The New York Times created a Wonderful Graphic to describe what was happening during the 100m final. Unfortunately they got some of the comments wrong.
This article from Wall Street Journal describes the process very well and shows acceleration up to 50m and deceleration after 70m.
NYT: His reaction times are often slowThe reaction times of Bolt and Gatlin was 0.155 vs 0.153, so the initial difference isn't due to the reaction time is due to their initial stride pattern and body angle. Taller athletes are at a disadvantage remember Carl Lewis?
NYT: Bolt usually gets to full speed (about 12 meters a second) at the 60-meter mark. By then, Gatlin’s lead had evaporated.Usain Bolt probably reached a higher top speed by about 50-70m accounting for closing the gap.
NYT: Bolt owns this part of the race for a simple reason: He creates more force into the ground in less time than anyone else.This description is probably valid for 40-60m. After 60-70m it is all about who is decelerating the least.
Usain Bolt takes fewer strides overall and conserves his energy much better.
Even when he relaxes, looks left, smiles at Justin Gatlin and taps his chest he is still not decelerating as much as anyone else.
This man is so fast he has enough time to stop and cheese for the camera before crossing the finish line. #Bolt pic.twitter.com/UOxZzAQWR3
— John Haltiwanger (@jchaltiwanger) August 15, 2016