Background Sled sprint training to improve athletes` sprint performance is becoming increasingly popular. However, there is still no consensus on the appropriate resistance to improve acceleration, and few studies have focused on adolescent sprinters. This study aimed to investigate the effects of 8 weeks of different heavy-load sled sprint training on acceleration performance and kinematics in adolescent sprinters. Methods Thirty-two adolescent sprinters were assigned to four groups: three resisted groups (25%, 40%, and 50% body mass [BM]; n = 8 each) and one non-resisted group (NRS; n = 8). Participants trained twice weekly for 8 weeks. Pre- and post-training assessments included 30 m and 60 m sprint performance and kinematic parameters (step length, step frequency, contact time, flight time, trunk angle, push-off angle, shin angle, and hip angular velocity). Results For sprint performance, within-group improvements were significant in 30 m for 40% and 50% BM groups and in 60 m for 25% BM group (p < 0.05). Between-group comparisons showed greater 30 m improvements in 40% and 50% BM groups compared to NRS group (p < 0.05). In terms of sprint kinematics, within-group improvements were significant for step length (0-30 m) and step frequency (10-20 m) across all resisted groups, and for trunk angle (toe-off) (0-20 m) and push-off angle (10-20 m) in the 40% and 50% BM groups. Between-group comparisons showed significantly greater trunk angle (10-20 m) in 40% and 50% BM groups compared to NRS group (p < 0.05). Conclusions These results indicate that heavier sled training (40% and 50% BM) was more effective in enhancing speed, trunk angle, and step length in acceleration, whereas lighter sled training (25% BM) benefited 60 m sprint performance. This study highlights how different training loads impact sprint performance, providing coaches with insights into kinematic changes following prolonged training and aiding in the optimization of sprint training programs for adolescents.
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