I wouldn't do two-a-days unless you have really good genetics, and even then you can still overdo it. If you can pack on muscle easily, it may work for you. Otherwise, it would most likely be counter productive. Even if I were taking something hormonal, I wouldn't do two-a-days.
**** you, Joe Weider!
I've gotten a lot of results by working each muscle twice per week with lower volumes.
The central nervous system is the thing a lot of people forget about. If you put a lot of physical stress on the body too frequently, you're bound to have problems eventually. Muscle contractions can occur because of certain chemical reactions taking place within your CNS. You can tax these to the point of CNS fatigue, which is something you want to avoid if your goal is to improve athleticism, or build muscle, or lose fat or whatever else. The more taxed your CNS becomes, the more you'll have to rest to allow it to recuperate. The CNS can recover and deal with physical stresses much better if you train less frequently (i.e, 3-4 times per week, or 5 for some). Keep your CNS happy!
So yeah, unless you're very mesomorphic, I'd steer clear. That's my opinion anyway.
