Search Results (770)

The purpose of this study was to examine associations between lower-limb mechanical strength, phase-oriented composite strength indices, generalized neuromuscular activation, and maximal soccer ball kicking speed in trained athletes. Twenty-five male soccer players (age: 20.64 ± 2.50 years; height: 179.28 ± 4.27 cm; body mass: 75.80 ± 9.41 kg) participated in this cross-sectional study. Isometric ankle and knee joint torques were assessed using an isokinetic dynamometer, and joint-specific and phase-oriented cross-joint composite indices were computed to represent integrated strength capacity across the kinetic chain. Neuromuscular activation was evaluated via surface electromyography during a standardized squat jump task. Ball-kicking speed was measured using Doppler radar during maximal instep kicks. Associations were analyzed using Pearson correlation coefficients (p ≤ 0.05) with false discovery rate correction for multiple comparisons. In unadjusted analyses, moderate positive correlations were observed for several ankle torque variables and composite ankle strength indices, while swing-phase composite measures demonstrated moderate correlations (r = 0.43–0.55). Knee strength indices and sEMG variables showed no significant relationships. However, none of the variables remained statistically significant after FDR correction, suggesting limited independent explanatory value of isolated isometric strength and non-task-specific neuromuscular activation assessed during a standardized squat jump for maximal kicking performance. Full article

Lower-limb strength is a health and performance indicator in adolescents, although its assessment often fails to account for the influence of sex and biological development. This study aimed to analyze the associations between anthropometric parameters, maturational status, and physical activity levels with jumping performance in adolescents. A cross-sectional study was conducted with male and female adolescents (mean age: 13.60 ± 1.50 years). Anthropometric variables, maturational status, and physical activity levels were assessed. Performance was measured using the Countermovement Jump (CMJ) and Standing Broad Jump (SBJ). In males, jumping performance was significantly associated with height (p = 0.002), lower-limb length (p < 0.001), and muscle mass (p < 0.001). However, fat mass emerged as a substantial factor, exhibiting a large effect size on performance (p < 0.001). Maturational status in males showed significant differences, with late maturers performing lower than on-time and early maturers (p < 0.023). In females, structural anthropometry and maturation showed limited-to-no significant associations with performance, except for a negative association with fat mass (p < 0.035) and a positive association between muscle mass and CMJ (p < 0.020). Active adolescents of both sexes performed significantly better than inactive ones in both CMJ and SBJ (p < 0.011). In conclusion, jumping performance in adolescents is characterized by marked sexual dimorphism. In males, greater height, lower-limb length, lower fat mass, and early maturation are positively associated with superior performance. Conversely, in females, these factors exhibit limited influence on jump outcomes. Full article

This study investigated interlimb asymmetries in lower limb performance using both vertical and horizontal jump tests in elite young basketball players. Specifically, it aimed to determine whether (1) unilateral jump performance and (2) the magnitude of interlimb asymmetry differed across maturity groups, whether (3) limb dominance influences performance, and whether (4) asymmetry direction is consistent across tests. One hundred elite male basketball players (U13 to U19) were categorised into three maturational stages: Pre-PHV (n = 19), Circa-PHV (n = 29), and Post-PHV (n = 52). Each athlete performed the following unilateral tests with both the dominant and non-dominant leg: single-leg hop, triple hop for distance, 6 m timed hop, single-leg countermovement jump (SL-CMJ), and single-leg drop jump (SL-DJ) from a 30 cm box. The Bilateral Strength Asymmetry (BSA) index was computed for each test. All tests showed significant differences between Pre-PHV and Circa-PHV groups (p < 0.001), whereas only the 6 m timed hop differed between Circa-PHV and Post-PHV (p < 0.01). BSA did not differ significantly across maturation stages in any test, except for the single-leg hop. Agreement in asymmetry direction between test pairs was slight to fair (kappa ≤ 0.29). BSA values remained largely stable across maturational stages, suggesting that interlimb asymmetries are established before PHV, likely during childhood. Limb dominance did not affect jump performance, and asymmetry direction varied between tests, confirming they are not interchangeable. Full article

Background: Upper limb functional performance depends on the interaction of strength, mobility, and neuromuscular control, while inter-limb asymmetries may increase injury risk. However, comprehensive analyses integrating these factors remain limited. This study aimed to evaluate sex differences and identify functional phenotypes in young adults using a multidimensional assessment approach. Methods: Forty-six healthy young adults (23 women, 23 men) underwent a comprehensive battery of upper limb assessments, including anthropometric measurements, maximal handgrip strength, isometric elbow flexion and extension torque, postural stability via the Fall Risk Index (FRI), and functional reach using the Upper Quarter Y-Balance Test (YBT-UQ). Inter-limb symmetry was calculated using the Limb Symmetry Index (LSI). K-means clustering was applied to standardized variables to identify latent functional phenotypes. Results: Men demonstrated significantly greater body mass, height, limb length, and absolute strength (p < 0.01), while functional performance (YBT-UQ composite scores) and inter-limb symmetry were similar between sexes. Strength asymmetry was most prevalent for elbow flexion and handgrip strength (up to 89%), whereas stability asymmetry was less frequent (≈54%). Three functional clusters were identified: Cluster 1—high strength and moderate stability, Cluster 2—lower anthropometry and strength, Cluster 3—high strength but reduced stability and increased asymmetry. Despite phenotypic differences, composite functional performance was comparable across clusters. Conclusions: Upper limb function reflects the interaction of morphological and neuromuscular factors rather than strength alone. Observed asymmetries should be interpreted within a functional context, as moderate asymmetries may represent normal variation in motor control, while larger asymmetries may indicate potential functional imbalance; however, due to the cross-sectional design of this study, no causal inferences regarding injury risk can be made. Functional phenotyping provides a framework for individualized training, screening, and rehabilitation strategies. Full article

Background/Objectives: Knee joint instability is frequently reported in individuals with knee osteoarthritis (OA) and may persist after total knee replacement (TKR), where it represents a leading cause of revision. However, neuromuscular factors associated with knee instability remain poorly understood. This systematic review and meta-analysis aimed to compare neuromuscular characteristics between individuals with stable and unstable knees in OA and TKR populations. Methods: PubMed, CENTRAL, Scopus, and EMBASE were searched from inception to 10 January 2025. Studies comparing neuromuscular outcomes between stable and unstable knees were included. Neuromuscular parameters included: muscle strength, muscle power, muscle activation pattern, and joint stiffness. Where appropriate, pooled standardized mean differences (SMD) were calculated using random-effects models. Certainty of evidence was evaluated using the GRADE approach. Results: Nineteen studies (16 OA, 3 TKR; n = 7369 participants) were included, with eleven studies eligible for meta-analysis. OA individuals with unstable knees demonstrated significantly lower limb muscle strength compared with stable counterparts (SMD = −0.49, 95% CI −0.81 to −0.16, p = 0.003). Muscle co-contraction did not differ significantly between groups (SMD = 0.12, 95% CI −0.70 to 0.94, p = 0.77). The overall certainty of evidence was rated as very low. Conclusions: Knee instability in OA populations is associated with reduced lower limb muscle strength, although evidence quality is limited and findings regarding neuromuscular control strategies remain inconclusive. Evidence in TKR populations is scarce. Future studies should investigate muscle activation patterns and dynamic joint stabilization during functional tasks to clarify the neuromuscular mechanisms underlying knee instability. Full article

Background: Tibial pilon fractures are complex injuries frequently associated with persistent functional impairment, even after successful surgical fixation. While previous studies have reported deficits in muscle strength and balance, little is known about the side-to-side variations in intrinsic biomechanical and viscoelastic muscle properties following surgery. Objectives: This study aimed to compare the biomechanical and viscoelastic properties of ankle periarticular muscles between the affected and non-affected limbs in patients with surgically treated unilateral tibial pilon fractures. A secondary objective was to evaluate the relationship between intrinsic muscle properties and isometric muscle force. Methods: A total of 39 subjects with unilateral surgically treated tibial pilon fractures were evaluated after fracture healing. Myotonometric assessment was performed to evaluate muscle mechanical parameters, including tone (frequency), stiffness, and elasticity (decrement), as well as viscoelastic properties, including relaxation time and creep, in the tibialis anterior, peroneus longus, medial gastrocnemius, and lateral gastrocnemius muscles. Isometric muscle force of ankle dorsiflexors and plantar flexors was measured using a handheld dynamometer. Side-to-side comparisons and Pearson correlation analyses were performed. Results: The affected limb showed significantly reduced ankle range of motion in all planes and significantly lower isometric muscle force in both the dorsiflexors (p = 0.0002) and the plantar flexors (p = 0.0066). Stiffness was significantly higher in the medial (p = 0.038) and lateral gastrocnemius (p = 0.045) muscles on the affected side. Decrement was significantly increased (indicating reduced elasticity) in the peroneus longus (p = 0.021). No significant differences were observed for tone, relaxation time, or creep. Conclusions: Myotonometry revealed increased stiffness in the gastrocnemius muscles and reduced elasticity in the peroneus longus on the operated side compared with the non-affected limb. Tone and viscoelastic properties did not differ significantly between sides. However, tone, stiffness, and elasticity were significantly correlated with muscle force, indicating a relationship between intrinsic muscle mechanical properties and force production after tibial pilon fracture surgery. Full article

This study develops a reduced-order predictive model of the Sit-To-Stand (STS) task to examine whether a simplified biomechanical representation can reproduce key STS patterns reported in the literature and to investigate the role played in movement by a flexible trunk. The model represents the human body as a planar multibody system and formulates STS as an optimization problem within a discrete mechanics framework. This formulation combines reduced model complexity, explicit torso flexibility, and a structure-preserving numerical approach for trajectory generation. Simulations were used to evaluate the effects of movement duration, reduced joint strength, and seat height on joint torques, kinematics, trunk motion, and ground reaction forces (GRFs). The results reproduced several qualitative trends reported in previous experimental studies, including increased peak joint torques and GRFs with shorter movement duration, lower joint strength, and reduced seat height, as well as greater compensatory trunk motion under more demanding conditions. These findings suggest that the proposed framework captures key adaptive features of STS mechanics and may provide useful insights for rehabilitation analysis and the design of assistive technologies such as lower-limb exoskeletons and rehabilitation devices. At the same time, the present work should be regarded as an initial methodological study, since validation is currently qualitative and further experimental calibration, quantitative validation, and sensitivity analysis remain part of ongoing work. Full article

Inter-limb asymmetries are common in soccer players and are frequently monitored in high-performance settings; however, their expression across different flywheel-based strength exercises, movement phases, and over time remains unclear. This study aimed to (i) compare inter-limb power asymmetry magnitudes across multiple unilateral flywheel exercises and between concentric (CON) and eccentric (ECC) phases, and (ii) describe changes in these asymmetries over an 8-week period of routine soccer training, stratified by baseline asymmetry magnitude. The present study was designed as an observational and descriptive study. Twenty-one professional male soccer players completed two testing sessions separated by eight weeks. Players performed six unilateral flywheel exercises targeting hip- and knee-dominant quadriceps (Qhip, Qknee), hip- and knee-dominant hamstrings (Hhip, Hknee), adductors (ADD), and abductors (ABD). For each exercise and limb, the repetition with the highest CON mean power and its consecutive ECC phase were selected for analysis. Inter-limb asymmetry (%) was calculated for mean and peak power in both phases. Across exercises, ECC asymmetries were generally greater than CON asymmetries, with the largest values observed for Qknee peak power (CON: 12.86 ± 11.04%; ECC: 27.60 ± 13.65%) and Hknee peak power (CON: 10.45 ± 11.26%; ECC: 24.01 ± 20.46%). Exercise-specific patterns were evident, with generally weak associations between asymmetries across tasks. Over time, players classified with higher baseline asymmetry (≥10%) presented lower values at follow-up in several outcomes (particularly ECC-related measures), whereas players with lower baseline asymmetry (<10%) showed small increases or remained stable; These between-group patterns should be interpreted cautiously, as they may be more strongly influenced by regression to the mean and measurement variability than by underlying physiological changes. Overall, inter-limb power asymmetries assessed with flywheel technology were phase- and exercise-specific in this professional soccer sample. These descriptive findings may help contextualize phase-specific and multi-exercise asymmetry monitoring in professional soccer settings. Full article

Optimizing neuromuscular strength and balance is essential for performance and injury prevention in elite Paralympic sport. However, limited evidence describes how these parameters change over time during specific phases of the training season in athletes with lower limb deficiencies. This retrospective case series aimed to describe longitudinal changes in neuromuscular and balance performance during the fundamental preparation period in elite athletes using prosthetic devices. Routinely collected performance data from five international-level Paralympic athletes (Para-swimming and Para-athletics) were retrospectively analyzed across two preparatory observation windows conducted in consecutive competitive seasons. Neuromuscular performance was assessed using countermovement jump variables, while static balance was evaluated through Inertial Measurement Unit-derived sway metrics. Within-athlete changes were examined using descriptive and exploratory analyses. At the group level, changes were observed in selected neuromuscular and balance outcomes over time, including jump height and path length. Individual analyses revealed substantial inter-athlete variability in the magnitude and direction of changes across all outcomes. Overall, the findings indicate that neuromuscular and postural performance may fluctuate meaningfully during preparatory phases in elite athletes with lower limb deficiencies. This study provides exploratory insights derived from real-world training settings and highlights the value of longitudinal monitoring to support individualized performance management in Paralympic sport. Full article

Background/Objectives: Biomechanical research in surfing provides important insights into performance optimization and injury prevention, but the evidence remains fragmented across multiple domains. Methods: This scoping review aimed to systematically organize the existing literature on surfing biomechanics and evaluate the quality of the included studies. Searches were conducted by two independent reviewers in PubMed, Scopus, and Web of Science in accordance with the PRISMA Extension for Scoping Reviews. Systematic searches were performed up to 31 July 2025 using Boolean operators guided by the PECO framework. Methodological quality was assessed using the Downs and Black Quality Assessment Checklist. Results: Of the 195 records identified, 53 duplicates were removed. Following screening and fulltext review, 26 studies were included. Five studies employed randomized controlled designs, while 21 were non-randomized. Publications ranged from 2010 to 2025, with the majority conducted in Australia (65.4%). A total of 490 healthy surfers (mean age: 22.9 ± 16.1 years) were analyzed, with sample sizes ranging from 6 to 42 participants. Research topics included anthropometry, paddling biomechanics, aerial maneuvers, core and trunk strength and mobility, lower-limb function, frontside bottom turns, and pop-up performance. The studies’ methodological quality score was 11.7 points with substantial inter-reviewer agreement (κ = 0.77). Research on surf biomechanics remains limited in volume and exhibits methodological heterogeneity. Conclusions: Although existing studies provide valuable insights into key performance actions, further high-quality and standardized research on performance phases (e.g., paddling, pop-up, turns, aerials) and with different research designs (e.g., longitudinal, sex inclusive, ecological designs integrating lab and in-water measures) is needed. Full article

Background/Objectives: Restoring lower-limb strength and symmetry is crucial after ACL injury and reconstruction. The limb symmetry index (LSI) is often used to assess strength symmetry for return-to-sport decisions, but various assessment methods can influence outcomes. This study aimed to compare LSI across common knee flexor testing methods in healthy male athletes and to examine associations between absolute strength outcomes, thereby establishing baseline reference values for LSI in a healthy population. Methods: Twenty-two healthy recreationally active males participated in this prospective cross-sectional study. Knee flexor strength was assessed bilaterally using three force plate isometric tests, a static dynamometer-based test (isometric), and isokinetic dynamometer-based tests. Absolute strength values were normalized to body mass. LSI values were calculated for each testing condition. Differences in LSI across modalities were analyzed with repeated-measures ANOVA, and associations between normalized strength outcomes were assessed using Pearson correlation coefficients. Results: LSI values ranged from 96.69 to 101.83 across the testing conditions, with no significant differences observed between measures. Normalized absolute strength outcomes demonstrated very strong correlations within the same measurement category (r = 0.86–0.94 for force plate tests and r = 0.88–0.96 for isokinetic tests). In contrast, correlations between isometric and isokinetic strength outcomes were moderate (r = 0.41–0.67). Conclusions: LSI values were consistent across knee flexor strength testing modalities, suggesting that symmetry assessment was relatively consistent across different measurement methods in the studied group. In contrast, normalized absolute strength outcomes showed only moderate and variable associations across modalities, indicating that different testing approaches assess related but not interchangeable aspects of muscle strength. Full article

Background: This study examined the associations between dynamic maximum strength (front squat [FS] and clean [CL]), lower-limb vertical force–velocity (F–V) profile characteristics, and both absolute and scaled measures of competitive weightlifting performance in trained weightlifters. Methods: Fourteen competitive male weightlifters (age: 27.6 ± 4.2 years; height: 1.74 ± 0.05 m; body mass: 85.1 ± 6.7 kg; body fat: 11.7 ± 2.8%) completed three testing sessions separated by 48–72 h, including 1-RM assessment in the FS and CL, as well as vertical countermovement jump trials to determine individual force–velocity profile parameters (F₀, V₀, and Pmax). Official competition results obtained within the same competitive season were recorded for the snatch (SN), clean and jerk (C&J), total (TOT), and Sinclair score. Participants were additionally divided into higher and moderate jump performance groups using a median split of unloaded countermovement jump height. Results: Very strong correlations were found between 1-RM strength (FS and CL) and weightlifting performance, with CL showing the strongest associations with SN (r = 0.82), C&J (r = 0.93), and TOT (r = 0.94). Among F–V parameters, V₀ and Pmax were significantly associated with competitive outcomes (r = 0.63–0.70), whereas F₀ was not. V₀ was significantly associated with SN (r = 0.69), C&J (r = 0.63), and TOT (r = 0.70), while F₀ showed trivial-to-small associations (r = 0.08–0.28). When participants were divided using a median split of CMJ height, higher jumpers exhibited greater V₀ (3.02 ± 0.30 vs. 2.61 ± 0.23 m·s⁻¹, p = 0.014, g = 1.4) and relative Pmax (32.44 ± 2.65 vs. 27.28 ± 1.06 W·kg⁻¹, p = 0.001, g = 2.4), despite similar F₀ (p = 0.67). Higher jumpers also demonstrated superior SN (p = 0.016, g = 1.4), C&J (p = 0.041, g = 1.1), TOT (p = 0.018, g = 1.4), and Sinclair scores (p = 0.001, g = 2.1). Conclusions: In trained weightlifters, performance was strongly associated with maximal strength, while velocity- and power-oriented characteristics (V₀ and Pmax) were also associated with performance outcomes. In contrast, F₀ showed no meaningful associations with performance within this sample. These findings suggest that, among already strength-trained athletes, the ability to express force at higher contraction velocities may be associated with differences in competitive performance. Full article

High-intensity interval training (HIIT) has emerged as a time-efficient exercise strategy with potential benefits for older adults. However, evidence regarding its effects on functional fitness, body composition, and quality of life in older women remains limited. This randomized controlled trial included community-dwelling older women allocated to a HIIT group or a control group. The intervention consisted of a 65-week HIIT program (3 sessions/week), while the control group maintained usual activities. Functional fitness was assessed using standardized field-based tests, body composition was evaluated by bioelectrical impedance analysis, and quality of life was measured using the WHOQOL-BREF questionnaire. Pre- and post-intervention assessments were performed under standardized conditions. Data were analyzed using mixed ANOVA models, with significance set at p < 0.05. Compared with the control group, the HIIT group significantly improved aerobic capacity (2MST: +25.4 vs. −19.6 repetitions; p < 0.001), lower-limb strength (30s CST: +4.8 vs. −2.6 repetitions; p < 0.001), and mobility (TUG: −0.3 vs. +0.4 s; p < 0.001). Body composition improved with reductions in body fat percentage (−1.8% vs. +1.9%; p < 0.001) and visceral fat index (−0.6 vs. +0.3; p < 0.001), alongside increased total body water (+2.3% vs. −1.8%; p < 0.001). Quality of life improved significantly in physical, psychological, and environmental domains (p < 0.001). HIIT was associated with improvements in functional fitness, body composition, and quality of life, with no major adverse events reported. These findings support the use of HIIT as a practical intervention to enhance health and functional independence in aging populations. Full article

Background: The back squat is a key strength and conditioning exercise used to develop lower-limb strength and power, yet little is known about how movement velocity influences its acute performance-enhancing effects, such as improvements in countermovement jump height and power. The present study examined the acute effects of slow (v_slow) versus fast (v_fast) eccentric-phase velocity during back squats performed withmaximal concentric velocity on subsequent countermovement jump (CMJ) performance, using a randomized, crossover design. Methods: Fourteen male subjects (age = 22.9 ± 1.9 years; height = 1.8 ± 0.1 m; mass = 76.4 ± 8.3 kg) visited the laboratory on two separate days and completed a comprehensive task-specific warm-up followed by three v_slow or v_fast back squats at 70% of one-repetition maximum. Three CMJs were performed before and 30 s, 4 min, 8 min, and 12 min after the interventions. Jump height, peak power, kinetic energy, maximum knee angle, and knee angular velocities in both eccentric (downward) and concentric (upward) phases were recorded. Results: No significant (p > 0.05) between-condition differences were detected in any measure. Compared to pre-intervention, significant increases (collapsed data) were detected in jump height (6.0%; d = 0.68–0.83), power (3.6–6%; r = 0.32–0.38), and kinetic energy (5.0–8.0%; d = 0.62–0.86) at 30 s and 4 min. Conclusions: Given the lack of between-condition differences, the eccentric movement velocity of moderate conditioning back squats with maximal concentric velocity exercises does not appear to influence subsequent jump performance enhancements. Thus, either conditioning activity can be used to improve subsequent jump performance. However, as performance was enhanced only at 30 s and 4 min post-intervention, the window of opportunity is narrow, and timing should be carefully considered when including such activities in pre-competition routines. Full article

(1) Background: Postoperative anterior cruciate ligament reconstruction often involves quadriceps strength asymmetry, leading to abnormal lower limb biomechanics during running. While previous studies have examined the relationship between isokinetic strength and walking or jumping, the association between running, a key criterion for return to sport, and lower limb biomechanics remains unclear, particularly regarding isokinetic strength asymmetry at different angular velocities. (2) Methods: Isokinetic quadriceps strength, running kinematic, and kinetic data were collected from 39 ACLR individuals. Paired t-tests compared bilateral differences, and Pearson correlation analysis assessed associations between biomechanical parameters and muscle strength. (3) Results: The injured leg showed significantly weaker Qc at 60°/s, 180°/s, and 300°/s (p < 0.05). Compared to the uninjured leg, the injured leg demonstrated a significantly greater hip flexion angle at initial contact (p < 0.05); the injured leg exhibited significantly reduced knee flexion angle at the time of peak vertical ground reaction force and peak knee flexion angle (p < 0.05); the injured leg exhibited significantly reduced knee flexion moment at PVGRF, peak knee flexion moment, peak knee extension moment (p < 0.05). Both the 60°/s Qc and Qe showed moderate negative correlations with knee flexion angles, and 180°/s Qc correlated with knee flexion moment at PVGRF (p < 0.05). (4) Conclusions: ACLR patients show quadriceps strength asymmetry and abnormal sagittal knee and hip biomechanics during running. Strength symmetry moderately correlates with knee kinematics and kinetics in a velocity-dependent manner. Rehabilitation should focus on multi-speed and eccentric training with neuromuscular and hip–knee coordination exercises to optimize movement and support safe return to sports. Full article