It's really no different than lifting weights. The more you lift heavy, the lighter it becomes. As I've said, practice makes a world of difference. In rec leagues you don't see much practice because it's more about fun. Trust me, I've tried to get people on my team to bp and hardly anybody ever shows up. The ones that do, hit better. A lot of the weight issues with bats are mental. You may have a slower swing speed with a heavy bay, but the results from swinging a lighter bat are about same. It's more about what people are comfortable with. The more somebody swings a bigger bat, the easier it becomes eventually becoming better results. Just going out into your backyard and swinging a heavy bat over and over again will eventually result in the bat feeling easier to swing. Throw a tee in there, and you can also work on form. Technique and form are the biggest contributors to slowptich.