# Effects of different heavy sled loads sprint training on acceleration performance in adolescent sprinters

## TL;DR

This study shows that heavy sled training improves adolescent sprinters' acceleration and sprint performance, with different loads affecting specific aspects of their running mechanics.

## Contribution

The study provides novel insights into optimal sled loads for improving acceleration and kinematics in adolescent sprinters.

## Key findings

- Heavier sled loads (40% and 50% body mass) improved 30m sprint times and kinematic parameters like trunk angle and step length.
- Lighter sled loads (25% body mass) enhanced 60m sprint performance but not as effectively as heavier loads for acceleration.
- Training with 40% and 50% body mass sleds led to greater improvements in sprint kinematics compared to non-resisted training.

## Abstract

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.

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).

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).

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.

The online version contains supplementary material available at 10.1186/s13102-025-01370-5.