Sprint-resisted training involves towing a sled of a given load for the purposes of developing increased force production and stride length. Sprint-assisted training involves the athlete receiving assistance during the sprint, enabling a greater stride rate and higher velocity than can be performed without the assistance. The optimal load for sprint-resisted training has been debated for years among coaches and scientists. For a long time, it was believed that towing a load greater than 10% of the athletes’ body mass would alter sprint mechanics and thus result in undesirable adaptations. In recent years, some coaches have been experimenting with heavier towing loads with anecdotes of successful performance outcomes. Research investigating how very heavy versus traditional sled loads impact sprint performance is required to guide best training practices.
A new study published ahead of print in the International Journal of Sports Physiology and Performance evaluated the effects of very heavy sled towing on horizontal force production. A sample of 16 amateur male soccer players were divided into a heavy sled group (80% of body mass) versus a control group (sprint training without resistance). For a period of 8 weeks, each group performed workouts twice per week comprised of 10 sets of 20 m sprints. Mechanical outputs (e.g., horizontal force production) and sprint performance across 5 and 20 m were evaluated before and after the 8-week training program.
The results showed that maximal horizontal force production increased substantially more in the very heavy sled group (Effect Size, ES = 0.80) versus the control group (ES = 0.20), though the between group difference was deemed unclear. In addition, overall more force was applied horizontally for the very heavy sled group than the control group after training with a moderate between-group difference. Improvements in 5 and 20 m sprint times were deemed moderate and small for the very heavy sled group and small and trivial for the control group respectively. Thus, it appears that sprint resisted training with a load at 80% of body mass can be quite useful for improving very short distance acceleration. This can be an effective modality particularly for team sport athletes who frequently accelerate but rarely reach maximum velocity as a result of frequent changes of direction.
Reference: Morin, JB. et al. (2016) Very-Heavy Sled Training for Improving Horizontal Force Output in Soccer Players. International Journal of Sports Physiology and Performance. In press.