Optimizing Load Parameters for Resisted Sled Sprint Training on Artificial Turf through Biomechanical and Kinematic Analysis in Soccer Players

Background: Resisted Sled Sprint (RSS) training is widely used to enhance sprinting speed across various sports by applying external loads to stimulate the lower limbs. This study investigates the optimal load for RSS by examining biomechanical and kinematic responses in soccer players to different load levels, focusing on how external loads affect sprint velocity and performance dynamics. Methods: Twenty-nine soccer players participated in a controlled experiment involving five 20-meter sprints under varying load conditions Results: A linear regression showed a significant relationship between load and sprint velocity decrease (%Body mass = 1.222 × %V_dec + 5.8, R² = 0.612). Increased loads led to reduced stride length and sprint speed but enhanced contact time, propulsive duration, vertical impulse, and ankle dorsiflexion. Notably, the 10%V_dec condition significantly increased propulsion impulse. Conclusions: On artificial turf, external load strongly correlates with reduced sprint velocity in 20m resisted sled sprints. Higher loads improve ankle dorsiflexion and trunk tilt, facilitating horizontal force during acceleration. Although a 10% speed reduction minimally affects stride length and joint angles, it significantly boosts horizontal extensor force in soccer players.