Background: Soccer is the most widely practiced sport in the world, demanding high-speed activities such as jumps, sprints and changes of direction. Therefore, having optimal levels of muscle strength improves performance and reduces the injury rate. Objectives: The objectives of our study were (i) to determine the dynamometric profile of hip muscle strength in young soccer players by position, evaluated at different isokinetic speeds, (ii) to describe the conventional and functional unilateral muscle strength ratios, (iii) to analyze the bilateral balance. Methods: Thirty-seven male soccer players (age 17.02 ± 0.92 years) participated in the study. Strength assessment was performed with a functional electromechanical dynamometer, and concentric and eccentric strength of abductors, adductors, extensors and hip flexors were measured bilaterally at 0.5 m/s and 1 m/s. Results: For eccentric right hip abduction at 0.5 m/s, defenders are significantly stronger than midfielders (p = 0.013) and stronger than forwards (p = 0.140). For eccentric right hip adduction at 0.5 m/s, defenders are significantly stronger than midfielders (p = 0.005) and stronger than forwards (p = 0.253), as for eccentric right hip adduction at 1 m/s, defenders are significantly stronger than midfielders (p = 0.014) and stronger than forwards (p = 0.084). There is a significant effect for the conventional strength ratio of left abduction/adduction at 1 m/s. The conventional strength ratio of forwards is significantly higher than that of defenders (p = 0.045) and higher than that of midfielders (p = 0.152). Conclusions: Concentric and eccentric hip strength values differ according to playing position.

Change of directions (COD) involves multidirectional and complex actions, with performance influenced by multiple factors. As lower limb strength is one of the most determinant of COD performance, the present study aimed to (a) explore the differences in strength outcomes across different lower limb muscle actions between faster and slower basketball players in COD actions at different angles and (b) analyse the relationship between isometric, concentric and eccentric strength outcomes and COD performance at different cutting angles. Twenty‐five basketball players (44% female) completed a battery of tests, encompassing isokinetic and isometric squat strength assessments, along with COD tests at 45°, 90° and 180°. Players were categorised as ‘low‐performance’ and ‘high‐performance’ groups based on execution time in COD, facilitating a comparison between performance groups. Results indicated that concentric strength showed the greatest differences between performance groups at 45° COD (effect size ≥ 0.813; p ≤ 0.034). Isometric and eccentric strength demonstrated a moderate‐to‐large relationship with 90° COD performance (Rho ≥ 0.394; p ≤ 0.045), and all muscle actions exhibited a large relationship with 180° COD (Rho ≥ 0.445; p ≤ 0.030). Moreover, the fastest players showed higher levels of concentric strength relative to eccentric strength, regardless of the cutting angle. These findings hold practical applications, suggesting that basketball coaches should train a specific kind of muscle action depending on the individual players' COD demands, focusing on improving the rapid eccentric force application while striving to reduce the eccentric/concentric ratio.

Background: In soccer, the repeated execution of unilateral actions may lead to uneven limb development, promoting the occurrence of asymmetries. However, there is no consensus on the impact of these asymmetries on sports performance or the influence of playing position on their magnitude. Methods: A cross-sectional study was conducted with 33 male federated soccer players (age: 18.42 ± 4.24 years; body mass: 70.23 ± 8.74 kg; height: 1.76 ± 0.07 m; body mass index: 22.6 ± 2.7 kg/m²). Hamstring strength asymmetry between the dominant and non-dominant limbs was assessed using functional electromechanical dynamometer (FEMD) at eccentric velocities of 0.4, 0.8, and 1.2 m/s. Physical performance was evaluated through a 30 m sprint and countermovement jump (CMJ). Differences according to playing position were also analyzed. Results: Significant between-limb differences were found in strength, power, and impulse, with effect sizes increasing as testing velocity rose. No significant differences in asymmetry levels were observed across playing positions, and no correlations were found between hamstring asymmetry and physical performance outcomes. Conclusions: Although functional lower-limb asymmetries were identified in soccer players, these asymmetries did not directly influence performance nor vary across playing positions. The findings suggest that certain asymmetries may represent normal functional adaptations in soccer rather than pathological structural imbalances.

The aim of this review was to evaluate the impact of strength training on hamstring muscle strength and physical performance in football players. A systematic review was conducted following the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines, and the protocol was registered in PROSPERO. A literature search was performed using four electronic databases, such as Web of Science, SCOPUS, SportDiscuss, and PubMed. Randomized controlled trials conducted with football players aged 15 years or older were included. The studies were grouped according to moderating variables such as training protocol and physical performance outcomes. A total of 20 studies met the inclusion criteria for this review, with 10 studies included in the meta-analysis. Strength training programs demonstrated moderate to large effects on both concentric and eccentric strength of the hamstrings and quadriceps, as well as on physical performance measures such as jumping and sprinting. Eccentric overload training produced the most significant benefits in sprint and jump performance. Strength training, particularly eccentric training, significantly improves both the hamstring muscle strength and the physical performance in male football players aged 15 years and older, highlighting its importance for injury prevention and sport performance enhancement. However, additional research is needed to evaluate whether similar benefits can be observed in female players and younger age groups.