including improved posture control, increased pelvic stability, and reducing joint loading during running. However, conventional strength training approaches require refinement to effectively address strength imbalances in VMO and VL, which may contribute to abnormal patellar tracking during movement and symptom recurrence [ 17 ] . Consequently, current rehabilitation programs require further optimization to more effectively mitigate this issue. Neuromuscular electrical stimulation (NMES) is an established adjunctive therapeutic approach for the neuromuscular rehabilitation of atrophied or weakened muscles [ 18 , 19 ] . NMES not only alleviates pain but also enhances the function of targeted muscles, activates muscle fibers challenging to engage through conventional training, and promotes to comprehensive muscle strength improvement [ 18 , 20 ] . Conventional quadriceps strengthening exercises may not effectively activate the vastus medialis muscle, resulting in challenges in correcting the strength imbalance between the VMO and VL [ 17 ] . Therefore, integrating NMES to activate the VMO during strength training may facilitate improved balance of strength between the VMO and VL, optimizing the patellofemoral joint trajectory during movement, reducing joint stress, and ultimately achieving pain and enhancing lower limb function. This study aims to investigate the effects of a 6-week intervention involving NMES combined with strength training (EMS) on pain, function, muscle strength, patellar stress, and muscle activation during running in people with PFP. The study hypothesizes that: (1) Both the EMS group and the muscle strength training (MST) group will effectively alleviate pain, enhance functional outcomes, increase knee extensor strength, and reduce PFJS during running. (2) Compared with the MST group and the health education (HE) group, the EMS group will demonstrate greater improvements in alleviating pain, reducing PFJS during running, increasing activation of the VMO, and enhancing functional outcomes and knee extensor strength. Methods Sample-size calculating Sample size was determined through power analysis using the G*Power software (Version 3.1.9.6, Franz Faul, University of Kiel, Germany), based on previous research [ 21 ] involving a six-week standardized muscle strength training combined with neuromuscular electrical stimulation therapy for 27 PFP patients. By comparing the Anterior Knee Pain Scale (AKPS) scores of PFP patients in the experimental group before and after the intervention (increased from 60.4 ± 14.8 to 73.0 ± 14.3), with a significance level of α = 0.05, Type II error β = 0.20, and power (1-β) = 0.80, the minimum sample size was calculated as n = 13. Considering a potential dropout rate of 20%, each group in this study was determined to require at least 16 subjects. Participant recruitment All participants were between the ages of 18 and 35 years. Participants with PFP recruited for this study met the following criteria [ 22 ] :(1) prepatellar or retropatellar knee pain following at least two of the following activities— prolonged sitting, stair climbing, squatting, running, kneeling, jumping, and deep knee flexion with resisted knee extension; (2) insidious onset of symptoms unrelated to trauma; and (3) pain persisting for a minimum of three months. Exclusion criteria [ 22 , 23 ] included: (1) other knee disorders, including meniscal or other intra-articular injuries, a history of recurrent patellar subluxation or dislocation, or prior knee surgery; and (2) contraindications to low-frequency electrotherapy or inability to tolerate electrical stimulation. After receiving trial information from a physical therapist and being given at least 24 hours to consider participation, the investigator obtained written informed consent and scheduled trial visits. The knee with the most severe symptoms at baseline was designated as the study knee. All participants were recruited through posted flyers in the Shandong Sport University, athletic health clubs, and local sports training center. All potential participants were screened by a licensed physical therapist to assess eligibility based on the inclusion and exclusion criteria. Those who met the criteria were consecutively enrolled and reported to the Biomechanics Laboratory at Shandong Sport University for testing. Participants provided written informed consent, and the study was approved by the Shandong Sport University Committee for Human Investigations (2022012), registered with the Chinese Clinical Trial Registry (registration number: ChiCTR2300067598). and conducted in accordance with the Declaration of Helsinki. Randomization and allocation The study included 72 eligible participants enrolled in the trial. To achieve concealed allocation and simple randomization, a researcher not involved in patient recruitment or treatment employed the RAND function in Microsoft Excel to generate random numbers prior to data collection. Based on these numbers, the 72 participants who met the trial criteria were matched according to general characteristics such as age, height, weight, and gender, and then allocated to one of three groups: the electrical stimulation combined with muscle strength training group (EMS), the muscle strength training group (MST), and the health education group (HE), with 24 participants in each group. At week 0 (within one week prior to the intervention) and week 7 (within one week after the intervention), the affected lower extremity of each participant was assessed using standardized measures. In cases where both knees were symptomatic, the more severely affected side was selected for evaluation. During the 6-week intervention, attendance was monitored by designated personnel. To maintain scientific rigor, participants with attendance rates below 85%, those who received additional treatments during the intervention period, or those who experienced accidental injuries outside of the intervention were excluded. Ultimately, 58 participants completed the study: 20 in each of the EMS and MST groups, and 18 in the HE Group (Fig. 1 ). Interventions The treatment regimen for both the MST and EMS groups consisted of 18 sessions over a 6-week period (3 sessions per week), each supervised by an experienced clinical physiotherapist. The primary aim was to avoid pain during all exercises and to prevent abnormal movement patterns or engagement in additional unsanctioned physical activities. The physiotherapist assisted each participant during the sessions, supervising and correcting t posture before and during the execution of each exercise, and providing corrective feedback as needed. Following the recommendations of the American College of Sports Medicine (ACSM) [ 24 ] , each session followed predetermined phases: a warm-up, a main training component, and a concluding cool-down with stretching. The warm-up phase comprised dynamic lower extremity exercises designed to increase blood flow, raise muscle temperature, and activate the central nervous system. Plyometric training included bodyweight or resistance-based strength exercises targeting the quadriceps, gluteus maximus, and gluteus medius muscles. Each session incorporated 4–5 selected movements (Fig. 2 ), lasting 40 to 60 minutes. Perform each movement three times with 60-second rests between sets. Training was performed three times a week, following progressive overload principles and including individualized adjustments to training load intensity. Load was standardized at 70% of each individual’s estimated 1-repetition maximum (1RM) capacity [ 25 ] . Each session concluded with full-body stretching and lower extremity relaxation. Participants in the EMS group performed the same supervised exercise program as those in the MST group. In addition, reusable, self-adhesive electrode pads were placed on the VMO of the affected leg prior to plyometric training, and electrical stimulation was superimposed on knee extensor muscles contractions to facilitate activation and strengthen the VMO. The electrodes were positioned along the muscle fibers, with the cathode placed 4 cm above and 3 cm medial to the patella, and the anode positioned 10 cm above the patella and medial to the mid-thigh line. Using a Digitimer DS7AH (Digitimer Ltd ., Welwyn Garden City, UK), participants received individually adjusted maximum permissible intensities [ 19 ] . The NMES parameters were set as follows: a square waveform with a pulse width of 400 µs, frequency of 50 Hz, pulse duration of 250 µs, and a work-rest cycle of 10–50 seconds. The stimulation current was maintained below 100 mA [ 20 ] . To accommodate the progressive increase in participant tolerance, stimulation intensity was adjusted every two weeks to optimize motor unit recruitment [ 26 ] . 9/19/2025 Participants in the HE group did not receive any exercise intervention but attended weekly educational sessions focused on strategies to protect the knee from injury during running and daily activities. Additionally, educational articles about PFP management were distributed online. The health education program also lasted 6 weeks. Participants were instructed not to engage in any exercise program or therapeutic intervention during this period, and exercise training could be initiated after the 6-week control phase. Outcome measures Pain Pain score was measured using a visual analog scale (VAS), which quantifies the highest level of pain experienced during activity in the previous week. During the assessment, participants marked their perceived pain level on a 10 cm VAS, where 0 indicated “no pain” and 10 represented “worst imaginable pain”. The distance from the left anchor point to the participant's mark was recorded as the pain score [ 27 ] . Function Self-reported knee function was assessed using the Anterior Knee Pain Scale (AKPS) [ 28 ] , a 13-item questionnaire addressing symptoms and functional limitations such as stair climbing, walking, running, jumping, and prolonged sitting. The AKPS score ranges from 0 to 100, with lower scores representing greater functional impairment. Muscle strength Isokinetic muscle strength of the affected limb was assessed using the IsoMed 2000 isokinetic dynamometer (D&R Ferstl GmbH, Hemau, Germany). Participants were seated in a stable position with immobilization straps to prevent compensatory trunk movements. The axis of rotation of the device was aligned with the knee joint and gravity compensation was applied. Prior to testing, participants performed five practice contractions to become familiar with the procedure and to ensure proper strap placement on the torso, lower back, and thighs, minimizing compensatory movements at adjacent joints. After a 5-minute rest, isokinetic torque of the quadriceps was measured at an angular velocity of 60°/s during continuous, bidirectional knee flexion-extension movements [ 29 ] . Participants exerted maximal force as rapidly as possible to familiarize themselves with the task and ensure consistent force production during the formal trials. Each participant completed the test a minimum of three times. Biomechanical data collection Participants were instructed to wear standardized tights and running shoes, complete a 10-minutes warm-up, and familiarize themselves with the test procedures. Following the warm-up, 41 reflective markers were affixed to the participant’s body based on surface anatomical landmarkers. Electrode placement sites for the VMO and VL muscles on the affected lower limb were also determined. Prior to electrode application, the skin at each placement site was shaved, cleansed with alcohol, lightly abraded, and cleaned using a medical abrasive paste to reduce impedance. Bipolar Ag-AgCl surface electrodes with a 10-mm interelectrode distance were applied to the target muscles to record muscle activity. Electrode placement followed the guidelines of the Surface Electromyography for the Non-Invasive Assessment of Muscles (SENIAM) [ 30 ] . Participants then stood in the anatomical position to undergo a 5-second static calibration. After calibration, they moved to the starting point of a simulated running track, located 8 meters from the force platform. Participants ran at a self-selected speed using a heel-to-toe running pattern and completed a foot strike with the affected leg on the force platform. Each participant completed three successful trials, with 1–2 minutes of rest between each. The entire running process was performed without any pace adjustment, with movement being natural and continuous. Data collection was conducted using a 12-camera Vicon motion capture system (Nexus 12.0, Vicon Motion Systems, Oxford, UK) at a sampling frequency of 100 Hz to capture 3D marker trajectories. Ground reaction forces were collected at 1000 Hz using an AMTI force platform (AMTI, Inc., Watertown, MA, USA). A 16-channel NORAXON electromyography system (Noraxon, Arizona, USA) was used to record synchronized muscle activation data of the VMO and VL, with technical specifications including a common-mode rejection ratio greater than 100 dB, amplifier gain of 1000, and an input impedance exceeding 10 MΩ. The EMG system had a channel bandwidth of 20–450 Hz, a sensitivity of 1 mV, and a sampling rate of 2000 Hz [ 31 ] . Finally, EMG data for each muscle were normalized to the maximum voluntary isometric contraction (MVIC) prior to the experimental task trials [ 17 ] . Data processing Analyses were performed using Visual 3D (C-Motion, Germantown, MD, USA). Ground reaction force and 3D kinematic data were filtered using a fourth-order, zero-lag Butterworth low-pass filter at cutoff frequencies of 50 Hz and 12 Hz, respectively. EMG signals were processed using a 20–450 Hz band-pass filter [ 32 ] and subjected to full-wave rectification to reduce motion artifacts caused by skin movement during exercise. The EMG activation ratio was used to quantify neuromuscular imbalance between the VMO and VL muscles, based on the ratio of their mean root-mean-square (RMS) amplitudes. Three-dimensional knee joint kinematics were calculated using tan X-Y-Z Cardan rotation sequence, with X corresponding to the sagittal plane, Y to the coronal plane, and Z to the transverse plane. The kinematic curves were normalized to 100% of the stance phase and then averaged across processed trials. Joint kinetics were calculated using Newton-Euler inverse dynamics [ 33 ] , and PFJ was estimated based on previous published methods [ 34 ] . Statistical analysis Descriptive statistics were used to report baseline demographics and characteristics for each treatment group. The Shapiro-Wilk test was applied to assess the normality of all outcome variables; if the assumption of normality was satisfied, descriptive analyses were conducted using means and standard deviations (M ± SD) for all dependent variables. A one-way ANOVA was conducted to compare age, height, and body mass among the three groups, while a chi-square test was used to examine group differences in sex and side of injury (healthy vs. affected). A 2 × 3 mixed-design ANOVA was conducted to evaluate the effects of intervention type and group on each outcome variable. If significant interactions were detected, post-hoc tests with the Bonferroni adjustments were performed. Partial eta squared (η 2 p ) was used to represent the magnitude of main and interaction effects in the two-factor repeated ANOVA. The criteria for effect size interpretation were as follows [ 35 ] : η 2 p < 0.01 indicated a very small effect; 0.01 ≤ η 2 p < 0.06 indicated a small effect; 0.06 ≤ η 2 p < 0.14 indicated a moderate effect; and η 2 p ≥ 0.14 indicated a large effect. Cohen's d was used to quantify the effect size in post-hoc comparisons to assess the intervention effect, and thresholds defined as follows [ 36 ] : d 0.80, large effect. The significance level α was set to 0.05, and data analyses were performed using SPSS software (Version 27.0, IBM, USA). Result Baseline characteristics Table 1 Baseline characteristics (M ± SD) EMS MST HE P value n = 20 n = 20 n = 18 Age(year) 22.5 ± 3.3 21.7 ± 2.0 21.44 ± 2.3 0.373 Height (m) 1.74 ± 0.07 1.75 ± 0.08 1.78 ± 0.07 0.138 Weight (kg) 73.0 ± 13.1 69.5 ± 11.7 72.0 ± 12.2 0.647 Body mass index (kg/m 2 ) 23.99 ± 2.94 22.65 ± 2.63 22.49 ± 2.81 0.164 Sex Male/ Female 18/15 13/7 16/2 0.214 Involved limb Left/ Right 9/14 8/12 9/9 0.751 Note: EMS: Neuromuscular electrical stimulation combined with muscle strength training; MST: Muscle strength training; HE: Health education; BMI: Body mass index. All dependent variables were normally distributed, as confirmed by the Shapiro–Wilk tests. One-way ANOVA tests showed no significant differences in age (P = 0.373), height (P = 0.138), weight (P = 0.647) and body mass index (P = 0.164) among the three groups. Chi-square tests showed no significant differences in sex (P = 0.214) or the involvement limbs (P = 0.751) among the three groups (Table 1 ). Pain and knee function A significant time*group interaction was detected in the VAS (P < 0.001, η 2 p = 0.232). Post hoc comparisons showed that the pain score was significantly decreased in both the EMS group (P < 0.001, Cohen's d = 3.18) and the MST group (P < 0.001, Cohen's d = 2.42) at week 7 compared with that at week 0. The pain score was lower in the EMS group (P < 0.001, Cohen's d = 1.76) compared with those in the HE group. Additionally, the pain score was lower in the MST group (P < 0.001, Cohen's d = 1.72) compared with those in the HE group (Fig. 3). A significant time*group interaction was detected in the AKPS (P < 0.001, η 2 p = 0.432). Post hoc comparisons showed that the AKPS score was significantly increased in both the EMS group (P < 0.001, Cohen's d = 1.24) and the MST group (P < 0.001, Cohen's d = 0.88) at week 7 compared with that at week 0. The AKPS score was greater in the EMS group compared with those in the MST and HE groups (P = 0.006, Cohen's d = 1.44; P<0.001, Cohen's d = 1.40) at week 7 (Fig. 3). Quadriceps strength Table 2 Comparison of quadriceps strength before and after intervention between three groups (M ± SD) EMS MST HE Time*group n = 20 n = 20 n = 18 P η 2 p Peak relative torque of knee extension (N*m/kg) Week 0 1.88 ± 0.58 2.06 ± 0.68 1.99 ± 0.45 0.001 0.222 Week 7 2.42 ± 0.60 a* 2.59 ± 0.73 a* 1.89 ± 0.35 Note: a Denotes significant difference compared with the HE group at week 7; b Denotes significant difference compared with the MST group at week 7; * Denotes significant difference between week 0 and 7. A significant time*group interaction was detected in the quadriceps strength (P < 0.001, η 2 p = 0.222). Post hoc comparisons showed that the quadriceps strength was significantly increased in both the EMS group (P < 0.001, Cohen's d = 0.93) and the MST group (P < 0.001, Cohen's d = 0.78) at week 7 compared with that at week 0. The quadriceps strength was greater in the EMS group (P = 0.023, Cohen's d = 1.51) compared with those in the HE group. Additionally, the quadriceps strength was greater in the MST group (P = 0.002, Cohen's d = 2.00) compared with those in the HE group (Table 2 ). Biomechanical characteristics of the patellofemoral joint Table 3 Biomechanical characteristics of the patellofemoral joint during stance phase of running(M ± SD) EMS MST HE Time*group n = 20 n = 20 n = 18 P η 2 p PFJ Stress, (Mpa) Week 0 5.93 ± 1.39 5.59 ± 1.61 5.67 ± 1.30 <0.001 0.390 Week 7 4.19 ± 0.99 a* 4.37 ± 1.39 a* 5.80 ± 1.22 PFJ Contact Area, (mm 2 ) Week 0 233.29 ± 12.53 236.22 ± 7.64 235.45 ± 5.42 0.571 0.019 Week 7 234.12 ± 9.99 234.55 ± 8.74 232.78 ± 11.04 PFJ Reaction Force, (N/kg) Week 0 19.06 ± 3.53 18.52 ± 3.71 19.15 ± 5.28 <0.001 0.347 Week 7 13.62 ± 3.07 a* 14.85 ± 4.47 a* 19.60 ± 4.83 Note: a Denotes significant difference compared with the HE group at week 7; b Denotes significant difference compared with the MST group at week 7; * Denotes significant difference between week 0 and 7. A significant time*group interaction was detected in the peak patellofemoral joint stress (P < 0.001, η 2 p = 0.390). Post hoc comparisons showed that the PFJ stress was significantly decreased in both the EMS group (P < 0.001, Cohen's d = 1.25) and the MST group (P < 0.001, Cohen's d = 0.76) at week 7 compared with that at week 0. The PFJ stress was lower in the EMS group (P < 0.001, Cohen's d = 1.37) compared with those in the HE group. Additionally, the PFJ stress was lower in the MST group (P = 0.001, Cohen's d = 1.17) compared with those in the HE group (Table 3 ). A significant time*group interaction was detected in the peak patellofemoral reaction force (P < 0.001, η 2 p = 0.347). Post hoc comparisons showed that the PFJ reaction force was significantly decreased in both the EMS group (P < 0.001, Cohen's d = 1.54) and the MST group (P < 0.001, Cohen's d = 0.99) at week 7 compared with that at week 0. The PFJ reaction force was lower in the EMS group (P < 0.001, Cohen's d = 1.24) compared with those in the HE group. Additionally, the pain score was lower in the MST group (P = 0.002, Cohen's d = 0.98) compared with those in the HE group (Table 3 ) No significant interaction was detected in the patellofemoral contact area, nor were there significant differences between or within groups at week 7 (Table 3 ). EMG of vastus medialis oblique and vastus lateralis Table 4 EMG of vastus medialis and vastus lateralis muscle during stance phase of running (M ± SD) EMS MST HE Time*group n = 20 n = 20 n = 18 P η 2 p VMO Amplitude Week 0 0.76 ± 0.28 0.81 ± 0.25 0.80 ± 0.30 <0.001 0.338 Week 7 1.09 ± 0.27 ab* 0.91 ± 0.30 * 0.71 ± 0.21 VL Amplitude Week 0 1.04 ± 0.29 0.97 ± 0.26 0.91 ± 0.33 <0.001 0.107 Week 7 1.06 ± 0.32 1.11 ± 0.29 * 0.93 ± 0.29 VMO: VL Amplitude Ratio Week 0 0.74 ± 0.24 0.88 ± 0.34 0.96 ± 0.44 <0.001 0.351 Week 7 1.07 ± 0.31 ab * 0.84 ± 0.28 0.83 ± 0.33b * Note: a Denotes significant difference compared with the HE group at week 7; b Denotes significant difference compared with the MST group at week 7; * Denotes significant difference between week 0 and 7. A significant time*group interaction was detected in the VMO Amplitude (P < 0.001, η 2 p = 0.338). Post hoc comparisons showed that the VMO Amplitude was significantly increased in both the EMS group (P < 0.001, Cohen's d = 1.18) and the MST group (P = 0.039, Cohen's d = 0.40) at week 7 compared with that at week 0. The VMO Amplitude was greater in the EMS group compared with those in the MST and HE groups (P = 0.035, Cohen's d = 0.67; P<0.001, Cohen's d = 1.41) at week 7 (Table 4 ). A significant time*group interaction was detected in the VL Amplitude (P < 0.001, η 2 p = 0.107). Post hoc comparisons showed that the VL Amplitude was significantly increased in both the MST group (P = 0.001, Cohen's d = 0.54) at week 7 compared with that at week 0 (Table 4 ). A significant time*group interaction was detected in the VMO: VL amplitude ratio (P < 0.001, η 2 p = 0.351). Post hoc comparisons showed that the VMO: VL amplitude ratio was significantly increased in both the EMS group (P < 0.001, Cohen's d = 1.37) and the HE group (P = 0.018, Cohen's d = 0.30) at week 7 compared with that at week 0. The VMO: VL amplitude ratio was greater in the EMS group compared with those in the MST and HE groups (P = 0.035, Cohen's d = 0.74; P = 0.042, Cohen's d = 0.73) at week 7 (Table 4 ). Discussion This study investigated the effects of a 6-week intervention involving EMS, MST, and HE on pain, knee function, muscle strength, muscle activations of VMO and VL and PFPS during running among people with PFP. The findings support the first hypothesis and partially support the second hypothesis. The results demonstrated that both EMS and MST were effective in relieving pain, improving knee function compared to HE among people with PFP. In addition, EMS demonstrating superior improvements in knee function compared with MST. These findings are consistent with previous studies. Bily et al. [ 37 ] reported enhanced pain relief and functional recovery with the combination of exercise and electrical stimulation, while Paillard [ 38 ] highlighted the benefits of combining electrical stimulation with voluntary contractions compared to exercise alone. Glaviano and Saliba [ 20 ] further supported these findings, noting that NMES combined with exercise alleviates pain, reduces muscle fatigue, and enhances neuromuscular adaptations, thereby improving muscle strength and compensation movement strategies. The observed benefits may be attributed to several mechanisms. Strengthening hip and knee musculature improves pelvic control, balances joint loading, and enhances lower limb stability [ 39 ] . These adaptations reduce joint stress and friction and promote blood flow and tissue nutrition. Post-training stretching and relaxation further optimize soft tissue flexibility [ 40 ] , thereby reducing abnormal tension and minimizing cartilage degeneration. NMES likely contributes to pain modulation through mechanisms such as the gate control theory [ 41 ] and endorphin opioid release [ 42 ] . Additionally, NMES enhances microvascular perfusion and decreases capillary permeability [ 43 , 44 ] , facilitating circulation and reducing edema. Collectively, these effects create a favorable biomechanical and physiological environment for joint recovery, which may account for the greater reductions in pain and enhancements in function observed in the EMS group. Regarding muscle activation, both EMS and MST interventions improved knee extensor strength and VMO activation, with the EMS more effectively correcting imbalances between VMO and VL. Steadman [ 45 ] proposed that NMES enhances VMO motor unit recruitment, thereby restoring quadriceps force balance and improving patellar tracking. This aligns with evidence that the mechanism of action potentials involved in NMES is similar to that of voluntary muscle contraction. The current generated by neuromuscular electrical stimulation stimulates motor nerve axons and/or intramuscular nerve endings leading to changes in muscle membrane potential. This subsequently triggers calcium release, activates the signaling cascade, and ultimately induces skeletal muscle contraction [ 45 ] . Such rhythmic muscle contractions can increase motor unit recruitment and maintain sustained high-intensity firing rates, thereby generating greater force output and accelerate nerve regeneration [ 46 , 47 ] . The integration of NMES with voluntary contractions may further enhance spinal excitability and Ia reflex plasticity [ 48 ] , facilitating broader motor unit activation and greater force output. These mechanisms likely underpin the combined intervention’s superior efficacy in correcting muscle imbalances, which is essential for minimizing patellofemoral instability during weight-bearing activities. Although both interventions reduced patellofemoral joint stress and increased quadriceps strength, no statistically significant differences were observed between the EMS and MST groups. Labanca et al. [ 49 ] reported similar strength gains following eight weeks of NMES combined with resistance training compared to conventional training in patients with patellar tendinopathy. A meta-analysis by Hopp and WK. [ 50 ] also found comparable improvements knee extension strength between NMES and traditional resistance training, suggesting a potential ceiling effect at approximately 70% one-repetition maximum (1RM) intensity [ 37 , 51 ] . Nevertheless, Martimbianco et al. [ 18 ] noted that combined training protocols specifically enhance VMO strength and correct medial-lateral imbalances, potentially reducing knee valgus and injury risk. The absence of intergroup differences in the present study may be attributable to suboptimal NMES dosage, an insufficient number of repetitions [ 47 ] , or sex-related kinematic variations that may have influenced statistical power [ 52 ] . Several limitations should be acknowledged. Heterogeneity in age, sex, injury severity, and etiology may influence the outcomes [ 52 ] , and participant attrition limited the feasibility of subgroup analyses. Long-term follow-up was not conducted, precluding evaluation of sustained efficacy. Future studies should incorporate stratified analyses based on demographic and injury-related factors, extend the duration of interventions, and include post-rehabilitation monitoring to assess long-term effects. Despite these constraints, the findings underscore the clinical value of combining NMES with strength training for PFP management, particularly in optimizing functional recovery and addressing neuromuscular imbalances. Further research aimed at refining stimulation parameters and exploring individualized intervention protocols will enhance the development of evidence-based rehabilitation strategies. Conclusion This study confirmed that a 6-week electrical stimulation combined with muscle strength training regime positively affected the symptoms by relieving pain, improving knee function, and balancing muscle activation of VMO and VL among individuals with PFP. Those observations support that EMS should be recommended as one of the clinical treatments for people with PFP. Abbreviations PFP Patellofemoral pain PFJS Patellofemoral joint stress VMO Vastus medialis oblique VL vastus lateralis NMES Neuromuscular electrical stimulation MST Muscle strength training HE health education AKPS Anterior Knee Pain Scale 1RM 1 repetition maximum VAS Visual analog scale EMG Electromyography Declarations This study adheres to the CONSORT guidelines. Ethics approval and consent to participate The study followed the institutional requirements and was approved by the Shandong Sport University Committee for Human Investigations (2022012), Prior to the study, the participants provided a written informed consent to participate. Consent for publication All participants in this study provided written informed consent for the publication of their personal and clinical details, as well as any identifiable images included in this study. All participants approved the submitted version of the manuscript for publication. Conflict of interest The authors declare that they have no conflicts of interest relevant to the content of this article. Funding This work was supported by Tai 'an Central Hospital funded by the Shandong Provincial Traditional Chinese Medicine Science and Technology Project [M-2022080]. Author Contribution All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by J.W. and YC.Y. The first draft of the manuscript was written by J.W. and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Acknowledgement We express our gratitude to the Laboratory of Sports Biomechanics at Shandong Sport University for the technical support provided during data collection in this study; we also sincerely thank all participants for their full commitment to this research. 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15:35:14","extension":"html","order_by":37,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":159462,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7611495/v1/1602c3313205293e036fdac8.html"},{"id":93248350,"identity":"0c85ae8f-55cc-4add-b937-5342da613d6f","added_by":"auto","created_at":"2025-10-10 15:35:13","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":36151,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eParticipation flow chart. \u003c/strong\u003eFinal analysis included data from 58 participants. 14 participants were excluded from the original 72 recruited due to various reasons; EMS: Neuromuscular electrical stimulation combined with muscle strength training; MST: Muscle strength training; HE: Health education.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7611495/v1/4368ca98b06a770b693a6fc9.png"},{"id":93250321,"identity":"f93017c0-eb6f-4f19-b075-1a3a684015ba","added_by":"auto","created_at":"2025-10-10 15:43:13","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":274762,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eIllustrations of the muscle strength training movements.\u003c/strong\u003e (A) self-weight squat, (B) barbell squats, (C) knee extension against resistance, (D) static hip bridge, (E) barbell hip push, (F) clamshell exercise.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7611495/v1/851874fc79508c082be4c490.png"},{"id":93248345,"identity":"ccff4f3c-5cae-4a12-9032-ba8b9f1667b8","added_by":"auto","created_at":"2025-10-10 15:35:13","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":51250,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of pain and knee function before and after intervention between three groups\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNote: \u003csup\u003ea \u003c/sup\u003eDenotes significant difference compared with the HE group at week 7; \u003csup\u003eb \u003c/sup\u003eDenotes significant difference compared with the MST group at week 7; \u003csup\u003e* \u003c/sup\u003eDenotes significant difference between week 0 and 7.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7611495/v1/4ae7b42da021cea0de6b722c.png"},{"id":93375528,"identity":"4439d0e4-655c-4393-af1a-b1b88b061f19","added_by":"auto","created_at":"2025-10-13 08:09:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1502473,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7611495/v1/094b2d83-cdd4-4af2-845c-4143ffcf3c90.pdf"},{"id":93250326,"identity":"6cda7d64-216c-4f87-bfaa-56e19abddb74","added_by":"auto","created_at":"2025-10-10 15:43:13","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":247954,"visible":true,"origin":"","legend":"","description":"","filename":"CONSORT2025editablechecklist9.23.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7611495/v1/85f30858dbe3633f7f56eb81.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effects of muscle strength training combined with neuromuscular electrical stimulation on pain, function, muscle strength, patellar stress, and muscle activation during running in people with patellofemoral pain","fulltext":[{"header":"Background","content":"\u003cp\u003ePatellofemoral pain (PFP) is a prevalent musculoskeletal condition among young individuals, characterized by insidious pain not attributable to trauma or identifiable pathology \u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e. The hallmark of PFP is intermittent pain, provoked by activities that elevate stress on the patellofemoral joint, such as prolonged sitting with flexed knees, running, stair climbing, and squatting \u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. Although PFP is often regarded as a self-limiting condition, evidence suggests that its symptoms frequently persist for years \u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e. This chronic pain not only adversely affects an individual's physical activity levels and quality of life, but also heightens the risk of developing knee osteoarthritis over time \u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eElevated patellofemoral joint stress (PFJS) represents a primary pathological mechanism underlying PFP \u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e. Abnormal patellar tracking leads to stress concentration on subchondral bone, accelerating cartilage degeneration and resulting in pain \u003csup\u003e[\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. Quadriceps muscle imbalance and hip muscle weakness are key biomechanical contributors to increased PFJS \u003csup\u003e[\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e. Specifically, imbalances and abnormal activation between the vastus medialis oblique (VMO) and vastus lateralis (VL) disrupt patellar stability, causing abnormal lateral tension, and altering patellar tracking and joint loading distribution. Weakness in the hip abductor and external rotator muscles impair femoral control, leading to increased dynamic knee valgus during functional activities and a significantly rise in PFJS \u003csup\u003e[\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e. Consequently, strengthening both hip and knee muscles, particularly by improving quadriceps balance and hip muscle control, which is crucial intervention for reducing PFJS and lowering the risk of injury.\u003c/p\u003e\u003cp\u003eStrength training is a critical component of the PFP rehabilitation programs, designed to alleviate pain and enhance function, typically targeting on strengthening the quadriceps and gluteal muscles. Research indicates \u003csup\u003e[\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e that strengthening hip and knee muscles not only alleviates pain but also enhances physical function, including improved posture control, increased pelvic stability, and reducing joint loading during running. However, conventional strength training approaches require refinement to effectively address strength imbalances in VMO and VL, which may contribute to abnormal patellar tracking during movement and symptom recurrence \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e. Consequently, current rehabilitation programs require further optimization to more effectively mitigate this issue.\u003c/p\u003e\u003cp\u003eNeuromuscular electrical stimulation (NMES) is an established adjunctive therapeutic approach for the neuromuscular rehabilitation of atrophied or weakened muscles \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. NMES not only alleviates pain but also enhances the function of targeted muscles, activates muscle fibers challenging to engage through conventional training, and promotes to comprehensive muscle strength improvement \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. Conventional quadriceps strengthening exercises may not effectively activate the vastus medialis muscle, resulting in challenges in correcting the strength imbalance between the VMO and VL \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e. Therefore, integrating NMES to activate the VMO during strength training may facilitate improved balance of strength between the VMO and VL, optimizing the patellofemoral joint trajectory during movement, reducing joint stress, and ultimately achieving pain and enhancing lower limb function.\u003c/p\u003e\u003cp\u003eThis study aims to investigate the effects of a 6-week intervention involving NMES combined with strength training (EMS) on pain, function, muscle strength, patellar stress, and muscle activation during running in people with PFP. The study hypothesizes that: (1) Both the EMS group and the muscle strength training (MST) group will effectively alleviate pain, enhance functional outcomes, increase knee extensor strength, and reduce PFJS during running. (2) Compared with the MST group and the health education (HE) group, the EMS group will demonstrate greater improvements in alleviating pain, reducing PFJS during running, increasing activation of the VMO, and enhancing functional outcomes and knee extensor strength.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eSample-size calculating\u003c/h2\u003e\u003cp\u003eSample size was determined through power analysis using the G*Power software (Version 3.1.9.6, Franz Faul, University of Kiel, Germany), based on previous research \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e involving a six-week standardized muscle strength training combined with neuromuscular electrical stimulation therapy for 27 PFP patients. By comparing the Anterior Knee Pain Scale (AKPS) scores of PFP patients in the experimental group before and after the intervention (increased from 60.4 ± 14.8 to 73.0 ± 14.3), with a significance level of α = 0.05, Type II error β = 0.20, and power (1-β) = 0.80, the minimum sample size was calculated as n = 13. Considering a potential dropout rate of 20%, each group in this study was determined to require at least 16 subjects.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eParticipant recruitment\u003c/h3\u003e\n\u003cp\u003eAll participants were between the ages of 18 and 35 years. Participants with PFP recruited for this study met the following criteria \u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e:(1) prepatellar or retropatellar knee pain following at least two of the following activities— prolonged sitting, stair climbing, squatting, running, kneeling, jumping, and deep knee flexion with resisted knee extension; (2) insidious onset of symptoms unrelated to trauma; and (3) pain persisting for a minimum of three months. Exclusion criteria \u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e included: (1) other knee disorders, including meniscal or other intra-articular injuries, a history of recurrent patellar subluxation or dislocation, or prior knee surgery; and (2) contraindications to low-frequency electrotherapy or inability to tolerate electrical stimulation.\u003c/p\u003e\u003cp\u003eAfter receiving trial information from a physical therapist and being given at least 24 hours to consider participation, the investigator obtained written informed consent and scheduled trial visits. The knee with the most severe symptoms at baseline was designated as the study knee.\u003c/p\u003e\u003cp\u003eAll participants were recruited through posted flyers in the Shandong Sport University, athletic health clubs, and local sports training center. All potential participants were screened by a licensed physical therapist to assess eligibility based on the inclusion and exclusion criteria. Those who met the criteria were consecutively enrolled and reported to the Biomechanics Laboratory at Shandong Sport University for testing. Participants provided written informed consent, and the study was approved by the Shandong Sport University Committee for Human Investigations (2022012), registered with the Chinese Clinical Trial Registry (registration number: ChiCTR2300067598). and conducted in accordance with the Declaration of Helsinki.\u003c/p\u003e\n\u003ch3\u003eRandomization and allocation\u003c/h3\u003e\n\u003cp\u003eThe study included 72 eligible participants enrolled in the trial. To achieve concealed allocation and simple randomization, a researcher not involved in patient recruitment or treatment employed the RAND function in Microsoft Excel to generate random numbers prior to data collection. Based on these numbers, the 72 participants who met the trial criteria were matched according to general characteristics such as age, height, weight, and gender, and then allocated to one of three groups: the electrical stimulation combined with muscle strength training group (EMS), the muscle strength training group (MST), and the health education group (HE), with 24 participants in each group. At week 0 (within one week prior to the intervention) and week 7 (within one week after the intervention), the affected lower extremity of each participant was assessed using standardized measures. In cases where both knees were symptomatic, the more severely affected side was selected for evaluation. During the 6-week intervention, attendance was monitored by designated personnel. To maintain scientific rigor, participants with attendance rates below 85%, those who received additional treatments during the intervention period, or those who experienced accidental injuries outside of the intervention were excluded. Ultimately, 58 participants completed the study: 20 in each of the EMS and MST groups, and 18 in the HE Group (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\n\u003ch3\u003eInterventions\u003c/h3\u003e\n\u003cp\u003eThe treatment regimen for both the MST and EMS groups consisted of 18 sessions over a 6-week period (3 sessions per week), each supervised by an experienced clinical physiotherapist. The primary aim was to avoid pain during all exercises and to prevent abnormal movement patterns or engagement in additional unsanctioned physical activities. The physiotherapist assisted each participant during the sessions, supervising and correcting t posture before and during the execution of each exercise, and providing corrective feedback as needed. Following the recommendations of the American College of Sports Medicine (ACSM) \u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e, each session followed predetermined phases: a warm-up, a main training component, and a concluding cool-down with stretching. The warm-up phase comprised dynamic lower extremity exercises designed to increase blood flow, raise muscle temperature, and activate the central nervous system.\u003c/p\u003e\u003cp\u003ePlyometric training included bodyweight or resistance-based strength exercises targeting the quadriceps, gluteus maximus, and gluteus medius muscles. Each session incorporated 4–5 selected movements (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), lasting 40 to 60 minutes. Perform each movement three times with 60-second rests between sets. Training was performed three times a week, following progressive overload principles and including individualized adjustments to training load intensity. Load was standardized at 70% of each individual’s estimated 1-repetition maximum (1RM) capacity \u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e. Each session concluded with full-body stretching and lower extremity relaxation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eParticipants in the EMS group performed the same supervised exercise program as those in the MST group. In addition, reusable, self-adhesive electrode pads were placed on the VMO of the affected leg prior to plyometric training, and electrical stimulation was superimposed on knee extensor muscles contractions to facilitate activation and strengthen the VMO. The electrodes were positioned along the muscle fibers, with the cathode placed 4 cm above and 3 cm medial to the patella, and the anode positioned 10 cm above the patella and medial to the mid-thigh line. Using a Digitimer DS7AH (Digitimer Ltd ., Welwyn Garden City, UK), participants received individually adjusted maximum permissible intensities \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. The NMES parameters were set as follows: a square waveform with a pulse width of 400 µs, frequency of 50 Hz, pulse duration of 250 µs, and a work-rest cycle of 10–50 seconds. The stimulation current was maintained below 100 mA \u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. To accommodate the progressive increase in participant tolerance, stimulation intensity was adjusted every two weeks to optimize motor unit recruitment \u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e. 9/19/2025\u003c/p\u003e\u003cp\u003eParticipants in the HE group did not receive any exercise intervention but attended weekly educational sessions focused on strategies to protect the knee from injury during running and daily activities. Additionally, educational articles about PFP management were distributed online. The health education program also lasted 6 weeks. Participants were instructed not to engage in any exercise program or therapeutic intervention during this period, and exercise training could be initiated after the 6-week control phase.\u003c/p\u003e\n\u003ch3\u003eOutcome measures\u003c/h3\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003ePain\u003c/h2\u003e\u003cp\u003ePain score was measured using a visual analog scale (VAS), which quantifies the highest level of pain experienced during activity in the previous week. During the assessment, participants marked their perceived pain level on a 10 cm VAS, where 0 indicated “no pain” and 10 represented “worst imaginable pain”. The distance from the left anchor point to the participant's mark was recorded as the pain score \u003csup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eFunction\u003c/h3\u003e\n\u003cp\u003eSelf-reported knee function was assessed using the Anterior Knee Pain Scale (AKPS) \u003csup\u003e[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e, a 13-item questionnaire addressing symptoms and functional limitations such as stair climbing, walking, running, jumping, and prolonged sitting. The AKPS score ranges from 0 to 100, with lower scores representing greater functional impairment.\u003c/p\u003e\n\u003ch3\u003eMuscle strength\u003c/h3\u003e\n\u003cp\u003eIsokinetic muscle strength of the affected limb was assessed using the IsoMed 2000 isokinetic dynamometer (D\u0026amp;R Ferstl GmbH, Hemau, Germany). Participants were seated in a stable position with immobilization straps to prevent compensatory trunk movements. The axis of rotation of the device was aligned with the knee joint and gravity compensation was applied. Prior to testing, participants performed five practice contractions to become familiar with the procedure and to ensure proper strap placement on the torso, lower back, and thighs, minimizing compensatory movements at adjacent joints. After a 5-minute rest, isokinetic torque of the quadriceps was measured at an angular velocity of 60°/s during continuous, bidirectional knee flexion-extension movements \u003csup\u003e[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003c/sup\u003e. Participants exerted maximal force as rapidly as possible to familiarize themselves with the task and ensure consistent force production during the formal trials. Each participant completed the test a minimum of three times.\u003c/p\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eBiomechanical data collection\u003c/h2\u003e\u003cp\u003eParticipants were instructed to wear standardized tights and running shoes, complete a 10-minutes warm-up, and familiarize themselves with the test procedures. Following the warm-up, 41 reflective markers were affixed to the participant’s body based on surface anatomical landmarkers. Electrode placement sites for the VMO and VL muscles on the affected lower limb were also determined. Prior to electrode application, the skin at each placement site was shaved, cleansed with alcohol, lightly abraded, and cleaned using a medical abrasive paste to reduce impedance. Bipolar Ag-AgCl surface electrodes with a 10-mm interelectrode distance were applied to the target muscles to record muscle activity. Electrode placement followed the guidelines of the Surface Electromyography for the Non-Invasive Assessment of Muscles (SENIAM) \u003csup\u003e[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eParticipants then stood in the anatomical position to undergo a 5-second static calibration. After calibration, they moved to the starting point of a simulated running track, located 8 meters from the force platform. Participants ran at a self-selected speed using a heel-to-toe running pattern and completed a foot strike with the affected leg on the force platform. Each participant completed three successful trials, with 1–2 minutes of rest between each. The entire running process was performed without any pace adjustment, with movement being natural and continuous.\u003c/p\u003e\u003cp\u003eData collection was conducted using a 12-camera Vicon motion capture system (Nexus 12.0, Vicon Motion Systems, Oxford, UK) at a sampling frequency of 100 Hz to capture 3D marker trajectories. Ground reaction forces were collected at 1000 Hz using an AMTI force platform (AMTI, Inc., Watertown, MA, USA). A 16-channel NORAXON electromyography system (Noraxon, Arizona, USA) was used to record synchronized muscle activation data of the VMO and VL, with technical specifications including a common-mode rejection ratio greater than 100 dB, amplifier gain of 1000, and an input impedance exceeding 10 MΩ. The EMG system had a channel bandwidth of 20–450 Hz, a sensitivity of 1 mV, and a sampling rate of 2000 Hz \u003csup\u003e[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u003c/sup\u003e. Finally, EMG data for each muscle were normalized to the maximum voluntary isometric contraction (MVIC) prior to the experimental task trials \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eData processing\u003c/h2\u003e\u003cp\u003eAnalyses were performed using Visual 3D (C-Motion, Germantown, MD, USA). Ground reaction force and 3D kinematic data were filtered using a fourth-order, zero-lag Butterworth low-pass filter at cutoff frequencies of 50 Hz and 12 Hz, respectively. EMG signals were processed using a 20–450 Hz band-pass filter \u003csup\u003e[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e and subjected to full-wave rectification to reduce motion artifacts caused by skin movement during exercise. The EMG activation ratio was used to quantify neuromuscular imbalance between the VMO and VL muscles, based on the ratio of their mean root-mean-square (RMS) amplitudes.\u003c/p\u003e\u003cp\u003eThree-dimensional knee joint kinematics were calculated using tan X-Y-Z Cardan rotation sequence, with X corresponding to the sagittal plane, Y to the coronal plane, and Z to the transverse plane. The kinematic curves were normalized to 100% of the stance phase and then averaged across processed trials. Joint kinetics were calculated using Newton-Euler inverse dynamics \u003csup\u003e[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/sup\u003e, and PFJ was estimated based on previous published methods \u003csup\u003e[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eStatistical analysis\u003c/h2\u003e\u003cp\u003eDescriptive statistics were used to report baseline demographics and characteristics for each treatment group. The Shapiro-Wilk test was applied to assess the normality of all outcome variables; if the assumption of normality was satisfied, descriptive analyses were conducted using means and standard deviations (M ± SD) for all dependent variables. A one-way ANOVA was conducted to compare age, height, and body mass among the three groups, while a chi-square test was used to examine group differences in sex and side of injury (healthy vs. affected). A 2 × 3 mixed-design ANOVA was conducted to evaluate the effects of intervention type and group on each outcome variable. If significant interactions were detected, post-hoc tests with the Bonferroni adjustments were performed. Partial eta squared (η\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e) was used to represent the magnitude of main and interaction effects in the two-factor repeated ANOVA. The criteria for effect size interpretation were as follows\u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e: η\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e \u0026lt; 0.01 indicated a very small effect; 0.01 ≤ η\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e \u0026lt; 0.06 indicated a small effect; 0.06 ≤ η\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e \u0026lt; 0.14 indicated a moderate effect; and η\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e ≥ 0.14 indicated a large effect. Cohen's \u003cem\u003ed\u003c/em\u003e was used to quantify the effect size in post-hoc comparisons to assess the intervention effect, and thresholds defined as follows \u003csup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/sup\u003e : \u003cem\u003ed\u003c/em\u003e \u0026lt; 0.20, negligible effect; 0.20 ≤ \u003cem\u003ed\u003c/em\u003e ≤ 0.50, small effect; 0.51 ≤ \u003cem\u003ed\u003c/em\u003e ≤ 0.80, medium effect; and \u003cem\u003ed\u003c/em\u003e \u0026gt; 0.80, large effect. The significance level α was set to 0.05, and data analyses were performed using SPSS software (Version 27.0, IBM, USA).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"Result","content":"\u003ch2\u003eBaseline characteristics\u003c/h2\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eBaseline characteristics (M\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\u003ccolgroup\u003e\u003c/colgroup\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eEMS\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMST\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eHE\u003c/p\u003e\n\u003c/th\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eP value\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003en\u0026thinsp;=\u0026thinsp;20\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003en\u0026thinsp;=\u0026thinsp;20\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003en\u0026thinsp;=\u0026thinsp;18\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\u003e\u003cstrong\u003eAge(year)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e21.7\u0026thinsp;\u0026plusmn;\u0026thinsp;2.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e21.44\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.373\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eHeight (m)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.78\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.138\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eWeight (kg)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e73.0\u0026thinsp;\u0026plusmn;\u0026thinsp;13.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e69.5\u0026thinsp;\u0026plusmn;\u0026thinsp;11.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e72.0\u0026thinsp;\u0026plusmn;\u0026thinsp;12.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.647\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eBody mass index (kg/m\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e23.99\u0026thinsp;\u0026plusmn;\u0026thinsp;2.94\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22.65\u0026thinsp;\u0026plusmn;\u0026thinsp;2.63\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22.49\u0026thinsp;\u0026plusmn;\u0026thinsp;2.81\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.164\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eSex\u003c/strong\u003e\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\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eMale/ Female\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e18/15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e13/7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e16/2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.214\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eInvolved limb\u003c/strong\u003e\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\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eLeft/ Right\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9/14\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8/12\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9/9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.751\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003ctfoot\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"5\"\u003eNote: EMS: Neuromuscular electrical stimulation combined with muscle strength training; MST: Muscle strength training; HE: Health education; BMI: Body mass index.\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tfoot\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll dependent variables were normally distributed, as confirmed by the Shapiro\u0026ndash;Wilk tests. One-way ANOVA tests showed no significant differences in age (P\u0026thinsp;=\u0026thinsp;0.373), height (P\u0026thinsp;=\u0026thinsp;0.138), weight (P\u0026thinsp;=\u0026thinsp;0.647) and body mass index (P\u0026thinsp;=\u0026thinsp;0.164) among the three groups. Chi-square tests showed no significant differences in sex (P\u0026thinsp;=\u0026thinsp;0.214) or the involvement limbs (P\u0026thinsp;=\u0026thinsp;0.751) among the three groups (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003ch2\u003ePain and knee function\u003c/h2\u003e\n\u003cp\u003eA significant time*group interaction was detected in the VAS (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, \u0026eta;\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.232). Post hoc comparisons showed that the pain score was significantly decreased in both the EMS group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;3.18) and the MST group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.42) at week 7 compared with that at week 0. The pain score was lower in the EMS group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.76) compared with those in the HE group. Additionally, the pain score was lower in the MST group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.72) compared with those in the HE group (Fig.\u0026nbsp;3).\u003c/p\u003e\n\u003cp\u003eA significant time*group interaction was detected in the AKPS (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, \u0026eta;\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.432). Post hoc comparisons showed that the AKPS score was significantly increased in both the EMS group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.24) and the MST group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.88) at week 7 compared with that at week 0. The AKPS score was greater in the EMS group compared with those in the MST and HE groups (P\u0026thinsp;=\u0026thinsp;0.006, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.44; P\u0026lt;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.40) at week 7 (Fig.\u0026nbsp;3).\u003c/p\u003e\n\u003ch2\u003eQuadriceps strength\u003c/h2\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eComparison of quadriceps strength before and after intervention between three groups (M\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\u003ccolgroup\u003e\u003c/colgroup\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eEMS\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMST\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eHE\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eTime*group\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003en\u0026thinsp;=\u0026thinsp;20\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003en\u0026thinsp;=\u0026thinsp;20\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003en\u0026thinsp;=\u0026thinsp;18\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eP\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u0026eta;\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003ePeak relative torque of knee extension (N*m/kg)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.68\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e1.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.45\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.222\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.60 \u003csup\u003ea*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.59\u0026thinsp;\u0026plusmn;\u0026thinsp;0.73 \u003csup\u003ea*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e1.89\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35\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 Denotes significant difference compared with the HE group at week 7; \u003csup\u003eb\u003c/sup\u003e Denotes significant difference compared with the MST group at week 7; \u003csup\u003e*\u003c/sup\u003e Denotes significant difference between week 0 and 7.\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tfoot\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;A significant time*group interaction was detected in the quadriceps strength (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, \u0026eta;\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.222). Post hoc comparisons showed that the quadriceps strength was significantly increased in both the EMS group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.93) and the MST group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.78) at week 7 compared with that at week 0. The quadriceps strength was greater in the EMS group (P\u0026thinsp;=\u0026thinsp;0.023, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.51) compared with those in the HE group. Additionally, the quadriceps strength was greater in the MST group (P\u0026thinsp;=\u0026thinsp;0.002, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.00) compared with those in the HE group (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eBiomechanical characteristics of the patellofemoral joint\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab3\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eBiomechanical characteristics of the patellofemoral joint during stance phase of running(M\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\u003ccolgroup\u003e\u003c/colgroup\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eEMS\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMST\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eHE\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eTime*group\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003en\u0026thinsp;=\u0026thinsp;20\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003en\u0026thinsp;=\u0026thinsp;20\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003en\u0026thinsp;=\u0026thinsp;18\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eP\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u0026eta;\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003ePFJ Stress, (Mpa)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5.93\u0026thinsp;\u0026plusmn;\u0026thinsp;1.39\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5.59\u0026thinsp;\u0026plusmn;\u0026thinsp;1.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5.67\u0026thinsp;\u0026plusmn;\u0026thinsp;1.30\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.390\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.99 \u003csup\u003ea*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4.37\u0026thinsp;\u0026plusmn;\u0026thinsp;1.39 \u003csup\u003ea*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5.80\u0026thinsp;\u0026plusmn;\u0026thinsp;1.22\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003ePFJ Contact Area, (mm\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e233.29\u0026thinsp;\u0026plusmn;\u0026thinsp;12.53\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e236.22\u0026thinsp;\u0026plusmn;\u0026thinsp;7.64\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e235.45\u0026thinsp;\u0026plusmn;\u0026thinsp;5.42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.571\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.019\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e234.12\u0026thinsp;\u0026plusmn;\u0026thinsp;9.99\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e234.55\u0026thinsp;\u0026plusmn;\u0026thinsp;8.74\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e232.78\u0026thinsp;\u0026plusmn;\u0026thinsp;11.04\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003ePFJ Reaction Force, (N/kg)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e19.06\u0026thinsp;\u0026plusmn;\u0026thinsp;3.53\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e18.52\u0026thinsp;\u0026plusmn;\u0026thinsp;3.71\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e19.15\u0026thinsp;\u0026plusmn;\u0026thinsp;5.28\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.347\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e13.62\u0026thinsp;\u0026plusmn;\u0026thinsp;3.07 \u003csup\u003ea*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e14.85\u0026thinsp;\u0026plusmn;\u0026thinsp;4.47 \u003csup\u003ea*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e19.60\u0026thinsp;\u0026plusmn;\u0026thinsp;4.83\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 Denotes significant difference compared with the HE group at week 7; \u003csup\u003eb\u003c/sup\u003e Denotes significant difference compared with the MST group at week 7; \u003csup\u003e*\u003c/sup\u003e Denotes significant difference between week 0 and 7.\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tfoot\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;A significant time*group interaction was detected in the peak patellofemoral joint stress (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, \u0026eta;\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.390). Post hoc comparisons showed that the PFJ stress was significantly decreased in both the EMS group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.25) and the MST group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.76) at week 7 compared with that at week 0. The PFJ stress was lower in the EMS group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.37) compared with those in the HE group. Additionally, the PFJ stress was lower in the MST group (P\u0026thinsp;=\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.17) compared with those in the HE group (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eA significant time*group interaction was detected in the peak patellofemoral reaction force (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, \u0026eta;\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.347). Post hoc comparisons showed that the PFJ reaction force was significantly decreased in both the EMS group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.54) and the MST group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.99) at week 7 compared with that at week 0. The PFJ reaction force was lower in the EMS group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.24) compared with those in the HE group. Additionally, the pain score was lower in the MST group (P\u0026thinsp;=\u0026thinsp;0.002, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.98) compared with those in the HE group (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e)\u003c/p\u003e\n\u003cp\u003eNo significant interaction was detected in the patellofemoral contact area, nor were there significant differences between or within groups at week 7 (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n\u003ch2\u003eEMG of vastus medialis oblique and vastus lateralis\u003c/h2\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab4\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eEMG of vastus medialis and vastus lateralis muscle during stance phase of running (M\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\u003ccolgroup\u003e\u003c/colgroup\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eEMS\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMST\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eHE\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eTime*group\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003en\u0026thinsp;=\u0026thinsp;20\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003en\u0026thinsp;=\u0026thinsp;20\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003en\u0026thinsp;=\u0026thinsp;18\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eP\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u0026eta;\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eVMO Amplitude\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.81\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.80\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.338\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.09\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27 \u003csup\u003eab*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eVL Amplitude\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.04\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.26\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.33\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.107\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.93\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eVMO: VL Amplitude Ratio\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.34\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.96\u0026thinsp;\u0026plusmn;\u0026thinsp;0.44\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003e0.351\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeek\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.07\u0026thinsp;\u0026plusmn;\u0026thinsp;0.31 \u003csup\u003eab *\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.83\u0026thinsp;\u0026plusmn;\u0026thinsp;0.33b\u003csup\u003e*\u003c/sup\u003e\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 Denotes significant difference compared with the HE group at week 7; \u003csup\u003eb\u003c/sup\u003e Denotes significant difference compared with the MST group at week 7; \u003csup\u003e*\u003c/sup\u003e Denotes significant difference between week 0 and 7.\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tfoot\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;A significant time*group interaction was detected in the VMO Amplitude (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, \u0026eta;\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.338). Post hoc comparisons showed that the VMO Amplitude was significantly increased in both the EMS group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.18) and the MST group (P\u0026thinsp;=\u0026thinsp;0.039, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.40) at week 7 compared with that at week 0. The VMO Amplitude was greater in the EMS group compared with those in the MST and HE groups (P\u0026thinsp;=\u0026thinsp;0.035, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.67; P\u0026lt;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.41) at week 7 (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eA significant time*group interaction was detected in the VL Amplitude (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, \u0026eta;\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.107). Post hoc comparisons showed that the VL Amplitude was significantly increased in both the MST group (P\u0026thinsp;=\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.54) at week 7 compared with that at week 0 (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eA significant time*group interaction was detected in the VMO: VL amplitude ratio (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, \u0026eta;\u003csup\u003e2\u003c/sup\u003e\u003csub\u003ep\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.351). Post hoc comparisons showed that the VMO: VL amplitude ratio was significantly increased in both the EMS group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.37) and the HE group (P\u0026thinsp;=\u0026thinsp;0.018, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.30) at week 7 compared with that at week 0. The VMO: VL amplitude ratio was greater in the EMS group compared with those in the MST and HE groups (P\u0026thinsp;=\u0026thinsp;0.035, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.74; P\u0026thinsp;=\u0026thinsp;0.042, Cohen's \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.73) at week 7 (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study investigated the effects of a 6-week intervention involving EMS, MST, and HE on pain, knee function, muscle strength, muscle activations of VMO and VL and PFPS during running among people with PFP. The findings support the first hypothesis and partially support the second hypothesis.\u003c/p\u003e\u003cp\u003eThe results demonstrated that both EMS and MST were effective in relieving pain, improving knee function compared to HE among people with PFP. In addition, EMS demonstrating superior improvements in knee function compared with MST. These findings are consistent with previous studies. Bily et al. \u003csup\u003e[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e reported enhanced pain relief and functional recovery with the combination of exercise and electrical stimulation, while Paillard \u003csup\u003e[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/sup\u003ehighlighted the benefits of combining electrical stimulation with voluntary contractions compared to exercise alone. Glaviano and Saliba \u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e further supported these findings, noting that NMES combined with exercise alleviates pain, reduces muscle fatigue, and enhances neuromuscular adaptations, thereby improving muscle strength and compensation movement strategies.\u003c/p\u003e\u003cp\u003eThe observed benefits may be attributed to several mechanisms. Strengthening hip and knee musculature improves pelvic control, balances joint loading, and enhances lower limb stability \u003csup\u003e[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/sup\u003e. These adaptations reduce joint stress and friction and promote blood flow and tissue nutrition. Post-training stretching and relaxation further optimize soft tissue flexibility \u003csup\u003e[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/sup\u003e, thereby reducing abnormal tension and minimizing cartilage degeneration. NMES likely contributes to pain modulation through mechanisms such as the gate control theory \u003csup\u003e[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/sup\u003e and endorphin opioid release \u003csup\u003e[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]\u003c/sup\u003e. Additionally, NMES enhances microvascular perfusion and decreases capillary permeability \u003csup\u003e[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/sup\u003e, facilitating circulation and reducing edema. Collectively, these effects create a favorable biomechanical and physiological environment for joint recovery, which may account for the greater reductions in pain and enhancements in function observed in the EMS group.\u003c/p\u003e\u003cp\u003eRegarding muscle activation, both EMS and MST interventions improved knee extensor strength and VMO activation, with the EMS more effectively correcting imbalances between VMO and VL. Steadman \u003csup\u003e[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]\u003c/sup\u003e proposed that NMES enhances VMO motor unit recruitment, thereby restoring quadriceps force balance and improving patellar tracking. This aligns with evidence that the mechanism of action potentials involved in NMES is similar to that of voluntary muscle contraction. The current generated by neuromuscular electrical stimulation stimulates motor nerve axons and/or intramuscular nerve endings leading to changes in muscle membrane potential. This subsequently triggers calcium release, activates the signaling cascade, and ultimately induces skeletal muscle contraction \u003csup\u003e[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]\u003c/sup\u003e. Such rhythmic muscle contractions can increase motor unit recruitment and maintain sustained high-intensity firing rates, thereby generating greater force output and accelerate nerve regeneration \u003csup\u003e[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]\u003c/sup\u003e. The integration of NMES with voluntary contractions may further enhance spinal excitability and Ia reflex plasticity \u003csup\u003e[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]\u003c/sup\u003e, facilitating broader motor unit activation and greater force output. These mechanisms likely underpin the combined intervention\u0026rsquo;s superior efficacy in correcting muscle imbalances, which is essential for minimizing patellofemoral instability during weight-bearing activities.\u003c/p\u003e\u003cp\u003eAlthough both interventions reduced patellofemoral joint stress and increased quadriceps strength, no statistically significant differences were observed between the EMS and MST groups. Labanca et al. \u003csup\u003e[\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]\u003c/sup\u003e reported similar strength gains following eight weeks of NMES combined with resistance training compared to conventional training in patients with patellar tendinopathy. A meta-analysis by Hopp and WK. \u003csup\u003e[\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]\u003c/sup\u003e also found comparable improvements knee extension strength between NMES and traditional resistance training, suggesting a potential ceiling effect at approximately 70% one-repetition maximum (1RM) intensity \u003csup\u003e[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]\u003c/sup\u003e. Nevertheless, Martimbianco et al. \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e noted that combined training protocols specifically enhance VMO strength and correct medial-lateral imbalances, potentially reducing knee valgus and injury risk. The absence of intergroup differences in the present study may be attributable to suboptimal NMES dosage, an insufficient number of repetitions \u003csup\u003e[\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]\u003c/sup\u003e, or sex-related kinematic variations that may have influenced statistical power \u003csup\u003e[\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eSeveral limitations should be acknowledged. Heterogeneity in age, sex, injury severity, and etiology may influence the outcomes \u003csup\u003e[\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]\u003c/sup\u003e, and participant attrition limited the feasibility of subgroup analyses. Long-term follow-up was not conducted, precluding evaluation of sustained efficacy. Future studies should incorporate stratified analyses based on demographic and injury-related factors, extend the duration of interventions, and include post-rehabilitation monitoring to assess long-term effects. Despite these constraints, the findings underscore the clinical value of combining NMES with strength training for PFP management, particularly in optimizing functional recovery and addressing neuromuscular imbalances. Further research aimed at refining stimulation parameters and exploring individualized intervention protocols will enhance the development of evidence-based rehabilitation strategies.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study confirmed that a 6-week electrical stimulation combined with muscle strength training regime positively affected the symptoms by relieving pain, improving knee function, and balancing muscle activation of VMO and VL among individuals with PFP. Those observations support that EMS should be recommended as one of the clinical treatments for people with PFP.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003ePFP \u0026nbsp; Patellofemoral pain\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;PFJS \u0026nbsp; \u0026nbsp;Patellofemoral joint stress\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;VMO \u0026nbsp; \u0026nbsp;Vastus medialis oblique\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;VL \u0026nbsp; \u0026nbsp;vastus lateralis\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;NMES \u0026nbsp; \u0026nbsp;Neuromuscular electrical stimulation\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;MST \u0026nbsp; \u0026nbsp;Muscle strength training\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;HE \u0026nbsp; \u0026nbsp;health education\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;AKPS \u0026nbsp; \u0026nbsp;Anterior Knee Pain Scale\u003c/p\u003e\n\u003cp\u003e1RM \u0026nbsp; 1 repetition maximum\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;VAS \u0026nbsp; \u0026nbsp;Visual analog scale\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;EMG \u0026nbsp; \u0026nbsp;Electromyography\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e This study adheres to the CONSORT guidelines.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003cp\u003eThe study followed the institutional requirements and was approved by the Shandong Sport University Committee for Human Investigations (2022012), Prior to the study, the participants provided a written informed consent to participate.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003cp\u003e All participants in this study provided written informed consent for the publication of their personal and clinical details, as well as any identifiable images included in this study. All participants approved the submitted version of the manuscript for publication.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003ch2\u003eConflict of interest\u003c/h2\u003e\u003cp\u003eThe authors declare that they have no conflicts of interest relevant to the content of this article.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis work was supported by Tai 'an Central Hospital funded by the Shandong Provincial Traditional Chinese Medicine Science and Technology Project [M-2022080].\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by J.W. and YC.Y. The first draft of the manuscript was written by J.W. and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003e We express our gratitude to the Laboratory of Sports Biomechanics at Shandong Sport University for the technical support provided during data collection in this study; we also sincerely thank all participants for their full commitment to this research.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eHu H, Zheng Y, Liu X, Gong D, Chen C, Wang Y, Peng M, Wu B, Wang J, Song G, Zhang J, Guo J, Dong Y, Wang X. Effects of neuromuscular training on pain intensity and self-reported functionality for patellofemoral pain syndrome in runners: study protocol for a randomized controlled clinical trial. 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Med Sci Sports Exerc. 2012;44(11):2165\u0026ndash;71.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-musculoskeletal-disorders","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmsd","sideBox":"Learn more about [BMC Musculoskeletal Disorders](http://bmcmusculoskeletdisord.biomedcentral.com/)","snPcode":"","submissionUrl":"https://author-welcome.nature.com/12891","title":"BMC Musculoskeletal Disorders","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Anterior knee pain, Rehabilitation, Electrical stimulation, Patellofemoral joint stress","lastPublishedDoi":"10.21203/rs.3.rs-7611495/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7611495/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eObjective\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study aimed to investigate the effects of a 6-week muscle strength training combined with neuromuscular electrical stimulation on pain, function level, muscle strength, patellar stress, and muscle activation during running among individuals with patellofemoral pain (PFP).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study is a randomized, controlled, and assessor-blinded trial. Fifty-eight PFP participants were randomly assigned to the neuromuscular electrical stimulation combined with muscle strength training (EMS), conventional muscle strength training (MST) and health education (HE) groups. They received EMS, MST and health lectures series, respectively, for 6 weeks. Pain scores, knee function levels of anterior knee pain scale (AKPS), muscle strength of quadriceps, patellofemoral joint stress (PFJ), and muscle activation of vastus medialis oblique (VMO) and vastus lateralis (VL) during running were measured at week 0 and week 7, respectively. Two-way (group by time) ANOVA with repeated measures was used to evaluate training effects.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSignificant interactions were detected in pain score, AKPS, muscle strength, PFJ and muscle activation of VMO and VL. Compared with week 0, the pain score and PFJ decreased, whereas the AKPS, quadriceps muscle strength, muscle activation of VMO and VMO:VL ratio increased in EMS and MST groups at week 7. Additionally, the AKPS and muscle activation of VMO:VL ratio were significantly increased in the EMS group at week 7 compared with the MST and HE groups.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEMS could be recommended as one of the clinical treatments for PFP to relieve pain, improve knee function, and balance muscle activation of VMO and VL, thereby decrease patellofemoral joint stress during running.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTrial registration:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe effects of muscle electrical stimulation combined with muscle training on patients with joint pain and biomechanical characteristics of lower limbs, ChiCTR2300067598. Registered 13 January 2023, https://www.chictr.org.cn/showproj.html?proj=180778\u003c/p\u003e","manuscriptTitle":"Effects of muscle strength training combined with neuromuscular electrical stimulation on pain, function, muscle strength, patellar stress, and muscle activation during running in people with patellofemoral pain","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-10 15:35:08","doi":"10.21203/rs.3.rs-7611495/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-13T17:20:52+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-12T13:22:00+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"180587170332839588641944006782516036976","date":"2026-03-11T13:26:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"120927931105846119411403748575130017951","date":"2026-01-15T13:58:12+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-14T14:37:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"20449391154431357019023830486479576825","date":"2026-01-12T12:10:23+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-11T21:29:55+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"285203004159183909490142956114037049024","date":"2026-01-10T06:49:13+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-29T15:19:02+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"81409221417137853643753133622012522019","date":"2025-11-05T20:50:36+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-28T02:52:08+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-09-24T17:23:46+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-09-23T06:11:24+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Musculoskeletal Disorders","date":"2025-09-23T00:59:50+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-musculoskeletal-disorders","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmsd","sideBox":"Learn more about [BMC Musculoskeletal Disorders](http://bmcmusculoskeletdisord.biomedcentral.com/)","snPcode":"","submissionUrl":"https://author-welcome.nature.com/12891","title":"BMC Musculoskeletal Disorders","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a981ca57-3cd0-428c-8e5d-e9487728e208","owner":[],"postedDate":"October 10th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-10T14:53:11+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-10 15:35:08","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7611495","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7611495","identity":"rs-7611495","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}