Myth: The key to running faster is moving your limbs faster. QUICKER STEPS & FASTER ARMS = GREATER SPEED.
The limiting factor in acceleration and top speed is usually not how fast an athlete can drive their knee or cycle their arms, but rather how much FORCE they can apply to the ground in the appropriate direction and within the appropriate time.
For example, when we coach an athlete to improve their acceleration phase they are surprised to learn that in acceleration, the ground is your friend. You need to apply as much force as possible, as long as possible in order to accelerate at the greatest rate. The change in velocity is related to the force applied in the opposite direction multiplied times the amount of time that force is applied to the ground. As soon as the athlete removes their drive leg foot from the ground, they are no longer accelerating until the swing leg foot makes contact with the ground on the next step. Maintaining ground contact through an explosive, forceful and complete triple extension push will yield the greatest increase in velocity. The knee drive will set up their next powerful, triple extension push.
Athletes should be coached in the acceleration phase to MAXIMIZE their push and therefore their ground contact time yielding a greater increase in velocity.