Anyone involved in sports has probably seen athletes sprinting while pulling a weighted sled behind them. It makes sense, strengthening your body to run faster in a very specific manner. But then the debate begins about how weight is too much. You see, less weight mimics the direct act of natural, unweighted sprinting, while more weight gives a greater stimulus for strength gains. After using our force plate with athletes and seeing sprint times measured on a daily basis, we started to reevaluate this process of resisted running and its relation to TIME spent on the ground.
Previously (see SpartaPoint 11/3/10), we discussed how longer toes are advantageous for sprinters because it allows a longer time to apply force into the ground, a biomechanical variable known as impulse. We simplify the term impulse, referring to it as TIME, describing an athlete’s ability to create force over a longer duration. This TIME helps a sprinter by increasing their opportunity to propel themselves forward in the desired direction.
A 2010 study out of the Humboldt University in Berlin, Germany found that faster accelerations, the ability to go from standing to sprinting, were generated in athletes with greater propulsive forces, or larger TIME performances. This strategy allows a lower, more forward oriented body postures. Makes sense as running is often described as an exercise where you are falling and recovering without actually appearing that way.
One of the best ways to force more TIME on the ground, and the resultant lower body lean is providing the athlete with more resistance. However, it becomes difficult to judge how much weight to use, so we got back to basics and our coaches manually resist each athlete, forcing them to really push into us, rather than trying to pull something behind them. However if you’re intent on using sleds, it seems that to spend more TIME on the ground, a heavier weight would be your best option and to save the technique work for actually sprinting. Joe DeFranco, another great strength coach in the field, really loads up to the sleds and has athletes lean and drag the resistance across the room.
The problem seems to arise when we live in that gray area, using a smaller weight for resisted running to focus on technique, but it could never be as good as unweighted, natural sprinting. Unfortunately, this lighter weight is probably not enough to stimulate more TIME on the ground.
So load up that resistance, whether it is a sled or manual from a coach. The other option is to just sprint without any resistance for sheer technique focus. Your results will always seem to be clearer in black and white.