Yesterday I started a program that should, in 6 weeks time, have me pulling off 10-15 pull-ups at a time. As for now, I can struggle to about 4, give or take 3. It's not that I'm out of shape or weak--on the contrary, everything I've done lately has involved leg power. Running, hiking, cycling, snowboarding, kicking field goals, etc. While typing on the internet and playing NES games does involve some small muscles in the forearms, you'd need many hours of Burgertime to get those muscles strong enough to lift anything heavier than a cream-laden Twinkee.
Coincidentally, last night I watched a special on TLC called "The Man Whose Arms Exploded". The title doesn't pull any punches; the story documents a guy who used so many steroids it looked liked he stuffed a pair of suitcases into his upper arms. Eventually, the muscles exploded, shrinking his beefed-up roid-filled arms to a more modest size, say that of two toasters per arm. It makes me wonder what might happen is Barry Bonds' head does the same thing.
