I found out about overtyraining the hard way. On my first 1-test/4-AD cycle, my strength shot through the roof and I started working each bodypart twice a week...to absolute failure. in my 5th week, I began to lose strength, and by cycle's end, I was down in bed with flu for the first time in years. I NEVER, EVER get sick. But I did gain 15 lbs in the first 2 weeks!
I am stronger now than I was then on ph, and I work each part once a week, and I never lose size either. If you can comb your hair as you leave the gym on arm night, you're not pumped enough.