Muscle mass?! Lulz, I'm pretty heavy built myself. Also, I lift weights everyday...well, almost everyday 8)
I can't gain weight! I don't understand it. I just went and had one HUGE-ass meal, with just about every food group imaginable, and lost a pound and a half.
I'm now at 142. It's basically all muscle, but I can't gain any goddamn weight, so what good does it do?
NOTE: I used to be really deep into body building. A couple of years ago, I was much more ripped (although heavier as well) than I am now. I'd spend half of every day just exercising, or eating bulk-up foods. Now, I don't exercise at all, I just happen to have a rather physical job.