This is my attempt to summarize the essence of sprinting. Nothing complicated, just the basics. No need to complicate.
Let’s start with a generic definition of speed. According to the Premier Global NASM, speed is the ability to move the body, or parts of the body through the largest range of motion in the least amount of time.
The purpose of the start is to overcome inertia to put the body in optimum posture to accelerate to top speed or, if change of direction is required, to optimum speed.
The bottom line is to be able to effectively get the body into postures that allow for maximum force production into the ground in the least amount of time. A long body line aligned through the hips with the head still and neutral is the desirable posture.
In acceleration as the body advances forward the initial foot contact is behind the C of G and over the first steps the point of foot contact moves under the body. I think of it in the following pattern: PUSH/PUSH/PUSH/HIPS TALL
Cyclic action of legs ? Step over ankle (Steps one, two & three), Step over Calf (Steps four five and six), Step over knee ( All subsequent steps)
The arms play a big role in sprinting. At the start to help impart force back against the blocks and to maintain balance. As the sprint progresses the arms serve a balance function and secondary function to help with force production.
Relaxation is a key to sprinting. Undue tension is detrimental. Running fast demands constant cycling of tension and relaxation.
The legs cross each other in a reciprocal scissors action with the free (Swing Leg) foot crossing above the knee with each step.
Step down from above. The closer the landing foot lands under C of G the better.