How would you hit the ball so that it has a huge amount of topspin like rafael nadal does?

It is not about the muscles at all, it is about skill and movement. To be able to hit a top spin like Rafael Nadal you need to move your legs a lot, bend your knees, and make sure that you come under the ball with your racket when hitting. Nadal also has a special swing where he rotates his arm over his head, this will help you generate more speed as well. Everybody has a different stroke, but the main idea of top spin is to bend your knees and come under the ball with your racket when you are about to hit. There are also some rackets that will help you generate extra top sping like Nadal's racket the Babolat Aero Pro Drive.