From the dawn of time sprinters have been told they need to stay low during acceleration. Go to any high school or youth practice (sometimes at the college level as well) and you'll see athletes doing exactly that. They come out the blocks with their chest parallel to the ground meanwhile, their thighs and shin are perpendicular to the ground. They are "staying low" as the coach told them to do, however, this is not the desired position for acceleration; or any part of running.
Staying low is intended to allow the body to produce the horizontal forces necessary to move the body from stationary to top end speed. This should be achieved by using the whole body unit; including the shoulders, chest, hips, and legs; to push the foot into the ground in a horizontal direction opposite the direction of movement (towards the finish line). The athlete who does this best is often considered "a great starter". The thing most great starters have in common? Most don't have a break at the hip. The body stays together as one unit. This is best seen when an athlete leaves the blocks and you see a straight line from the heel through the top of the head. Most beginners don't understand this position or aren't strong enough to achieve it, so they break their hip in order to mimic it. In doing this they take impair their ability to accelerate effectively. If the chest gets too far in front of the center of mass the body has 2 options; fall, or produce vertical force to keep the athlete from kissing the track. Neither of these options yields the horizontal forces we want to get the body moving down the track.
Breaking at the hip may seem the easiest way to achieve the feeling of "staying low" however it takes impairs the bodies ability to produce horizontal force and in-turn accelerate effectively. So if you want to run fast don't break your hip.
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