You should think of the leg as passing underneath you as fast as possible horizontally. Here the hip extensors will be producing as great a force as possible. The knee extensors and plantar flexors will be producing necessary force to keep you vertical. The foot should still be in dorsi flexion to prevent force being lost at the ankle ie. on the ball of the foot but heel very close to ground.
After the leg has passed behind the COM, the knee extensors and the plantar flexors are activated more to propel the body horizontally and vertically.
All these actions have to be learned first, but are ideally not forced ie. reflex.
START
On the video powell land with low plantar flexion, the feet are almost in neutral position (he makes contact with all the foot except the heel).
For Powell the push phase is in linear line (hips extension with feet landing in line with is hips)
Gay land more on toes, particularly in the first few steps out of the blocks where he land on his big toes. He also have slight side to side legs push (mostly like hips extension + hips abduction)
Start ground contact times
Gay:0.16s
Powell:0.19s
6 first steps GCT addition
Gay:0.86s
Powell:0.99s
TOP SPEED
Top speed reach
Gay: 70m
Powell: 60m
Strides per seconds
Gay: 4.90
Powell: 4.96
Strides length
Gay: 2.42m
Powell: 2.6m
Powell is faster than Gay in the video, only Gay is wearing spikes, Powell have flats.
On top speed motion, their foot mechanics looks almost the same the feet are almost in neutral position
All this foot mechanic seem very confusing. My coach is from the HSI school telling me that I should run almost on my toes TO REACH HIGHER HEIGHT. Contrary to the post opinion, this doesn’t seem to increase GCT, quite the contrary. HSI (to my limiting knowledge) seem to also be very strong on high leg frequency.