Resisted sprinting is an effective training modality for improving acceleration speed. A common way of adding resistance to a sprint is to have the athlete tow a weighted sled while they accelerate. However, there is great debate over optimal levels of resistance. A commonly used rule of thumb has been to avoid using loads in excess of 10% of the athlete’s bodyweight, or to not allow a greater than 10% reduction in speed. The purpose being that proper sprint mechanics will break down with greater loads and thus result in less transfer to actual sprinting.
Just recently, a paper was published in the Journal of Strength and Conditioning research that investigated the effects of high verses low load sled towing. Kawamori and his team of researchers (2013) split 21 physically active men into 2 groups. Group 1 trained with loads that reduced sprint velocity by 10% while Group 2 trained with loads that reduced sprint velocity by 30%. The intervention period consisted of 2 sessions per week for 8 weeks. Pre and post 10m sprint times were collected in all subjects. Group 2 saw greater improvements in acceleration times compared to Group 1.
The results of this study suggest that heavier towing loads can in fact result in improved acceleration ability. However, it must be kept in mind that these subjects were not advanced athletes. More research is needed in trained, high level athletes to determine its effectiveness for this population. However, the idea that athletes should stick to the “10% rule” when performing resisted sprints requires careful reconsideration.
Kawamori N, Newton RU, Hori N, Nosaka K. (2013) Effects of weighted sled towing with heavy versus light load on sprint acceleration ability. J Str Cond Res, doi: 10.1519/JSC.0b013e3182915ed4