When I work with young athletes to help them with their sprinting, I like to use “before/after” videos to show their improvements. So I video them before “coaching” cues, then video them after my coaching.
In the top video (prior to coaching), the athlete is sprinting on his heels. This is very common in young athletes. I tell them, “You’re foot is going “kerplunk” every time it hits the ground!” His foot is actually hitting the ground twice.
In the bottom video, the athlete is sprinting on the ball of his feet. Much better form! This was after heavy sled marching…then light sled running. Using the sled helps to create muscle memory….to “store” good form. (BTW, the athlete had to put on a hoodie toward the end of our session as it got colder!)