Though good running form is useful in increasing speed, fast and slow runners have been shown to move their legs at nearly the same rate – it is the force exerted by the leg on the ground that separates fast sprinters from slow.[3] Top short-distance runners exert as much as four times their body weight in pressure on the running surface. For this reason, muscle mass in the legs, relative to total body weight, is a key factor in maximizing footspeed.[3]