There is physics in running track, especially in sprinting. Forces are acting upon the runner and they are actually more important than how fast the limbs are moving in the body when you're trying to run faster. Runners over the years have learned to use some of the forces to their advantage. One force that runners can use to their advantage is gravity. In order for gravity to help the runner, the runner must lean foward. Leaning helps gravity pull the runner foward, which causes the runner to run faster and enter the finish line quicker. Leaning also makes the work on the runner's legs easier.