Here's a youtube video I found of Tyson Gay:
http://www.youtube.com/watch?v=ujEjRy-u0YwHe runs with a kind of side to side motion in his upper body. Usain Bolt does kind of the same thing as well:
http://www.youtube.com/watch?v=Vno5qQmE6qk&feature=channelHere's a youtube video of Ben Johnson:
http://www.youtube.com/watch?v=-gFXa4AcD5wHe runs without moving his upper body so much.
My first reaction would be to think that the style of Ben Johnson in the second video is much more efficient but Tyson Gay and definitely Usain Bolt are both two of the best sprinters in history and it would seem strange that one of them would have bad form. They both have been running for a while under coaches which have helped them constantly improve so if there was something that could be fixed as easily as that side to side movement then they would have fixed it.
What would cause them to run differently and what would be the advantages of each type of style? Does it have to do with the fact that Ben was one of the greatest starters while Tyson and Usain are known as two of the greatest finishers?