It's a fairly common gung ho newbie mistake to spend too much time banging out reps and not enough time recovering. While it's great to be enthusiastic about attaining muscle size and strength goals, research published in the journal Anatomical Record shows what can happen when you aren't smart about workout planning.
One group of lab rats engaged in simulated weight training 5 days a week while another group didn't do any training at all. When the experiment was over, the hard-training rodents had less muscle mass than the ones who just walked around in their cage. So overtraining can actually lead to muscle atrophy. Try splitting up your workouts so each muscle groups has at least 48 hours to recover between sessions. For recent research on kick-starting the recovery process, read today's Breaking News post at OptimumNutrition.com