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