I guess if he would stop moonballing from 10 meters behind the baseline he could make life a lot easier for himself and not run out of steam in the QF and SF of tournaments. That said, he needs to add more muscle.
Why do you say that? He's proven to be able to hit the ball as hard as anyone on tour when he decides to. What advantages would added muscle give a player like Monfils?
I think he just needs to get a much more offensive mindset, especially in pressure situations. I think that against Nadal he knew that if he wasn't aggressive, Nadal would have made him pay for it. But against Roddick, he thought that he could hang back and Roddick would let him have it. He needs to keep his intensity up under pressure