The first step is won forward, not upward
On an instrumented treadmill and then over 100 meters, what separates runners is not the total amount of force applied to the ground, it is the share of that force directed forward. The ratio of forces correlated with performance, the total force did not. Two players who push equally hard do not accelerate the same way if one pushes down and the other pushes ahead.
Morin, Edouard, Samozino, 2011, Medicine and Science in Sports and Exercise 43(9), 1680-1688