Compare that to the average upper body of a cyclist or a runner. Remember that Greg Lemond was worried about a bit of extra shoulder muscle after some cross country skiing in winter!
Once you have this kind of upper body muscle you can focus on your stroke. You can eke out some extra speed by changing your position a little bit. You can do all the things the swim books tell you to do.
What is also striking when you see Bernard is the size of his hands and feet. He has veritable flippers, but so does Thorpe and so does Phelps.