I found an article on this so just wanted to share the info.
With Usain Bolt, he has
Drive Phase
7 steps for his acceleration, shin angle on his 7th step foot strike is perpendicular to ground, torso remains slightly inclined,
Transition Phase
he has 10 steps for this phase, on the 10th step his torso will be somewhat at 90deg now he is coming into his
Max Velocity Phase
after another 10 steps or so he will have reached his maximum speed at about 60m, then
Speed Maintenance Phase
for the rest of the 100m, 14 steps remaining.