why do professional sprinters run with a straight back and not as streamline as possible?
In: Physics
After what’s called the drive phase (where you’re coming out of the blocks and accelerating) and you reach top speed, sustaining that speed requires you to overcome the force of gravity pushing down on you, the resulting force of friction coming into contact with the ground, and air resistance. Of these, the force of gravity pushing down is by far the most significant and is what most of the energy in a stride goes towards countering. A sprinter’s body isn’t actually perpendicular to the ground, but has about a 3° tilt forward so that when their legs hit in a line with their body, they generate enough horizontal force to overcome friction and air resistance.
If you’re asking why a sprinter’s body isn’t bent over with their legs hitting at the same angle as I mentioned, there are several reasons that sum up to it being inefficient. If your upper body is curled up to be more streamlined, you can’t breathe as well because your lungs have less space and the relaxed/weak core required to be in that position act as a shock absorber, reducing the energy return you get from a stride. Holding your body straight but perpendicular to your legs generates a moment (hold up a pencil and push up one end (the force from your legs) and the other end goes down) that you would have to overcome which uses a lot of energy.
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