Search Results (133)

Background: Curve sprinting in the 200 m dash entails distinct biomechanical requirements under strenuous anaerobic conditions that differ from sprinting on the straightway. This study aimed to examine possible relationships between anaerobic biomarkers (specifically, peak post-test blood lactate concentration; BLa) and step kinematic asymmetry, stance-phase biomechanics, and spring–mass model (SMM) variables at the curve-to-straight transition during a 200 m sprint. Methods: Sixteen adult male club- and national-level sprinters performed a maximal 200 m sprint test in this exploratory cross-sectional study. Kinematical data were recorded for the first step immediately after the geometric end of the curve, and peak BLa was measured at 3, 5, and 7 min post-test. Based on data normality, differences in inter-limb step parameters were examined using a paired t-test or Wilcoxon signed-rank test. Pearson’s and Kendall’s correlation coefficients evaluated the relationships between BLa and the biomechanical variables (significance level: a = 0.05). Results: Peak BLa was 16.16 ± 2.61 mmol/L and demonstrated no significant correlation (p > 0.05) with sprint time (24.89 ± 1.24 s). Only stride and step frequency during the outer-to-inner leg step was correlated (p < 0.05) with BLa. Furthermore, the step initiated by the outer leg had a larger length (p < 0.05) compared to the step length generated from the inner leg. Conclusions: These findings stem from the different roles between legs while handling the centripetal force requirements during curve sprinting. The outer leg generated a longer step to facilitate curve-to-straight transition, whereas the inner leg functioned primarily to stabilize and steer the body. Full article

Interlimb asymmetry is relevant for monitoring neuromuscular function in athletes, but evidence on futsal-specific preventive strategies in youth players remains limited. This study examined the effects of a 20-week Futsal Preventive Program (FPP) on functional interlimb asymmetry and explored injury risk during a 9-month surveillance period. Sixty-seven youth male outfield players completed pre- and post-intervention assessments (control group, n = 36; experimental group, n = 31), while 79 players were included in the injury-risk analysis (control group, n = 41; experimental group, n = 38). The experimental group performed a 15 min neuromuscular warm-up weekly, while the control group continued its usual warm-up. Asymmetry was assessed using countermovement jump (CMJ), horizontal jump (HJ), and 505 change-of-direction (COD 505) tests. The program produced a task-specific reduction in COD 505 asymmetry compared with the control group (cluster-adjusted difference = −1.27 percentage points; 95% CI: −2.00 to −0.53; Bonferroni-adjusted p = 0.03), whereas no significant intervention effects were observed for CMJ or HJ asymmetry. Across the full 9-month surveillance period, the crude cumulative injury-risk estimate was RR = 0.92 (95% CI: 0.59–1.45), with the confidence interval including the null value. These findings support a task-specific effect of the FPP on COD 505 asymmetry, without evidence of corresponding effects on CMJ or HJ asymmetry. Injury findings were descriptive and hypothesis-generating and do not establish preventive efficacy. Further studies with a larger number of randomized teams, greater weekly intervention exposure, and individual training and match exposure monitoring are warranted to clarify potential effects on injury incidence. Full article

Neurological disorders drive demand for prolonged upper-limb rehabilitation, yet specialist access is uneven and assessment stays subjective. Marker-based and inertial measurement unit (IMU) systems are accurate but costly and impractical at home, while pose estimation pipelines mostly stop at keypoints, and many process video server-side, raising privacy concerns. We present a markerless pipeline that analyzes monocular RGB video entirely on-device in the browser, so it never leaves the machine. From 33 BlazePose keypoints, it derives five geometric metrics designed to limit body-size dependence—incomplete elbow extension, inter-limb asymmetry, shoulder girdle elevation, lateral trunk lean, and head tilt—compared against empirically calibrated, preliminary thresholds; a finite-state machine segments repetitions, and the flags are pooled into an unvalidated, exploratory quality score. Against an IMU reference over the 0–${62}^{\circ }$ range that the recordings cover, the image-plane angle showed a mean absolute error of ${2.18}^{\circ }$, below the pre-specified $5^{\circ }$ tolerance, a trajectory-averaged bias within $\pm 2^{\circ }$, and Lin’s concordance correlation coefficient of $0.956$; the difference is, however, proportional to the angle—about $4\%$ of the measured value—so the accuracy should not be extrapolated to larger elevations, and because that comparison was made offline, it does not include the timing error of the causal real-time path. On a single seated frontal-plane abduction task, with 18 healthy volunteers simulating the compensations and annotated by two independent clinicians blind to the instructed condition, compensation detection reached a macro-averaged $F_1$ of $0.75$ and $0.72$ against the individual raters. The five signs differ in maturity: near-expert for trunk lean and head tilt, moderate for incomplete elbow extension and inter-limb asymmetry, and weakest for shoulder elevation, which a single frontal view cannot fully disentangle from the abduction motion. Running at 22–30 frames per second on consumer laptops without relying on a discrete GPU, it offers an accessible, privacy-preserving proof-of-concept foundation for home telerehabilitation; generalization beyond this one exercise and effectiveness on genuine post-stroke compensations remain to be established. Full article

The single-leg countermovement jump (SL CMJ) is widely used to assess limb-specific neuromuscular function, with interpretation commonly centred on inter-limb asymmetry. However, contextualising unilateral performance relative to bilateral capacity remains less clearly defined. This retrospective cross-sectional study aimed to develop exploratory descriptive benchmarks for SL CMJ kinetic, kinematic, and temporal variables expressed as a percentage of bilateral CMJ performance in a heterogeneous athletic cohort. A total of 348 athletes completed bilateral and unilateral CMJs using dual force plate sampling at 1000 Hz. The best trials were selected using the modified reactive strength index (mRSI), and averaged unilateral variables were expressed relative to bilateral potential. Unilateral-to-bilateral transfer was non-uniform across metric domains. Median relative jump height and the mRSI were 44.8% and 39.4%, respectively, whereas median average relative braking and propulsive force values were 76.0% and 75.4%, respectively. Gross impulse measures were retained to a greater extent than power- and rate-dependent variables, while temporal metrics showed prolonged unilateral phase durations. Exploratory sex-based analyses indicated trivial-to-small differences in selected variables; however, these findings should be interpreted cautiously because of unequal group sizes and the descriptive nature of the dataset. These results provide broad exploratory percentile benchmarks that may help practitioners contextualise SL CMJ performance relative to bilateral execution. However, the values should not be interpreted as universal clinical thresholds, injury-risk markers, or sport-specific normative standards without consideration of sex, sport discipline, competitive level, injury history, and longitudinal athlete context. Full article

Background: Professional women’s football requires precise neuromuscular characterisation because of the high mechanical demands associated with acceleration, deceleration, jumping, braking, landing, and rapid force production. The aim was to characterise the multivariate neuromuscular profile derived from the countermovement jump (CMJ) and isometric mid-thigh pull (IMTP), and to examine neuromuscular components according to tactical positions in professional female football players. Methods: Twenty-three professional female football players were assessed using the CMJ and IMTP. Force-time, impulse, rate of force development, jump performance, landing, and inter-limb imbalance variables were extracted. Principal component analysis (PCA) was applied to the standardised variables, and individual component scores were compared according to tactical positions using one-way analysis of variance (ANOVA). Results: The first five principal components explained 79.19% of the total variance. PC1 represented the propulsive force and the rate of force development; PC2 reflected total force and mechanical impulse; PC3 represented early explosiveness; PC4 grouped indicators of inter-limb imbalance; and PC5 integrated jump performance and landing control. No statistically significant differences were observed between tactical positions. Conclusions: The combination of CMJ, IMTP, and PCA enabled multiple muscle-force variables to be synthesised into interpretable neuromuscular dimensions. The findings provide preliminary and exploratory evidence to support the individual monitoring of female football players. Given the low participant-to-variable ratio, the PCA findings should be considered exploratory. Full article

Background: Inter-limb asymmetry has been widely studied as a potential determinant of physical performance in able-bodied athletes; however, its functional relevance in athletes with neurological impairments such as spastic hemiparesis remains unclear. This study aimed to examine the associations between lower-limb isometric strength, inter-limb asymmetry, physical performance, and match external-load variables in elite CP football players. Methods: Eleven male football players with spastic hemiparesis from the Spanish national team competing at the 2024 IFCPF World Cup participated in this observational cross-sectional study. Maximal isometric strength of the plantar flexors, adductors, and hamstrings was assessed using a belt-stabilised dynamometer. Inter-limb asymmetry was calculated as a percentage difference between affected and non-affected limbs. Physical performance was evaluated using sprint, change-of-direction, dribbling, and intermittent endurance tests. Match external-load variables were collected during official competition using inertial measurement units. Associations were analysed using Spearman’s rank correlations, and between-group comparisons were conducted using a median split based on asymmetry magnitude. Results: Inter-limb asymmetry did not significantly differentiate physical performance outcomes across any field-based tests (p > 0.05). Associations between isometric strength or asymmetry and field-based performance were limited and did not remain statistically significant after false discovery rate correction. In contrast, plantar flexor asymmetry showed significant negative associations with mechanical work (ρ = −0.84; q = 0.010) and metabolic power (ρ = −0.83; q = 0.010), which remained robust after multiple-comparison control. Conclusions: Inter-limb strength asymmetry did not appear to be a primary determinant of field-based physical performance in CP football players with spastic hemiparesis. Most associations between strength, asymmetry, and performance should be considered exploratory. However, plantar flexor asymmetry showed a consistent association with selected mechanical and metabolic match-load variables, suggesting that neuromuscular asymmetry may influence specific aspects of match demands. Given the exploratory team-study design and limited sample size, these findings should be interpreted cautiously and require confirmation in larger cohorts. Full article

Background: Team sports often involve high-intensity unilateral actions that can lead to neuromuscular asymmetries, increasing injury risk and reducing performance, particularly in young female athletes. Methods: This study quantified and compared inter-limb asymmetries in single-leg countermovement jumps (slCMJ) across sexes and sports in 96 youth elite athletes (16.42 ± 1.03 years; 1.83 ± 0.09 m; 74.36 ± 8.69 kg) from basketball, handball, and volleyball. Using a force plate, asymmetries were assessed, and statistical analyses (t-test, ANOVA) identified differences. Results: Females showed greater asymmetry in jump height (9.64 ± 6.43% vs. 6.48 ± 4.87%, p = 0.01, d = 0.59), whereas males exhibited higher asymmetry in time to take-off (10.32 ± 7.5% vs. 6.4 ± 4.7%, p = 0.003, d = 0.63). Volleyball players displayed the lowest asymmetry in jump height (7.05 ± 4.9%) compared to basketball (8.73 ± 7.2%) and handball (11.88 ± 9.7%, p = 0.05), and in relative maximum power (4.63 ± 3.7%) compared to basketball (7.75 ± 5.3%, p = 0.04) and handball (6.51 ± 4.7%). Conclusions: These findings highlight sex- and sport-specific neuromuscular asymmetry patterns, emphasizing their relevance for injury prevention and performance strategies. However, asymmetries are highly variable, influenced by multiple factors. Full article

The aim of this meta-analysis was to synthesize current evidence on inter-limb asymmetries in youth athletes and to determine their magnitude, developmental determinants, and functional relevance. The review followed PRISMA 2020 guidelines, and the protocol was registered in PROSPERO. Six databases were searched from inception to October 2025. Studies assessing asymmetry as a between-limb difference in athletes aged 6–18 years were included. A total of 25 studies (N = 4125) were included qualitatively, with 24 included in the quantitative analyses. Meta-analyses were conducted for comparable outcomes (single-leg countermovement jump [SLCMJ], change of direction speed [COD], association with sprint performance, and maturation effects) using random-effects models and heterogeneity assessment (I², τ²). Mean asymmetry was 10.8% for SLCMJ (95% CI: 6.7–14.9; I² = 78%) and 7.4% for COD (95% CI: 0.5–14.2; I² = 64%). The association between asymmetry and sprint performance was small and not statistically significant (r = −0.27; 95% CI: −0.55 to 0.07). Maturation analysis showed a moderate effect (d = 0.35; 95% CI: 0.18–0.52), with peak asymmetry around peak height velocity (PHV). Heterogeneity was mainly explained by sport-specific demands and methodological differences. Asymmetries of approximately 10% are commonly observed in youth athletes in single-leg jump and change of direction tests, but their clinical relevance likely depends on sport-specific demands, maturation status, and testing modality, and should not be interpreted as a universal normative threshold. The lack of prospective injury data prevents the establishment of universal clinical thresholds. In conclusion, inter-limb asymmetries are common and developmentally dynamic in youth athletes, with functional relevance depending on biological and sport-specific context. Future research should prioritize methodological standardization and prospective designs. Full article

Limited evidence exists regarding longitudinal changes in neuromuscular function throughout a competitive season and following time-loss injuries in professional football. The aim of this study was to explore the longitudinal alterations related to time-loss injuries on surface electromyography (SEMG) and vertical jump performance in professional football players. Fourteen U-23 male professional football players were assessed at two time points during the 2019–2020 competitive season. SEMG activity of the rectus femoris, vastus medialis, vastus lateralis, biceps femoris, and semitendinosus was evaluated during the bulgarian squat (BS) and single knee straight bridge (SKSB) exercises. Vertical jump performance was assessed using squat jump (SJ) and countermovement jump (CMJ) tests performed on force platforms. Participants were classified as players experiencing time-loss injuries (IPs; n = 6) or players who remained continuously available (NIPs; n = 8) according to the occurrence of a time-loss injury (>8 days). Repeated-measures ANOVA was used to examine the effects of time point, group, limb, and exercise phase. Significant time point × group interactions were observed for CMJ inter-limb asymmetry variables, with IPs demonstrating reduced asymmetry values over time. During the SKSB exercise, biceps femoris activation was significantly lower in IPs (η²p = 0.38) compared with NIPs. No consistent alterations related to time-loss injuries were identified during the BS exercise. No consistent differences related to time-loss injuries were observed in conventional vertical jump performance measures. These observations suggest that SEMG assessment during posterior-chain exercises may provide complementary information regarding neuromuscular function in professional football players experiencing time-loss injuries beyond that obtained from conventional vertical jump assessments. Nevertheless, these observations should be interpreted with caution given the small sample size, the heterogeneous injury profile, and the exploratory nature of the present investigation. Full article

Bilateral deficit (BLD) is traditionally defined as the reduced capacity to produce force during simultaneous bilateral contractions compared with the summed output of unilateral actions. However, in applied sport settings, BLD is frequently estimated from countermovement jump (CMJ) performance, representing a functional rather than a direct mechanical measure of force production. Therefore, the aim of this study was to examine the association between a CMJ-derived functional BLD index and multidirectional performance in soccer players. Forty male university soccer players (age: 23 ± 1 years) performed unilateral and bilateral CMJ. The BLD index was calculated from jump height values obtained during these assessments. Participants subsequently completed the 505 change-of-direction (CoD) test, which was analyzed using two-dimensional video-based motion analysis. Participants were classified according to BLD magnitude into low, moderate, and high BLD groups. Group differences were assessed using Kruskal–Wallis tests with Bonferroni-adjusted post hoc comparisons. Additionally, Spearman correlation analyses were performed using BLD as a continuous variable. Significant between-group differences were observed across all temporal phases of the 505 test (p < 0.001), with players exhibiting lower BLD values demonstrating superior acceleration, deceleration, reacceleration, and overall CoD performance. Significant negative correlations were also observed between BLD and reaction time, acceleration, deceleration, reacceleration, CoD time, and CoD deficit (r_s = −0.42 to −0.69; p < 0.001). No significant associations were found for stride length, acceleration ability, or inter-limb asymmetry. These findings suggest that lower magnitudes of a CMJ-derived functional BLD index are associated with superior multidirectional performance in soccer players. However, given that BLD was estimated from jump performance, the results should be interpreted as associations with a functional neuromuscular performance index rather than as direct evidence of bilateral force production capacity. Full article

Combat sports are characterized by sport-specific asymmetrical movement patterns that may influence neuromuscular control, functional stability, and injury risk. Although lower-limb asymmetry has been widely investigated in taekwon-do experienced ITF taekwon-do practitioners, upper-limb functional symmetry remains insufficiently explored. Sixteen experienced male ITF taekwon-do practitioners underwent assessment of hand grip strength and upper-limb dynamic stability using the Upper Quarter Y-Balance Test (UQYBT). Reach distances in anterior (AP), posteromedial (PM), and posterolateral (PL) directions were analyzed together with composite symmetry indices. Inter-limb differences were evaluated using paired Student’s t-tests, and associations between strength and dynamic stability variables were examined using Pearson’s correlations. Significant inter-limb asymmetry was observed only in the posteromedial (PM) UQYBT direction, with higher values for the left upper limb (p < 0.001; dz = 1.34). No significant inter-limb differences were observed for hand grip strength, anterior reach distance, posterolateral reach distance, or composite index values. Correlation analyses demonstrated weak-to-moderate and statistically non-significant relationships between hand grip strength and dynamic stability variables. Experienced taekwon-do athletes demonstrate movement-specific upper-limb asymmetry while maintaining relatively symmetrical overall dynamic stability and grip strength. The findings further suggest that upper-limb dynamic stability may depend more strongly on neuromuscular coordination and sport-specific motor control than on maximal grip strength alone. These findings suggest that asymmetry in taekwon-do may reflect a potential sport-specific adaptation rather than generalized neuromuscular dysfunction. Full article

Background: Rifle shooting performance depends on precise postural control, rifle stability, and coordinated upper-limb force production. Although previous studies have examined postural balance and aiming stability in rifle shooters, the role of upper-limb inter-limb strength asymmetry across different shooting positions remains unclear. This study explored the association between joint-specific upper-limb strength asymmetry and rifle shooting performance in elite athletes across prone, kneeling, and standing positions. Methods: Thirteen elite rifle shooters completed a 20-shot series in each position according to ISSF rules. Bilateral maximal isokinetic strength of the wrist, elbow, and shoulder was assessed at 60°/s using a Biodex System 4 dynamometer, and handgrip strength was measured with a handheld dynamometer. Inter-limb asymmetry indices were calculated for each joint action. Position-specific shooting scores and good-10 hits (≥10.0) were recorded. Associations between asymmetry indices and performance outcomes were examined using Spearman correlation analyses and simple linear regression models. Results: In exploratory analyses, greater asymmetry in selected shoulder actions showed large negative associations with lower prone, kneeling, and standing scores, and standing performance also showed a negative association with wrist flexion asymmetry. Good-10 hits were negatively associated with selected shoulder and wrist asymmetry indices. Exploratory regression models showed large apparent proportions of explained variance for selected position-specific associations, but these estimates should be interpreted cautiously because of the small sample size and the absence of validation. Conclusions: Position-specific upper-limb strength asymmetry, particularly at the shoulder and wrist, was associated with rifle shooting performance and may represent a relevant consideration for training and monitoring in elite rifle athletes. Full article

Background: Both unilateral and asymmetric loading have been used to increase training specificity and create over-load in a target limb to reduce inter-limb asymmetries. The aim of the study was to compare the effects of conducting either unilateral- or asymmetric-loaded resistance training with traditional bilateral resistance training on maximal dynamic and isometric strength in untrained women. Methods: Thirty-four women not conducting regular resistance training were randomized into unilateral (UNI), bilateral (BIL) or asymmetric (ASY) upper-body resistance training (2–3·wk⁻¹, 10 wk, 24 sessions in total). UNI conducted all exercises unilaterally (one arm at a time), BIL conducted all exercises bilaterally (both arms), and ASY added 10% of the total load to the non-dominant side. Maximal strength was tested in chest press, seated row (1-RM and MVC in both), and pallof press (only MVC). Results: At post-test, BIL demonstrated greater bilateral 1 RM strength than ASY (p = 0.017, d = 1.25) in chest press, while UNI demonstrated greater 1 RM strength in the dominant side than ASY (p = 0.006, d = 1.45). For the other strength tests, no differences were found between groups in chest press (p = 0.068–0.481), seated row (p = 0.091–0.591) or MVC peak force for both chest press and seated row (p > 0.05). All groups demonstrated pre–post improvements for all measurements in chest press (p < 0.05) and seated row (p < 0.05), but only ASY demonstrated improvements in pallof press on the non-dominant side. Conclusions: Compared to traditional bilateral training, unilateral resistance training did not result in similar effects on dynamic or isometric strength. Asymmetric resistance training demonstrated a lower change in chest press strength on the bilateral and dominant sides compared to the other groups. Full article

Objectives: This study investigated bilateral strength asymmetry, the bilateral asymmetry index, and the bilateral deficit ratio during one-repetition maximum leg press testing performed under bilateral, unilateral, and split-load conditions and examined their associations with isokinetic knee and hip strength asymmetries. Methods: 31 resistance-trained males completed 1RM leg press tests in all loading modes, followed by isokinetic knee flexion/extension and hip extension assessments at 60°·s⁻¹. Results: The repeated measure ANOVA showed that split-load leg press had a significantly greater bilateral deficit ratio (14.29 ± 7.71%) compared to the bilateral condition (5.16 ± 9.60%, p < 0.001). Isokinetic testing showed significant inter-limb differences for knee flexion and extension but not hip extension. The bilateral strength asymmetry varied across tasks (5.17 ± 4.44% in leg press to 17.84 ± 12.40% in eccentric hip extension), while bilateral asymmetry index remained consistently lower. Bilateral strength asymmetry differed significantly across leg press conditions, whereas the bilateral asymmetry index did not. Knee flexion bilateral asymmetry index correlated with dominant and non-dominant hamstring to quadriceps ratios (respectively, r = 0.61; r = 0.37) and cross-limb flexor–extensor ratios (r = 0.42). No significant relationships were found for hip extension asymmetry. Conclusions: Split-load leg press might be used to test lower limb bilateral deficit, because it provides easily detectable deficit values. Unilateral leg press might be used to detect lateral strength differences, since it provides relation to isokinetic strength of knee flexors and extensors. Full article

There is a lack of clarity on the isokinetic testing of professional female soccer players (PFSPs) concerning the proper use of isokinetic testing, and the existing data, useful for rehabilitation purposes, are confusing. This review aims to highlight the main methodological issues and provide guidance for performing reliable isokinetic strength (IS) based on evidence data. Following the PRISMA guidelines, we selected 18 out of 98 papers dealing with healthy PFSPs surveying four databases. It emerged that there is a large difference between subjects even in comparable test conditions (e.g., usage of the same isokinetic device). The more reliable testing speed ranges from 60°/s to 180°/s. Employing lower or higher velocities does not add information to test results. Interlimb differences in healthy PFSP are confirmed to be approximately 10 percent. The H/Q ratio does not differ through the different calculation methods, considering eccentric values or not, in any considered menstrual cycle phase. It emerged that more methodological rigor is necessary in PFSP isokinetic testing. Full article