I trained as a bodypump instructor a few years back. It's all about low weight and high reps. There was one guy who was training to instruct and he was a "power lifter" at first. You know - all bulky, couldn't lower his arms all the way. After a few months teaching bodypump, he really slimmed down and was pretty easy on the eyes.
If you're wondering if I stopped instructing because I didn't like bodypump - well...that's one reason. I wasn't crazy about it. But mostly it's because I'm a rather shy person and didn't like instructing at all. It was an attempt to do something out of my comfort zone. Plus, I really prefer to exercise alone at my house.