The bigger we are (more mass) and the faster we can rotate, the more energy we create to couple with the pull, and the faster we swim.
All of the elite swimmers of the world rotate their bodies along the long axis, the axis that their body is moving down the pool, while swimming freestyle and backstroke. They don’t just rotate a little bit. They rotate a lot. The question is, why?
It is commonly believed by both coaches and swimmers that the reason for rotating the body is to reduce frontal drag; that the body has a lower drag coefficient on its side than it does on its stomach. Although I am all for reducing frontal drag, I do not believe that this is the reason that we rotate. I do not believe that the drag coefficient of the human body is significantly different in the water on its side than it is on its stomach. If it were, we would be kicking faster times on our sides … but we don’t.