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M45 British Record holder Jason Carty (11.01sec) sled pulling
Weighted sleds and acceleration
As with the theme of posts recently I'm looking at adding some different aspects to my coaching sessions this winter... evolution rather than revolution and resisted sled pulls/pushes is something that I'm keen on. I dug out some old articles I'd written and this snippet seems to have some relevance to directing my thoughts.
Athletes from numerous sports tow weighted sleds (or car tyres) loaded with weights over distances – usually 5m-40m - to improve their acceleration. Variations in standing start are used, for example, three point, standing and sprint starts. It's also possible to push using devices such as prowlers.
Achieving a low driving position is particularly important if the athlete is to get in the best position to overcome inertia. The added load will force the athlete to drive hard through their legs and pump vigorously with their arms.
A team of Greek researchers looked specifically at the validity of towing methods as a way of improving both acceleration and sprint speed *. Eleven students trained using 5kg weighted sleds (the RS group) and eleven without (the US group). Both followed sprint-training programmes, which consisted of 4x20m and 4x50m maximal effort runs. These were performed three times a week for 8 weeks. Before and after the training programs the subjects performed a 50-metre sprint test. The students’ running velocity was measured over 0-20m, 20-40m, 20-50m and 40-50m. In addition stride length and stride frequency were evaluated at the third stride in acceleration and between 42-47m during the maximum speed phase.
The researchers discovered that the RS group improved their running velocity over the 0m– 20m phase ie their acceleration improved. However, this acceleration improvement had no effect on their flat out speed. This contrasted with the US group who improved their running velocity over the 20-40 m, 40-50m, and 20-50 m run sections. This led the researchers to draw the obvious conclusions that, “Sprint training with a 5kg sled for eight weeks improved acceleration, but un-resisted sprint training improved performance in the maximum speed phase of non-elite athletes. It appears that each phase of sprint run demands a specific training approach.”
* J Sports Med Phys Fitness. 2005 Sep;45(3):284-90.
However, if sleds are used as a means of improving acceleration, what is the optimum load to tow for maximum training adaptation? Australian researchers from Sydney considered just this *. Twenty male field sports players completed a series of sprints without resistance and with loads equating to 12.6 and 32.2% of body mass. The team discovered that stride length was significantly reduced by approximately 10% and 24% for each load respectively. Stride frequency also decreased, but not to the same extent as stride length. In addition sled towing increased ground contact time, trunk lean, and hip flexion. Upper body results showed an increase in shoulder range of motion with added resistance. Crucially it was discovered that the heavier load generally resulted in a greater disruption to normal sprinting technique compared with the lighter load. In short towing heavier weight sleds in unlikely to specifically benefit acceleration.
I'll add a little to this... the base level of power of the sprinter will have an effect... more powerful athletes will be able to generate greater force and this should also be factored into consideration when loading sleds. Many coaches time the acceleration too, and this will provide an objective measurement as to whether the land is too much or too little. Note: I believe that too much will be much more disruptive than too little... we are after speed, frequency, stride-length and optimum technique - factors which are less likely to be disrupted by "lighter" loads.