Originally Posted by camisadelgolf
In theory, it's kind of up to him. Bulking up would slow him down, so the preference might be that he never develops 5-10 home run power.
I don't buy that bulking up would slow him down. Have you ever seen what Olympic sprinters are built like? Those guys are jacked. As long as Billy made sure to concentrate on his lower body rather than his beach muscles, he could stand to gain a lot of size without getting so large that it would impact his speed.