Context: Manipulation of resistance training variables influences the structural and functional adaptations of muscle, having a great impact on sport performance and hamstring injury prevention. Objective: To analyze how the main resistance training variables affect the biceps femoris long head architecture in soccer players. Data Sources: Five databases were searched from inception to January 2024. Study Selection: Studies that included training intervention groups and measured muscle architecture adaptations before and after the training program in soccer players were included. Study Design: Systematic review with meta-analysis. Level of Evidence: Level 2. Data Extraction: Muscle thickness, fascicle length, and pennation angle were extracted from included studies as main outcomes. Results: Six studies and 12 training groups (168 participants) were analyzed. The effects of Nordic hamstring exercise (NHE) against soccer interventions, volume of training, and frequency of training as independent variables were analyzed. NHE significantly improved biceps femoris long head fascicle length (P = 0.01). Training twice a week did not show significant differences compared with training once a week. Higher volumes of training (ie, >290 repetitions) in a period of 6 to 12 weeks with 57 repetitions per week demonstrated significant effects. Conclusion: NHE lengthens the fascicle, especially if a sufficient volume (ie, >290 repetitions) and 2 days per week are performed. It is still unknown how the programming of some fundamental variables such as intensity, degree of effort, or exercise selection affects the muscle architecture of the biceps femoris long head.
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