The topic of resisted sprint training for the purposes of enhancing sprint speed continues to be a hot topic in strength and conditioning circles. A widely accepted general rule has been to avoid resisted loads of greater than 10% body weight. Heavier loads may alter sprint mechanics and result in less dynamic correspondence to non-resisted runs. However, more data is starting to emerge that challenges this widely accepted “rule”. Some coaches like heavier sled towing drills to develop greater horizontal force production and hip extension strength. However, much of the positive benefits of heavy sled towing on acceleration and sprinting are mostly anecdotal.
A new paper ahead of print in the Journal of Strength and Conditioning Research compared the effects of different sled towing loads on sprinting speed in a group of collegiate male Sports Science students. The subjects were divided into three training groups; a low load group (5% of body mass, n=7) a moderate load group (12.5% of body mass, n=6) and a high load group (20% of body mass, n=6). For seven weeks, each group performed 2 workouts per week for a total of 14 workouts. Each session involved the same volume and distribution of work and differed only by resisted sprint load. The training sessions involved between 4-8 repetition of 20-35 meter sprints at maximal intensity with the prescribed load. Total distance covered per week ranged between 250-370 meters. Rest periods of 3-5 minutes were given between attempts and workouts were performed after at least 48 hours rest. 40 meter sprint times were assessed before and after the 7-week training intervention.
The results showed the that heavy loads group improved 0-20 and 0-40 meter sprint time. The low and moderate load groups improved their times between 10-40 (low load), 20-30 and 20-40 (moderate load) but neither improved in 0-10, 0-20 or 0-30 meter.
The researchers advise that coaches seeking to improve sprint performance within the acceleration phase (e.g., 0-30 meters) may want to use heavier resistive loads (20% body mass) whereas coaches seeking to improve the fly phase of the sprint should consider using lower to moderate resistive loads (5-12.5% body mass).
Though this paper supports the usefulness of heavier loads for resisted sprinting, it is still unclear if even heavier loads (<bodyweight) provide any benefit or detriment to sprint or acceleration performance. Though the research is assessing loads greater than 10%, these loads are still quite conservative compared to what many coaches are using in the field. It’s not uncommon to see coaches load stacks of 45 lb weight on to sleds for their athletes. Time will tell if these much heavier loads are worth using in training. However, it is becoming a little more clearer that heavier loads (20% body mass) may enhance acceleration.
Bachero-Mena, B., & González-Badillo, J. J. (2014). Effects of resisted sprint training on acceleration with three different loads accounting for 5%, 12.5% and 20% of body mass. The Journal of Strength & Conditioning Research. Ahead of Print