I've never quite understood how this works. The balls speed and spin can be exactly the same between a heavy hitter and normal hitter, but the difficulty in returning it is huge, and can actually seem like you are getting pushed off the court.
When I was a kid, I hit with an older ex high level touring pro (top 20). His strokes didn't look that fast and weren't, but it felt like you were being physically pushed off the court on every stroke. When I asked him about it, he mentioned it was just getting your body behind the ball and good hip turn. I have a pretty big forehand, but it is mostly arm and shoulder and not heavy.