Front Side vs Back Side Mechanics: What makes Better Sprinters
When it comes to separating the elite sprinters from just the pretty good sprinters, there's a whole heap of factors at play, but for me, there are two that stand out.
The first is ground contact time. Elite sprinters spend less time on the ground, with both top speed and acceleration.
Sprinting is often described as controlled falling, or a series of horizontal jumps one after another, at top speed the goal is to maximise flight time and horizontal distance with each stride while minimising inefficiencies such as braking forces. During acceleration, athletes spend longer on the ground (compared with top speed) because they have to break inertia and create more force. That doesn't mean you should try to spend as long as possible on the ground, elite sprinters still have shorter contact times than slower humans during acceleration.
In both acceleration and top speed, elite sprinters have a much shorter ground contact time than non-elite runners. Bolt's longer contact time at top speed is made up for his longer stride length (Bolt covers 110m in 41 strides, while Gay takes 44).
But the other big factor is better sprinters have more front side dominant mechanics when it comes to leg recovery.
Sprinting can be broken down into front side mechanics; everything that happens as you bring the leg forward preparing to strike the ground. And backside mechanics; everything where we're pushing the leg back into the ground and creating triple-extension.
The two are very much connected. If you get a better rearward elbow drive, you will achieve a much better contralateral (opposite side) knee drive. If we consider what science is showing us, knee drive or front side mechanics seems to be more highly correlated to sprinting speed than backside, which initially might seem counterintuitive because of how much we talk about the importance of glutes are when it comes to creating power.
Knee drive and powerful front side mechanics wind up your legs like a spring preparing them to explode into the ground. If you can't coil that spring tight initially, the glutes aren't able to do their work.
The gait cycle is broken down into a whole bunch of phases. The recovery phase is when you bring the leg back after toe-off and hip extension. Recovery can go wrong in two ways. First, it can stay behind the centerline of the body, meaning you waste time as you have to bring it back into that knee-driven position for your next stride, or it can recover in front of the body but in a weak and a low position. This means you haven't coiled the spring that is your leg tight enough to allow the glutes to do their work.
When coaching our athletes, we have what's called a lead domino technique effect. Get that first technical factor right, and everything else will follow. When it comes to sprinting the three lead dominos are: Mid-foot strike under the body, a powerful arm action, and appropriate* knee drive. Get them right everything else will follow.
*Appropriate is almost always more, but you can still go too far
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