Effects of forward, backward, and combined resisted sprint training on sprint performance, sprint kinematics, and isokinetic knee muscle function in recreational soccer players

This study aimed to compare the effects of forward, backward, and combined (i.e., forward and backward exercises) resisted sprint training on sprint performance, sprint kinematics, and isokinetic knee muscle function in recreational soccer players. Thirty-six recreational male soccer players were randomly assigned to forward, backward, or combined resisted sprint training and completed a 6-week intervention (two sessions per week) using sled resistance corresponding to 20–55% of body mass. Sprint performance (5–20 m), spatiotemporal and kinematic sprint variables, and isokinetic knee muscle strength and power were assessed before and after training. Sprint performance over 5 m, 10 m, and 20 m improved significantly following the intervention (p < 0.001), with no significant time × group interactions. Trunk angle exhibited a significant time × group interaction (p < 0.05), with reductions observed in the forward and combined training groups only. No significant changes were observed in stride length or stride frequency. Knee muscle eccentric strength and concentric power increased significantly across all groups (p < 0.001), with comparable adaptation magnitudes. Forward, backward, and combined resisted sprint training effectively improved sprint performance and knee muscle function in recreational soccer players. Direction-specific trunk angle adaptations indicate distinct kinematic responses to different training modalities, supporting the potential use of combined resisted sprint training as a practical training option. Practically, resisted sprint training using light-to-moderate external loads appears effective for improving short-distance sprint performance and knee muscle function in amateur soccer players.