Search Results (66)

Background: Isokinetic strength of the knee joint represents a significant determinant of athletic performance and injury prevention; however, its relationship with explosive performance in young female athletes remains insufficiently explored. The aim of the study was to analyze the relationships between isokinetic strength of the knee joint at different angular velocities and explosive jumping performance in young female athletes. Methods: The research sample consisted of 13 young female athletes enrolled in sport-oriented educational programs specializing in athletics. Explosive lower-limb power was assessed using performance tests for countermovement jump (CMJ), countermovement jump free arms (CMJ FAs) and squat jump (SJ) administered with the Chronojump system. Isokinetic strength of the knee flexors and extensors was assessed using the Humac Norm dynamometer in the concentric mode at angular velocities of 60°/s, 180°/s, and 300°/s. Peak torque, the ipsilateral H:Q ratio, and bilateral asymmetries were evaluated. Pearson’s correlation coefficient was used to analyze the relationships between the investigated parameters. Results: The strongest relationships with explosive performance were observed for hamstring strength at an angular velocity of 180°/s, where significant high correlations were identified with performance in the CMJ (r = 0.693), CMJ FA (r = 0.754), and SJ (r = 0.713). In contrast, quadriceps strength demonstrated predominantly low to moderate associations with jumping performance, while no significant correlations were confirmed at an angular velocity of 300°/s. Bilateral asymmetries of the knee extensors and flexors were generally low, ranging approximately between 7 and 10%, whereas the values of the ipsilateral H:Q ratio were within the physiological range of approximately 50–55%. Conclusions: The results suggest that the ability to generate force at higher contraction velocities, particularly in the hamstrings, is significantly associated with explosive performance in young female athletes. At the same time, isokinetic strength assessment appears to be an appropriate tool for evaluating muscular strength, muscle balance, and potential asymmetries in youth sports. However, explosive performance cannot be explained solely by the level of maximal muscular strength, but rather by a complex interaction of neuromuscular and biomechanical factors. 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

Objective: The primary aim of this study was to compare eccentric knee flexion isokinetic performance at two commonly used angular velocities (60°·s⁻¹ and 180°·s⁻¹) between dominant and non-dominant limbs in healthy professional soccer players through the analysis of peak torque, mean peak torque, angle of peak torque, total work, and rate-of-torque-development-related variables. The secondary aim was to describe concentric knee extension and knee flexion strength variables assessed at 60°·s⁻¹. Methods: Forty male professional soccer players performed concentric knee flexion–extension testing at 60°·s⁻¹ and eccentric knee flexion testing at 60°·s⁻¹ and 180°·s⁻¹ using an isokinetic dynamometer. Peak torque (PT), mean peak torque (MPT), angle of peak torque (APT), total work (TW), and hamstrings: quadriceps ratios (H:Q ratios) were analyzed for dominant and non-dominant limbs. Inter-limb differences, repetition effects, and reliability indices were calculated. Results: No significant inter-limb differences were observed for most variables (trivial–small effect sizes), except for higher eccentric TW at 180°·s⁻¹ in the dominant limb (p = 0.009). Eccentric PT and MPT decreased at higher velocities in both dominant (p = 0.002 and p < 0.001, respectively) and non-dominant (p = 0.008 and p < 0.001, respectively) limbs, while APT shifted toward more flexed knee angles (p < 0.001). Reliability was good to excellent (ICC = 0.81–0.87), with low measurement error. Conclusion: Eccentric knee flexion assessment at 60°·s⁻¹ and 180°·s⁻¹ angular velocities provided different results in PT, MPT, and APT for the same group of players, supporting the use of more than one eccentric test for obtaining information about these variables in elite soccer. Full article

Hamstrings–quadriceps (H–Q) imbalance represents a biomechanical marker of knee instability and injury risk in running. This in silico (simulation-based) study introduces a digital machine learning framework designed to estimate H–Q imbalance using biomechanical features derived entirely from synthetic running trials and conceptually mappable to inertial-sensor domains. Key biomechanical predictors included the dynamic hamstrings-to-quadriceps ratio (H:Qdyn), the knee moment limb symmetry index (LSI), and the early-stance co-contraction index (CCI), all standard indicators of muscular balance and coordination in sports medicine. A reduced musculoskeletal framework emulating flexor–extensor balance, limb symmetry, and co-contraction patterns generated 573 synthetic running trials for 160 virtual subjects across three speeds. These interpretable features trained a calibrated gradient-boosting classifier evaluated via ROC-AUC, PR-AUC, balanced accuracy, F1, and Brier score. Across all conditions, the model achieved ROC-AUC 0.933 (95% CI 0.908–0.958), balanced accuracy 0.943 (95% CI 0.924–0.962), PR-AUC 0.918 (95% CI 0.892–0.943), F1 0.940 (95% CI 0.919–0.958), and Brier 0.056 (95% CI 0.041–0.072), outperforming the logistic baseline. Dynamic H:Q ratio and knee moment symmetry were the dominant predictors, while co-contraction provided complementary biomechanical nuance. These results demonstrate that simulation-derived frameworks can reproduce IMU-relevant biomechanical variability, enabling interpretable machine learning for transparent assessment of muscular balance in sports medicine. Full article

Background: Combining body composition, dynamic postural control, and isokinetic strength allows for a comprehensive physical and functional assessment of football players across specific playing positions. The aim of this study was to analyze the field position-related variations in the physical and functional profiles of male football players. Methods: A convenience sample of 23 professional male football players from a Portuguese second league team, aged 18 to 32 years (23.83 ± 3.77 years), participated in the present study. Players from five field positions (central backs, central midfielders, wide midfielders, and forwards) were assessed for body composition, dynamic postural control, and isokinetic lower limb strength. Body composition was assessed by bioelectrical impedance; composite scores for postural control in the right and left limbs were obtained through the Y-Balance test lower quarter (YBT-LQ). Peak torque (PT) during lower limb flexion and extension was measured using an isokinetic dynamometer chair. Results: Significant differences were found only in peak torque of the right extensors [H (4) = 9.84, p = 0.043, η² = 0.37)], whereas no significant differences emerged in body mass, dynamic balance scores, left-side extension and flexion, or hamstring-to-quadriceps (H:Q) strength ratios. Post hoc analysis using Mann–Whitney U tests with Holm correction did not confirm pairwise differences between positions. The correlation analysis revealed mainly moderate-to-strong associations between symmetrical measures (composite YBT-LQ right and left, PT extension right and left), as well as between anthropometric and strength variables, but without consistent position-specific patterns. Conclusions: Overall, the study provides valuable insights into the physical attributes of professional football players, highlighting the general similarity of profiles across positions and suggesting that individualized training approaches may still be beneficial to optimizing performance and reduce injury risk. Future studies should extend the analysis to larger cohorts across different professional Portuguese football teams and competitions. Full article

Background: Sarcopenia, characterized by loss of muscle mass, strength, and function, reduces independence and quality of life in older adults. Strength exercise (STR) mitigates these age-related declines, but evidence of short-term effectiveness remains limited. This study aimed to evaluate the effects of eight weeks of STR on body composition, muscle strength, and psycho-emotional state in community-dwelling elderly women. Methods: A prospective, controlled, non-randomized study included 44 women assigned to an STR (n = 20) or control (CON, n = 22) group. The STR group performed supervised exercise twice weekly for eight weeks. The outcomes were body composition, handgrip strength (HGS), quadriceps (Q) and hamstrings (H) strength, and perceived stress (PSS-10), assessed at baseline and after intervention. Within-group changes were analyzed using paired t-tests, and between-group differences were evaluated using analysis of covariance (ANCOVA) adjusted for baseline values. Results: After baseline adjustment, body mass (p = 0.041, partial η² = 0.103), BMI (body mass index, p = 0.030, partial η² = 0.115), and body fat percentage (p = 0.047, partial η² = 0.098) were significantly reduced in the STR group. Significant improvements were observed for H strength in both legs (p < 0.05, partial η² = 0.128–0.131), right HGS (p = 0.025, partial η² = 0.122), right HGS:BMI ratio (p = 0.013, partial η² = 0.150), and H:Q ratios on both sides (p < 0.05, partial η² = 0.109–0.118). No significant differences were observed for left-hand grip strength, knee extensor strength, or other body composition variables (p > 0.05). The perceived stress scores were significantly lower in the STR group post-intervention (p = 0.036, partial η² = 0.108). Conclusions: An eight-week supervised strength exercise program was associated with favorable changes in muscle strength, body composition, and psycho-emotional state in elderly women. Full article

This study compared the body composition and strength of the lower extremity parameters between novice runners (NRs) and amateur marathon runners (AMRs). A total of 50 NRs (33.84 ± 4.32 years) and 50 AMRs (33.36 ± 5.55 years) were analyzed cross-sectionally. Bioelectrical impedance analysis measured body composition parameters, and isokinetic testing assessed knee muscle strength. The results showed that compared to AMRs, NRs had lower fat-free mass (FFM), skeletal muscle mass (SMM), and total body water (TBW) (−15, −12, and −5%; all p < 0.01) but higher body fat percentage (PBF) and visceral fat area (VFA) (+27 and +32%; both p < 0.01). They also had 6% lower knee extensor (KE) strength and 31% lower knee flexor (KF) strength on the dominant legs (DLs) and 14% lower KF strength on the non-dominant legs (NDLs). In addition, their hamstring–quadriceps ratio (H: Q) was 24% lower on the DLs and 9% lower on the NDLs. The NRs exhibited significant negative correlations between PBF, VFA, and knee muscle strength (r = −0.54 to −0.42, p < 0.01), while the AMRs had significant negative correlations only for PBF (r = −0.59 to −0.57, p < 0.001). In conclusion, the NRs exhibited lower FFM and TBW, higher PBF and VFA, and reduced muscle strength. In contrast, the AMRs exhibited the opposite pattern. These findings suggest that NRs with elevated body fat (BF) indicators should prioritize fat reduction and performance enhancement, while those with lower muscle mass require targeted programs to increase muscle capacity and joint stability. This approach may advance them toward the level of AMRs. Future studies should adopt longitudinal designs to explore how training interventions influence the physiological adaptations observed in runners at different experience levels. Full article

Introduction: Women’s futsal demands strength, agility, speed, and endurance, involving sprints, dribbling, and rapid directional changes. In this context, the hamstring/quadriceps (H/Q) strength ratio and bilateral muscle asymmetries are recognized as risk factors for lower limb injuries and may also impact athletic performance. Objective: This study aimed to analyze power output in two inertial flywheel resistance exercises and identify muscle imbalances in the lower limbs of female university futsal players. Methods: Twelve athletes (22.9 ± 2.3 years; 163 ± 6.8 cm; 60.9 ± 9.9 kg; 22.8 ± 3.1 kg/m²; ≥9 years of experience) participated in the study. They performed 2 sets of 8 unilateral knee flexion and extension repetitions per limb, following a warm-up of 20 bodyweight squats. Power output was assessed using a multi-joint isoinertial device (Physical Solutions, SP, Brazil). Data were analyzed using mean and standard deviation, with significance set at α = 0.05. Results: Eccentric power was significantly higher in both exercises and limbs (EJPD = 0.003; EJPE = 0.006; FJPD < 0.001; FJPE < 0.001). An imbalance in the H/Q ratio was observed: concentric right = 50.38% ± 14.67; left = 42.46% ± 9.24; eccentric right = 56.71% ± 15.56; left = 58.38% ± 21.06. The right limb showed a greater concentric imbalance (p = 0.016). Conclusions: Eccentric power was higher in both exercises without inter-limb differences. An H/Q imbalance was detected, with greater asymmetry in the right leg for concentric power. Coaches are encouraged to prioritize eccentric training to address these imbalances. Full article

Studying normative values for muscle activation in the vastus lateralis (VL), vastus medialis (VM), and biceps femoris (BF), as well as the hamstrings/quadriceps (H:Q) ratio during the Countermovement Jump (CMJ). Determine whether there were differences between the CMJ and the trial of 5 consecutive CMJs (5 CMJ) and between the take-off and landing phases. A cross-sectional descriptive study. Thirty-one participants (20 females and 11 males, 22.52 ± 3.295 years, BMI 24.32, weight 58.23 ± 4.32 Surface electromyography has been used to determine muscle activation during the CMJ and 5 CMJ. Muscle activation in the VL, VM, and BF, as well as the hamstrings/quadriceps ratio in take-off and landing phases of the CMJ and 5 CMJ. The results show normative values in the VL, VM, and BF during both the CMJ and 5 CMJ, with the exception of the BF during the landing phase of the 5 CMJ. In conclusion, the activation in the take-off phase of the VM and VL is greater than during the landing phase. The BF shows similar activation in both the take-off and landing phases. The 5 CMJ does not induce greater muscular fatigue than the CMJ. Full article

Background/Objectives: Power indices may provide valuable information for performance and injury prevention in soccer players, so increasing the knowledge about them seems essential. Therefore, this study aimed to establish limb-specific normative values for flywheel-derived power indices in professional soccer players, while accounting for limb performance or ability, to explore the relationships between power indices across variables and to compare the power outcomes related to these indices between injured and non-injured players within four months post-assessment. Methods: Twenty-two male professional soccer players (age: 26.6 ± 4.6 years; competitive level: Belgian second division) were recruited from a single elite-tier club to participate in this cross-sectional diagnostic study. Participants underwent a standardized assessment protocol, executed in a rotational inertial device, comprising six unilateral exercises focused on the lower limbs: hip-dominant quadriceps (Qhip), knee-dominant quadriceps (Qknee), hip-dominant hamstrings (Hhip), knee-dominant hamstrings (Hknee), adductor (Add), and abductor (Abd). The testing session incorporated a randomized, counterbalanced design, with each exercise comprising two sets of eight maximal concentric–eccentric repetitions per limb. Leg dominance was operationally defined as the self-reported preferred limb for ball-striking tasks. Power indices were calculated from these exercises. Results: No significant differences in flywheel-derived power indices were found between limbs or between injured and non-injured players. However, significant correlations between indices were found in all power variables, with the Qhip:Qknee and Hhip:Hknee concentric ratios emerging as the most clinically actionable biomarkers for rapid screening. Conclusions: These results suggest the necessity of including more variables for injury prediction. Moreover, power indices could be considered based on the classification of limbs as “strong” or “weak”. Full article

Background: Anterior cruciate ligament (ACL) injury is more prevalent in young athletes and women. A deficit of knee flexor strength and a H/Q strength ratio below 0.6 in athletes are risk factors. Therefore, the main objective of this study is to determine if there are differences in the strength of the knee musculature, joint work, and H/Q ratio between professional and junior elite basketball players and sexes, since there are differences in the incidence of ACL injuries between these groups. Methods: Forty-three professional (27 male and 16 female) and 42 junior elite (28 male and 14 female) basketball players were evaluated. Dynamometric knee flexion and extension measurements were performed on both lower limbs at three angular velocities: 30°/s, 120°/s, and 180°/s. Concentric knee flexion and extension strength variables were measured in Newtons, the strength ratio between flexors and extensors in H/Q ratio, and muscle work (product of force times displacement) in Joules. Comparisons of the measured variables were made between categories and sexes. Results: Significant differences (p < 0.05) were found between categories (professional and junior) in all measured strength parameters as well as in joint work. No differences were found between categories in the H/Q ratios. Significant differences (p < 0.05) were found between sexes in most measured strengths and joint work. However, no differences were found in most of the H/Q ratios. Female basketball players have lower values of strength and muscle work than male players, however, in the H/Q ratio data there are no differences between the two groups. The same occurs between junior and professional athletes. Conclusions: The authors conclude that flexor and extensor strength values should be analyzed in isolation and not in terms of the H/Q ratio. Full article

Background and Objectives: A prominent area of research in adolescent ACL reconstruction (ACLR) involves graft selection, with particular interest in the quadriceps tendon (QT) as an alternative to hamstring tendon (HT) autografts, although comparative studies on muscle strength outcomes and patient satisfaction in adolescents remain limited. This study aims to evaluate the influence of QT and HT autografts on muscle strength and satisfaction outcomes post-ACLR in adolescents. Methods: This prospective study was conducted at the Lithuanian University of Health Sciences, enrolling 68 patients aged 12–17. ACLRs were performed using QT or HT autografts. Muscle strength was assessed using an isokinetic dynamometer (Biodex), while patient satisfaction was evaluated through IKDC, Lysholm, and ACL-RSI surveys preoperatively and 12 months postoperatively. Results: 54 patients (24 QT and 30 HT) completed the study. The data are non-parametric and are presented as median (IQR). Isokinetic measurements indicated that QT harvesting led to significantly lower extension strength compared to HT 6 months (p = 0.019) and 12 months post-op (p < 0.001) but showed better H/Q ratios 6 months (p = 0.019) and 12 months post-op (p < 0.001). There was no significant difference between the QT and HT groups in ACL-RSI and Lysholm scores. IKDC scores were significantly higher in the HT group (p = 0.009). Conclusions: QT autografts provide favorable H/Q ratios, yet they exhibit weaker extension strength and lower satisfaction outcomes compared to HT. These results suggest a need for individualized rehabilitation protocols and further research to optimize ACLR graft selection for adolescents. Full article

Purpose: Anterior cruciate ligament reconstruction (ACLR) using the hamstring graft is commonly performed to restore knee stability; however, it induces significant neuromuscular and biomechanical changes, particularly in the hamstring. This study aimed to evaluate the changes in maximum effective angle, hamstring strength, and hamstring-to-quadriceps (H/Q) strength ratio at 3 and 6 months post-ACLR and compare these outcomes to a control group. Methods: This prospective controlled study included 20 ACLR patients and 20 age- and gender-matched controls. Hamstring peak torque, maximum effective angle (MEA), and the H/Q ratio were assessed using isokinetic dynamometry at 60°/s. The ACLR group was evaluated postoperatively at 3 and 6 months, while the control group underwent a single evaluation. Results: At 3 and 6 months, the ACLR group exhibited significantly lower MEA (26.3° ± 8.2 and 28.2° ± 9.4) compared to the control group (36.4° ± 12.0; p < 0.01). Hamstring peak torque and H/Q ratios were also lower in the ACLR group but showed slight improvements over time. The H/Q ratio increased significantly between 3 and 6 months (51% to 56%; p = 0.041). Conclusion: The use of hamstring graft in ACLR leads to persistent MEA and strength deficits despite rehabilitation. Advanced, targeted rehabilitation protocols are essential to address these deficits, optimize recovery, and reduce the risk of reinjury. Full article

Some knee strength measuring devices have an anterior cushioning area but relies on a belt for the posterior pad adjustment, creating an uneven force distribution. This study analyzed whether the distal pad position affects knee strength measurements. Eleven professional basketball players participated in this study, with a total of 22 knees evaluated. Knee flexion and extension dynamometric measurements were performed at different angular velocities: 30°/s, 120°/s, and 240°/s. For each angular velocity, two measurements were performed with varying positions of the measuring tool pad at the anterior and posterior aspects (AA and PA). The hamstring/quadriceps (H/Q) ratio was calculated by dividing the hamstring musculature’s maximum peak strength by the quadricep musculature’s maximum peak strength at each measurement. The knee work was extracted from the device after finishing the measurements. Significant differences were found between measurement positions in the knee flexion force at 30°/s (p < 0.001) and 120°/s (p = 0.027). No differences were found for the extension forces. As for the H/Q ratio, significant differences were found between positions at 30°/s (p < 0.001). Furthermore, significant differences between positions were found for the knee work at 120°/s (p = 0.019). These findings suggest that the positioning of the pad on the leg directly influences knee flexor strength measurements, which in turn impacts critical parameters, such as the H/Q ratio and knee work. Given the importance of these variables in injury prevention, particularly for conditions such as anterior cruciate ligament (ACL) injuries, ensuring precise and reliable measurement methods is essential. We recommend using the PA position because it increases knee flexion strength values, potentially leading to more accurate assessments of the muscle function and balance. Full article