The thing about most rappers’ physiques is that they have a natural advantage. They are genetically more suited for athletics. That’s why they have the muscles of the back of the body – the ones responsible for athleticism (calves, hamstrings, glutes, lower and upper back and traps) easily developed.
Ja Rule is not a big guy. He looks good because he has a decent amount of muscle and is naturally very lean. It doesn’t hurt that they have naturally lower levels of body fat. All that is left is to develop the muscles of the front of the body – biceps and chest and you’ve got yourself a beach physique.