Multiple sclerosis (MS) causes immune-mediated inflammation and neurodegeneration in the central nervous system, often leading to weakness and impaired mobility. In older adults with MS, it can be challenging to distinguish MS vs. age-related contributions to weakness. Studies are needed to examine the neuromuscular mechanisms of age-related declines in muscle strength to better understand their relative contribution to weakness in older adults with MS. To investigate the neuromuscular mechanisms underlying age-related declines in muscle strength and their contribution to weakness in older adults with MS. We conducted a study to determine whether older adults with MS exhibit differences in knee extensor voluntary (neural) activation, MRI-derived muscle volume, and skeletal muscle contractile quality compared to age-, sex-, and BMI-matched individuals without MS. Group comparisons were performed using nonparametric statistical analyses. In 10 older adults with MS and 10 age-, sex-, and BMI-matched controls, participants with MS had reduced isokinetic strength relative to body weight (MS 0.95 N·m/kg [0.77, 1.06], controls 1.48 N·m/kg [1.23, 1.66]) and summed torque relative to muscle volume (MS 10.31 × 103 N·m/cm3 [8.24 × 103, 11.84 × 103], controls 13.32 × 103 N·m/cm3 [12.50 × 103, 13.59 × 103]). In MS compared to controls, we also observed reduced peak isometric strength relative to muscle volume (MS 0.47 N·m/cm3 [0.37, 0.51], controls 0.58 N·m/cm3 [0.56, 0.63]) and reduced isokinetic strength relative to muscle volume (MS 0.37 N·m/cm3 [0.33, 0.42], controls 0.56 N·m/cm3 [0.52, 0.56]). Quadriceps muscle volume was similar in participants with MS (168.42 cm3 [158.55, 196.74]) and controls (183.26 cm3 [175.62, 202.25]). There was decreased neural activation parameters in MS including central activation ballistic torque (CAB) ratio (MS 0.31 [0.18, 0.35], controls 0.46 [0.40, 0.57]) and voluntary activation (MS 87.87% [84.09, 90.09], controls 94.82% [92.89, 95.78]). No statistically significant correlations between neuromuscular function and MS clinical outcomes were found. Neuromuscular function deficits in older adults with MS are largely attributed to impaired neural activation without significant differences in muscle quality compared with controls.

Predicting successful return to play (RTP) during mid-stage rehabilitation after anterior cruciate ligament reconstruction (ACLR) remains a critical, unresolved clinical challenge. High-sports demanders (HSDs)-non-professional athletes participating in level-1 sports (cutting, pivoting, jumping) ≥ 3 times/week with Tegner score > 5-represent a distinct subgroup who face unique rehabilitation challenges yet lack evidence-based mid-stage prediction tools. The primary objective of this study was to identify multidimensional predictors at 24 weeks post-ACLR for successful RTP at 48 weeks, and to construct a clinical scoring tool to guide individualized intervention decisions during mid-stage rehabilitation. This single-blind randomized controlled trial was conducted at the First Affiliated Hospital of Xi'an Medical University, Xi'an, China (April 2024-May 2025). Sixty-four HSDs post-primary ACLR were randomized to a functional rehabilitation model (FRM; n = 32) or traditional rehabilitation model (TRM; n = 32). At 24 weeks, isokinetic strength, hop tests, mSEBT, proprioception, and patient-reported outcomes (IKDC, Lysholm, ACL-RSI) were assessed. Forward stepwise logistic regression with bootstrap internal validation (1,000 iterations) identified independent predictors of 48-week RTP success. Among 57 completers (89.1% follow-up), the overall RTP rate was 75.4%. FRM significantly outperformed TRM (89.3% vs. 62.1%; P = 0.038; NNT = 3.7). Six independent predictors were identified: FRM vs. TRM (OR = 3.49), 60°/s extensor LSI ≥ 77.8% (OR = 2.13), single-leg hop ≥ 68.5 cm (OR = 1.87), ACL-RSI ≥ 67.5 (OR = 1.69), mSEBT anterior ≥ 63.2 cm (OR = 1.39), and 45° proprioceptive error ≤ 6.1° (OR = 0.62). Apparent AUC = 0.87 (95% CI: 0.79-0.95); bootstrap-corrected AUC = 0.81 (95% CI: 0.72-0.90). This exploratory six-factor model demonstrates promising discriminative ability (apparent AUC = 0.87; bootstrap-corrected AUC = 0.81) for mid-rehabilitation RTP prediction in HSDs. The identified predictive associations, rather than established causal relationships, may facilitate early risk identification and individualized intervention planning. External validation in independent, multicenter cohorts is required before clinical implementation.

Introduction: Anterior cruciate ligament (ACL) injuries in soccer players are multifactorial in nature, and the evaluation of isolated predictors (such as the isokinetic hamstring-to-quadriceps [H/Q] ratio) shows limitations in identifying risk profiles. Therefore, the integration of multiple neuromuscular variables into a predictive model is proposed to overcome these inconsistencies and improve injury risk screening. Objective: To analyze the association between neuromuscular imbalances, functional asymmetries, and performance parameters in jump tests with the risk of ACL injury in soccer players, and to develop a multivariable predictive model capable of identifying clinically relevant risk profiles. Methods: A cross-sectional study with an analytical approach was conducted with 60 male soccer players aged 18–28 years. Isokinetic strength (60°/s and 180°/s), concentric and eccentric H/Q ratios, peak power, reaction time, and jump performance (CMJ, SJ, DJ, and RSI) were assessed. Inter-limb asymmetries were calculated, and their association with confirmed history of ACL injury was analyzed using Pearson correlation and multivariable logistic regression. Results: The predictive model revealed that an eccentric H/Q ratio <0.85 (OR = 5.9), DJ asymmetry >10% (OR = 4.1), CMJ power <45 W/kg (OR = 2.4), and reaction time >130 ms (OR = 1.9) significantly increased the risk of ACL injury (AUC = 0.88; accuracy = 85.3%). Conclusion: The multivariable model confirms that ACL injury risk results from the convergence of eccentric deficits, functional asymmetries, and impaired neuromuscular control. The integration of these variables is essential for accurate risk screening.

Anterior cruciate ligament reconstruction (ACLR) is commonly performed in the younger or active population, but failure rates have been disappointing in high-risk patients. Recently, lateral extra-articular procedures such as the modified Lemaire extra-articular tenodesis (LET) have been proposed to decrease failure rates, but knowledge on short-term rehabilitation, stiffness, and isokinetic strength is limited. This study aimed to assess the short-term patient-reported outcome measures (PROMs) and physical performance outcomes following ACLR with and without LET. A prospective study was performed among 152 patients aged ≤25 years undergoing hamstring autograft ACLR with or without modified Lemaire LET between 2019 and 2022 with minimum 1-year follow-up. PROMs (Tegner, International Knee Documentation Committee, Lysholm, NRS for pain, and EQ-5D) were compared between groups preoperatively and at 3, 6, 9, 12, and 24 months, while physical performance (range of motion [ROM], and limb symmetry indices [LSI] of isokinetic testing, single-leg and timed-6m hop) was compared up to 9 months postoperatively. Baseline characteristics and outcomes were similar, except thicker grafts in the LET group (8.9 vs. 8.7 mm, p = 0.047). At 3 months, Lemaire patients reported less pain (NRS pain 17.1 vs. 35.6, p < .001), but at 6 months, Lemaire patients had inferior LSI for timed-6m hop (87% vs. 96%, p = 0.003). At 9 months, Lemaire patients had similar return to sports, PROMs, and ROM, but had lower LSI for flexion endurance strength (88% vs. 97%, p = 0.041). At 12 months, no differences were seen in PROMs. In conclusion, Patients undergoing ACLR with LET had less pain at 3 months, but worse LSI for timed-6m hop at 6 months and worse LSI for flexion endurance strength at 9 months. Both groups showed similar performance on all other outcomes, indicating that ACLR with LET is not associated with increased stiffness, complications, or significant strength deficits. LEVEL OF EVIDENCE: : Level II prospective study.

To compare body composition, muscle performance, and muscle quality across age and sex groups. A cross-sectional analytical study was conducted in healthy-self-referred adults stratified in age groups: 18-35, 50-64, and ≥65 years. Evaluations included BMI (kg/m2), DXA-derived body composition (ALM, kg; body-fat, %), handgrip-dynamometry, and isokinetic knee-extensor testing concentric/eccentric low/high angular velocities. MQIs were calculated as force normalized to LM. Group comparisons, effect sizes, and correlation analyses were performed. Statistical significance was set at p < 0.05. A total of 152 adults were analyzed. Body composition showed significant age-related differences, with increased body-fat percentage from young to middle adulthood and reduced ALM in older adults, while BMI showed limited discriminatory capacity. Handgrip-strength declined significantly only in the oldest group and showed small effect sizes after normalization by body-weight. In contrast, isokinetic knee extensor strength (particularly high-velocity concentric-torque) demonstrated pronounced age-related declines with moderate-to-large effect sizes. Eccentric/concentric torque ratios increased with age, indicating relative preservation of eccentric strength. Handgrip-based MQIs showed no age-group discrimination, whereas isokinetic-derived MQIs did. Muscle aging is characterized by early adiposity increase and later deterioration of lower-limb, velocity-dependent muscle performance, better captured by isokinetic-based measures than by BMI or handgrip-derived indices.

The effect of exercise rehabilitation on bone mineral density, muscle strength, and physical function outcomes in ACL ruptures: A randomized controlled clinical trial.

This study examined alterations in ankle eversion/inversion strength and postural control in chronic lateral ankle instability (CLAI). Twenty-three CLAI patients and 14 matched controls underwent isokinetic strength testing at 30°/s, 60°/s, and 90°/s (peak torque/body weight: PT/BW). Postural control was assessed via center-of-pressure (COP) trajectory length and peripheral area during eyes-open and eyes-closed single-leg stance. The CLAI group demonstrated significantly lower eversion PT/BW across all angular velocities versus controls (p<0.05). Inversion PT/BW was not significantly different for the group effect (p>0.05). The eversion-to-inversion strength ratio was consistently lower in CLAI (p<0.05). No between-group differences in COP metrics occurred during eyes-open stance (p>0.05). However, with eyes closed, the CLAI group exhibited significantly longer COP trajectory [107.52 (94.90,118.70) cm vs. 93.75 (83.09,95.25) cm] and larger peripheral area [8.34 (5.73,12.90) cm2 vs. 5.92 (5.05,6.88) cm2] (p<0.05). CLAI is characterized by eversion muscle weakness and an impaired eversion-to-inversion strength ratio. Postural control deficits manifest primarily under visual deprivation, suggesting proprioceptive impairment, though visual input enables partial compensation during eyes-open conditions.

Lateral extra-articular tenodesis (LET) has been shown to improve rotational stability and clinical outcomes and to reduce graft failure rates in selected high-risk patients. However, the comparative effects of deep (beneath-LCL) and superficial (over-LCL) LET techniques on clinical and biomechanical outcomes remain uncertain. This study aimed to compare the functional, kinematic, and strength outcomes of deep and superficial LET performed concomitantly with ACLR in patients with high-grade pivot-shift. It was hypothesised that superficial LET would result in clinical and biomechanical outcomes comparable to those of the deep LET technique. This prospective, randomised, double-blind comparative study included 24 male patients with isolated ACL rupture and pivot-shift grades 2-3. Patients were divided equally into two treatment groups as ACLR with deep LET or superficial LET. All procedures used standardised quadrupled hamstring autografts. Clinical outcomes were assessed using the IKDC, Lysholm, and Tegner scores preoperatively and at 6 and 12 months. Biomechanical assessments included three-dimensional running gait analysis and isokinetic tibial rotation strength testing at 6 months postoperatively. All patients completed follow-up with no graft ruptures. Both groups showed significant improvement in IKDC and Lysholm scores at 6 and 12 months (p < 0.05). The deep LET group demonstrated greater improvement in IKDC (86.5 ± 3.0 vs. 81.3 ± 6.7, p = 0.022) and Lysholm (90.8 ± 2.9 vs. 85.8 ± 7.2, p = 0.037) scores. Running gait analysis revealed reduced stance phase tibial rotation (p = 0.035) and anterior translation (p = 0.01) in the deep LET group, indicating superior dynamic control. Isokinetic torque recovery and Tegner activity levels (6.4 vs. 6.0, p = 0.19) were comparable. Concomitant deep and superficial LET techniques effectively restored knee stability and improved clinical outcomes after ACL reconstruction. However, the deep LET technique was associated with improved tibial rotational stability and more favourable patient-reported outcomes in young, athletic male patients with high-grade pivot-shift. Level 1, randomised controlled trials with adequate statistical power to detect differences (narrow confidence intervals) and follow up >80%.

The R577X polymorphism in the α-actinin-3 gene (ACTN3) influences the expression of α-actinin-3, and previous studies have reported its association with muscle strength and power performance. This systematic review and meta-analysis aimed to clarify the relationship between the ACTN3 R577X polymorphism and various indicators of muscle strength and power. A systematic search of PubMed and Web of Science was conducted on 15 October 2025, and studies were included if they were published in English, involved healthy human participants, assessed muscle function, and analyzed the ACTN3 R577X genotype. Muscle function outcomes examined in this review included maximum voluntary contraction, one-repetition maximum, isokinetic strength, jump performance, sprint performance, Wingate test, chair stand test, and walking test. Fifty-three articles were included in the meta-analysis. One-repetition maximum, maximum voluntary contraction and jump performance showed a significant association with the ACTN3 R577X polymorphism in the additive model and were higher for the RR, RX and XX genotypes (one-repetition maximum: p = 0.005, maximum voluntary contraction: p = 0.006, and jump performance: p = 0.003). There was no significant association between the ACTN3 R577X polymorphism and other measurements. This study suggests that the ACTN3 R577X polymorphism is associated with one-repetition maximum, maximum voluntary contraction, and jump performance in the additive model and the impact may be stronger among men.

The study aim was to compare lower extremity muscle strength measurements obtained during the quadriceps set exercise in healthy individuals. Twenty-four healthy individuals (23.1±2.1 years, 13 females) were recruited. Lower extremity muscle strength measurements were obtained using a hand-held dynamometer during the quadriceps set exercise and using an isokinetic dynamometer with isometric testing at 30° of knee flexion and at 60°/s concentrically. Validity was assessed using Pearson correlation and Bland and Altman analyses, while within-session reliability was assessed using the Intraclass Correlation Coefficient (ICC). Also, standard error of measurement (SEM%), minimal detectable change (MDC95) and minimal important change (MIC95) at the 95% confidence interval were assessed. Hand-held dynamometer measurements during the quadriceps set exercise were strongly correlated with isometric measurements at 30° of knee flexion (r=0.598, p=0.002) and concentric measurements at 60°/s (r=0.535, p=0.007) on the isokinetic dynamometer. The hand-held dynamometer demonstrated a good within-session reliability (ICC=0.88, 95%CI:0.80–0.94), while the isometric measurements at 30° of knee flexion (ICC=0.91, 95%CI:0.85–0.95) and the isokinetic measurements at 60°/s (ICC=0.92, 95%CI:0.86–0.96) demonstrated an excellent within-session reliability. Across all measurements, SEM% values ranged between 9–11%. The MDC95 was calculated as 5.97 (95%CI:3.5–8.5) for the hand-held dynamometer, 34.25 (95%CI:16.9–51.8) for the isometric measurements at 30° of knee flexion, and 40.0 (95%CI:20.8–59.3) for the isokinetic measurements at 60°/s. The MIC95 values corresponded to an approximate change of 14% for the hand-held dynamometer and 19% for the isokinetic dynamometer relative to the mean muscle strength values of healthy participants. These findings indicate that the use of the hand-held dynamometer as a measurement method in the quadriceps set exercise position is valid and reliable, and it may serve as a viable alternative to isokinetic testing, particularly in the early postoperative phase when isokinetic strength assessment is often considered unsafe.

Quadriceps atrophy and post-operative pain are common following anterior cruciate ligament reconstruction (ACLR) and can hinder functional recovery. This study aimed to systematically compare the effectiveness of neuromuscular training (NMT), virtual reality training (VRT), proprioceptive training (PT), blood flow restriction training (BFRT) and conventional rehabilitation training (CRT) in individuals undergoing rehabilitation after ACLR. A systematic review and network meta-analysis (NMA) were conducted in accordance with PRISMA-NMA guidelines. Six databases (PubMed, EMBASE, Cochrane Library, Web of Science, CNKI and Wanfang) were searched for randomized controlled trials (RCTs) published up to 1 May 2025. Risk of bias was assessed using the Cochrane RoB 2.0 tool. A frequentist NMA was performed in Stata 17.0MP to estimate standardized mean differences (SMDs) and 95% confidence intervals (CIs). Interventions were ranked using surface under the cumulative ranking curve (SUCRA) values. The certainty of evidence was appraised using the CINeMA framework. Twenty-two RCTs involving 972 participants (mean age 23-39 years) were included. Compared with CRT, VRT showed favourable outcomes in visual analogue scale for pain (SMD = -0.72, 95% CI = [-1.22 to -0.22], SUCRA = 86.5%), functional hop tests (SMD = 1.26, 95% CI = [0.46-2.05], SUCRA = 97.5%) and isokinetic muscle strength (60°/s) (SMD = 2.24, 95% CI = [1.28-3.20], SUCRA = 99.6%). BFRT also outperformed CRT in several outcomes, including the International Knee Documentation Committee Subjective Knee Evaluation Form (SMD = 1.37, 95% CI = [0.77-1.96], SUCRA = 81.8%), Lysholm Score (SMD = 1.07, 95% CI = [0.16-1.97], SUCRA = 74.7%) and knee range of motion (SMD = 1.42, 95% CI = [0.80-2.04], SUCRA = 99.1%), with relatively high SUCRA values. Compared with CRT, NMT demonstrated modest improvements in the Functional Hop Tests (SMD = 0.29) and the Lysholm Score (SMD = 1.00). Certainty of evidence ranged from moderate to low, primarily due to imprecision and risk of bias. VRT and BFRT may offer benefits across several domains of post-operative rehabilitation following ACLR, with NMT also showing potential. However, given the limitations in evidence certainty, further high-quality RCTs are warranted to confirm these findings and inform clinical practice. Level I.

Upper extremity return to sport (RTS) assessments are not standardized with respect to which metrics to use, if the metrics are appropriate for all populations and levels of competition, and what constitutes good or poor test performance. Subsequently, clinicians may utilize suboptimal metrics to evaluate RTS readiness, or forgo objective criteria altogether. The purpose of this study was to examine the psychometric properties (reliability, agreement/measurement error, hypothesis testing/construct validity, criterion/predictive validity, responsiveness) of upper extremity functional tests used to assess RTS readiness. This systematic review followed PRISMA guidelines, with all studies included assessed via the PEDro scale. Literature searches covering PubMed, Google Scholar and Medline databases were completed through November 2024. Studies focusing on the reliability and/or validity of upper extremity functional tests in athletes were included. A total of 5166 studies were identified; 60 studies met criteria for data extraction. Among the identified tests, the Single Arm Shot Put test (SASP), Closed Kinetic Chain Upper Extremity Stability Test (CKCUEST), and the Upper Quarter Y-Balance test (UQY) were the most frequently investigated. The SASP emerged as consistently reliable (the preponderance reporting ICC > 0.90), with construct validity evidenced by correlations with upper extremity isokinetic torque and performance on other functional tests. The CKCUEST demonstrated good to excellent reliability across age, sex, and sport, including individuals with shoulder pain (ICC = 0.73-0.98). Construct validity was established via strong correlations with grip and isokinetic upper extremity strength (P < 0.01), and concurrent validity when compared to other upper extremity functional tests. The CKCUEST also demonstrates predictive validity for determining future upper extremity injury risk, and discriminant validity distinguishing individuals with and without current shoulder injury. The UQY yielded mixed reliability, with ICC = 0.47-0.97; additionally, numerous studies found no significant relationships between the UQY and other measures (strength and/or other upper extremity functional tests). The athletic shoulder test (ASH) is an emerging test designed to evaluate isometric strength of the upper body in 3 positions with the athlete prone. Across all testing positions, the ASH has excellent test-retest reliability (ICCs ranging from 0.94 to 0.98), and has demonstrated high concurrent validity when a sphygmomanometer or hand-held dynamometer is utilized instead of a force plate. This is the first extensive systematic review examining the psychometric properties of commonly administered upper extremity functional tests used to determine RTS criteria, with 60 articles analyzed. The CKCUEST and SASP demonstrate consistent reliability and validity across multiple athletic populations. Understanding strengths and limitations of upper extremity functional tests aids clinicians in choosing appropriate assessments for RTS across age, sex, sport, and level, as well as healthy and injured athletes.

The relationship between kyphosis, and shoulder pain is unclear, and the effects of kyphosis angle on pain severity, range of motion, isokinetic strength, and upper extremity functionality remain undetermined. This study aimed to investigate the correlation between increased thoracic kyphosis and these factors. Thirty participants with a thoracic hyperkyphosis (a mean thoracic kyphosis angle of 57.47 ± 9.96°) were included in the study. The thoracic kyphosis angle was measured using a manual inclinometer. Shoulder pain severity was assessed with the Visual Analog Scale (VAS), shoulder range of motion was evaluated using a manual goniometer, shoulder isokinetic muscle strength was measured with an isokinetic dynamometer, and upper extremity functionality was assessed using the Quick Disabilities of the Arm, Shoulder, and Hand (QuickDASH) questionnaire. Significant correlations were observed between thoracic kyphosis angle and both VAS scores and QuickDASH scores. In addition, the thoracic kyphosis angle was negatively correlated with shoulder flexion, abduction, and external rotation range of motion, as well as internal rotation peak torque. No significant correlations were found between thoracic kyphosis angle and the remaining isokinetic muscle strength parameters. Greater thoracic kyphosis angles were associated with increased shoulder pain severity and reduced shoulder flexion, abduction, and external rotation range of motion, decreased internal rotation peak torque, and impaired upper extremity functionality. These findings suggest that interventions aimed at reducing thoracic kyphosis may contribute to improvements in shoulder pain severity and upper extremity function, potentially through enhancements in joint range of motion and isokinetic muscle strength. The protocol is registered with http://clinicaltrials.gov/ (Retrospectively registered, Clinical Trial, NCT07349238.

Abstract Introduction: Adjuvant chemotherapy (AdjCTx) in breast cancer patients is associated with muscle weakness, fatigue, and functional decline that may persist into survivorship. While exercise is recognized as a supportive intervention, the role of circuit-based exercise (CBE) during active chemotherapy remains underexplored. This study investigated the feasibility and functional outcomes of a supervised CBE program in breast cancer patients with or without concurrent AdjCTx. Methods: This study included 40 postoperative breast cancer patients who completed a CBE program for at least two months between June 2020 and April 2023. Patients were stratified into AdjCTx (+) (n = 20) and AdjCTx (-) (n = 20) groups. The CBE protocol, delivered via the Milon® system, integrated aerobic and eccentric resistance training at 60% of one-repetition maximum. Functional outcomes included isokinetic knee extensor strength (peak torque), gait speed (10-meter walk test), balance (Berg Balance Scale), and mobility (Timed Up and Go). Body composition was assessed using bioelectrical impedance analysis. Within-and between-group changes were analyzed using repeated measures ANOVA and paired t-tests. Results: Both groups demonstrated significant improvements in knee extensor strength over time (P &amp;lt;0.05), with significant time effects (F = 10.75-12.34, P &amp;lt; 0.001). The AdjCTx (-) group demonstrated greater absolute gains, while the AdjCTx (+) group showed steady, progressive improvements without regression. BMI significantly decreased in both groups (P&amp;lt;0.001); changes in body fat percentage and ALMI were not statistically significant. Functional improvements in TUG and BBS were observed only in the AdjCTx (-) group (P&amp;lt;0.05), whereas the AdjCTx (+) group maintained baseline function. Gait speed improved significantly in both groups, with a greater increase in the AdjCTx (+) group (P=0.022), despite persistent strength deficits. Conclusions: CBE incorporating eccentric resistance is a feasible and well-tolerated during AdjCTx. It preserves lower-limb strength and functional capacity, highlighting its potential as an early, structured rehabilitation strategy to counteract treatment-related decline and support long-term survivorship in breast cancer patients. Citation Format: K. Cho, E. Han, S. IM. Impact of circuit based exercise in breast cancer survivorship [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-05-17.

To explore the potential correlational patterns between lower extremity explosive power, strength balance, joint stiffness, neuromuscular characteristics and running economy (RE) as well as personal best (PB) of long-distance runners under different relative paces, so as to provide a preliminary theoretical clues for optimizing endurance training. Ten male second-class long-distance runners were recruited. Under the paces of PB70%, PB80% and PB90%, RE, maximal oxygen uptake (VO2max), lower extremity explosive power (CMJ, SJ, EUR, RSI), joint peak torque ratio (PTR), joint stiffness and neuromuscular indicators (RMS, CAR) were tested using gas metabolism analysis, force platform, isokinetic strength testing system, motion capture system and electromyography equipment. Data were processed by one-way repeated measures analysis of variance, paired samples t-test and Pearson correlation analysis. RE increased significantly with the increase of pace (p < 0.05), and the correlation between RE and PB at PB80% and PB90% was stronger than that between VO2max and PB; RSI was significantly negatively correlated with RE70%, RE90% and PB (p < 0.05), while CMJ, SJ and EUR had no significant correlation; at 180°/s angular velocity, the hip joint flexor eccentric-extensor concentric PTR was significantly positively correlated with RE70%, RE90% and PB, and the knee joint flexor concentric-extensor eccentric PTR was significantly positively correlated with RE at all paces and PB (p < 0.05); knee joint stiffness was significantly negatively correlated with RE at all paces (p < 0.05); the RMS of vastus medialis (VM) was significantly positively correlated with RE70% and RE90%, and the knee joint CAR was significantly negatively correlated with RE at all paces (p < 0.05). This study is strictly exploratory and hypothesis-generating. RE is a core indicator potentially associated with long-distance running performance. RSI, specific hip and knee PTR at 180°/s angular velocity, knee joint stiffness and knee joint neuromuscular activation characteristics (VM RMS, knee joint CAR) show potential correlational associations with RE. The associations between these indicators and RE are pace-dependent and joint-specific, which can provide preliminary scientific reference for generating hypotheses about long-distance running training.

Changquan (Long Fist) is a competitive martial arts discipline characterized by complex offensive and defensive techniques requiring high levels of coordination, agility, and strength. The knee joint, as the central link between the upper and lower limbs, plays a vital role in generating power and maintaining movement stability. This study investigated the relationship between knee joint muscle strength and agility among competitive Changquan athletes. A mixed-method design involving literature review, expert interviews, questionnaire survey, and experimental testing was employed. Twelve male Changquan athletes underwent bilateral isokinetic knee strength assessments at angular velocities of 60°/s (maximal strength) and 240°/s (explosive strength) using a Biodex System 4 Pro dynamometer. Peak torque (PT), relative peak torque (PT/BW, %BW), flexor-extensor ratio (F:E), total work (TW), and endurance ratio (ER) were recorded. Agility was evaluated using the T-test and 15 s push-up test. Pearson correlation analysis examined relationships between strength and agility parameters. Results showed that knee extensor strength exceeded flexor strength, with mean peak torque values of 236.39 ± 17.62 N·m and 131.99 ± 13.54 N·m at 60°/s, and 133.85 ± 12.47 N·m and 97.85 ± 10.61 N·m at 240°/s. The right side was slightly stronger, though differences were not significant (p > 0.05). Athletes achieved excellent agility scores (T-test: 9.31 ± 0.16 s; push-ups: 9.66 ± 0.89 reps). Strong positive correlations were found between agility and slow flexor peak torque (r = 0.699, p = 0.011), slow extensor relative peak torque (r = 0.578, p = 0.049), and total work of slow flexors (r = 0.619, p = 0.032). The degree of correlation with agility followed the order: maximal strength > explosive power > strength endurance. Competitive Wushu Changquan athletes possess relatively balanced bilateral knee muscle strength; however, the flexor muscles are comparatively weaker, which may increase the risk of sports injury. Knee joint muscle strength particularly maximal and explosive flexor capacity is a key determinant of agility in competitive Wushu Changquan athletes. Balanced enhancement of flexor and extensor strength is recommended to improve performance efficiency, technical execution, and injury prevention. These findings provide a scientific basis for optimizing strength and conditioning programs for Changquan athletes through targeted flexor-extensor development to improve agility, performance precision, and injury prevention.

ABSTRACT Context The highest incidences of musculoskeletal (MSK) injuries within the military occur at anatomical regions most impacted by jumping and landing, including the knee. Military personnel assigned to Special Operations Forces (SOF) are at particularly high risk of MSK injury due to occupational demands. Objective To characterize changes in limb loading symmetry during walking gait from 6 to 12 months after ACLR in patients with extensor mechanism autografts using force-sensing insoles, and to compare the change in limb loading metrics between patients with bone-patellar tendon-bone (BPTB) and quadriceps tendon (QT) autograft. Design Cross-Sectional Study Setting Laboratory Patients or Other Participants Two hundred twenty-four uninjured active-duty male SOF personnel (age = 27.7 ± 5.0 years; mass = 83.1 ± 9.1 kg; height = 176.5 ± 5.7 cm) completed biomechanical analyses of two different drop landing tasks (double leg (DLDL) and single leg (SLDL)) and isokinetic strength testing of the quadriceps and hamstrings. Main Outcome Measure(s) Peak hip, knee, and ankle angles; hip, knee, and ankle angles at initial ground contact (@IC); and peak vertical ground reaction (VGRF) forces were identified during landing tasks. Maximum voluntary isokinetic knee extension strength (KES) and knee flexion strength (KFS) were also assessed. Results Participants demonstrated greater KES with their dominant limb by an average of 0.06 Nm/kg (p=0.001, d=0.219) and landed with greater force on the dominant limb during DLDL by an average of 20% bodyweight (p&lt;0.001, d=0.377). No asymmetries involving knee kinematics were identified. During DLDL, both limbs demonstrated similar significant correlations between knee (peak) and ankle (@IC and peak) kinematics and peak VGRF. During nondominant SLDL, knee@IC, peak knee flexion, and peak dorsiflexion significantly correlated to peak VGRF. Peak knee flexion during non-dominant SLDL correlated to non-dominant KES. Conclusions Knee mechanics are important components for shock attenuation, but for this population, factors other than strength likely play a more significant role in controlling the mechanics about the knee during landing tasks.

Background/Objectives: Persistent strength deficits and psychological impairments may compromise return to sport (RTS) after anterior cruciate ligament reconstruction (ACLR). We investigate the relationship between thigh muscle isokinetic strength recovery at six months after ACLR and long-term psychological outcomes related to RTS in competitive male soccer players. Methods: Sixty male soccer players who underwent primary ACLR with bone-patellar tendon-bone autograft were retrospectively analyzed. Isokinetic testing of quadriceps and hamstrings was performed one week before surgery and six months post-surgery at 90°/s and 180°/s. Limb symmetry index (LSI) was calculated both pre- and post-operatively. At long-term follow-up (mean ≈ 4 years after RTS), athletes completed questionnaires assessing RTS status, ACL re-injuries, sport-related perceptions, and kinesiophobia using the Tampa Scale for Kinesiophobia (TSK). Statistical analyses were conducted to explore associations between post-operative LSI and TSK scores and to compare psychological and neuromuscular outcomes between athletes with and without ACL re-injury. Results: Absolute quadriceps and hamstring peak torque values significantly increased from pre- to post-surgery, with quadriceps strength deficits persisting only in the operated limb. However, quadriceps LSI significantly decreased post-operatively, while hamstring LSI remained stable. Pearson correlation analysis revealed a weak positive association between post-operative quadriceps LSI at 90°/s and TSK scores (r = 0.34). Overall, RTS rate was 91.7%, but a second ACL injury occurred in 18.2% of athletes. No significant differences were observed between re-injured and non-re-injured athletes in TSK scores or post-operative LSI values at either angular velocity (all p > 0.29). High kinesiophobia (TSK ≥ 37) was present in 56.7% of the cohort at long-term follow-up. Conclusions: Despite significant strength gains, quadriceps limb symmetry worsened six months after ACLR, with deficits confined to the operated limb, suggesting persistent neuromuscular inhibition. These physical deficits coexist with long-term kinesiophobia despite high RTS rates. The weak associations between strength symmetry and psychological outcomes highlight the multifactorial nature of RTS and support the need for an integrated physical, psychological, and neuro-cognitive approach to rehabilitation and RTS decision-making.

BackgroundReactive strength index (RSI) derived from single-leg vertical continuous jumps (SVCJ) is a low-cost method to assist in making return-to-sport (RTS) decisions after anterior cruciate ligament reconstruction (ACLR); however, its relationship with isokinetic knee strength at different postoperative time points remains unclear. The purpose of this study was to explore the relationship between the RSI during SVCJ and isokinetic knee muscle strength in patients five to eight months after ACLR.Study designRetrospective cohort studyMethodsPatients who had undergone primary ACLR with hamstring tendon autografts were enrolled. At five, seven, and eight months postoperatively, the participants performed 15 SVCJ recorded on an iPad at 240 fps. RSI was calculated as jump height divided by ground contact time, with flight time and contact time derived from video analysis using a validated smartphone/tablet application. Isokinetic peak knee extension and flexion torques were measured bilaterally at 60°/s using the Biodex System 3. Limb symmetry index (LSI) was calculated for both isokinetic knee strength and RSI as (operated limb value / non-operated limb value) × 100 (%). Time effects were analyzed using repeated-measures analysis of variance, and Pearson correlations assessed associations between RSI and knee strength.ResultsTwelve competitive athletes (mean age, 34.3 ± 11.3 years), participating in cutting- and jumping-based sports were analyzed. Isokinetic knee flexion peak torque significantly improved from five to eight months (p < 0.05) postoperatively. The extension-strength LSI was 75% at eight months, whereas the flexion-strength LSI increased from 84.5% at five months to 93.5% at eight months. The RSI LSI reached 83.1% at eight months. Correlations between RSI and knee extension strength were strong and significant at five months (r = 0.81, p < 0.01) and seven months (r = 0.91, p < 0.01) but were weak and not significant at eight months (r = 0.36, p = 0.26).ConclusionRSI may serve as a surrogate for isokinetic knee extension strength during midterm rehabilitation after ACLR, later reflecting higher-order explosive performance; smartphone/tablet-based assessment supports staged RTS decision making.Level of Evidence2b

Adolescent baseball pitchers are vulnerable to upper-extremity injuries because of the repetitive, high-stress nature of throwing movements. While shoulder strength and range of motion (ROM) are commonly measured, they are often interpreted in isolation during injury prevention assessments. To determine the relationship between clinical measures (shoulder ROM and strength) and throwing arm joint kinetics in adolescent baseball pitchers. Descriptive laboratory study. This study was conducted in a laboratory setting. A total of 43 adolescent baseball pitchers (age, 15-18 years) were recruited through convenience sampling. Participants underwent clinical assessments of shoulder ROM and isokinetic concentric strength testing. Pitching biomechanics were analyzed to obtain elbow valgus torque, shoulder distraction force, shoulder internal rotational (IR) torque, and ball velocity. A stepwise linear regression analysis was performed to assess shoulder strength and ROM as predictors of pitching kinetics and ball velocity. A stepwise regression analysis showed that elbow valgus torque (92.1 ± 24.9 N·m) was positively associated with increased shoulder IR strength at 60 deg/sec and negatively associated with total arc ROM (IR strength, 68.3 ± 17.3 N·m; total arc, 172.8°± 19.2°; adjusted R 2 = .258; P < .001). Peak shoulder distraction force (1238.9 ± 361.2 N) was positively associated with shoulder external rotation (ER) strength at 60 deg/sec (41.3 ± 10.8 N·m; β = .465; adjusted R 2 = .197; P = .002). Peak shoulder IR torque (113.7 ± 37.4 N·m) was positively associated with shoulder IR strength (β = .421; adjusted R 2 =.157; P = .005). Higher ball velocity (125.9 ± 8.7 km/h) was linked with higher shoulder IR strength (β = .390; adjusted R 2 =.131; P = .010). There were moderate to strong positive relationships between ball velocity and pitching kinetics (Pearson's r value: valgus torque, 0.603; distraction force, 0.594; shoulder IR torque, 0.865; P < .001). Pitchers with greater shoulder IR strength and reduced total arc ROM demonstrated increased elbow valgus torque at maximal shoulder ER during pitching. Although IR strength is crucial for generating ball velocity, maintaining total arc ROM within an optimal range will help reduce elbow joint stress. In addition, shoulder ER was positively associated with peak shoulder distraction force. Monitoring ER strength may help identify potential fatigue or imbalance, allowing for timely clinical attention.