As a drummer, I can say that drumming does give your arm muscles (all of them, not just biceps) a boost. I'm always asked whether I work out a lot, but I really don't. So, it's not the biceps that influence the drumming, it's the other way around
To stay on-topic: I really think Larry looked awful in U23D. Not only skinny, but also his face looked 10 years older. I think he took a few shots of bull-blood since then, because he's looking great in the Q mag