What is the absolute value of the horizontal force that each athlete exerts against the ground?

Refer to the diagram shown below.

When an athlete is in motion, he/she exerts a vertical force (the person's weight, W) on the ground. The ground exerts an equal and opposite force, N, the normal reaction on the athlete, so that W = N.

At the same time, the ground exerts a horizontal force, F, o n the athlete so that he/she does not slip.
The magnitude of the horizontal force is
F = μN = μW
where μ = the dynamic coefficient of friction.

 
The horizontal force is μW,
where
W = the weight of the athlete and,
μ = the dynamic coefficient of friction.