i agree with almost what everyone have already said.. But over training can happen if you're natural, the body will get burnt out and you start feeling weak i have experienced this myself, however on steroid i do not believe in overtraining at all if youre diet is in check and getting plenty of rest, im on 90mg anavar, and i been working out everyday 7 days a week, 5 times a week weights and cardio and abs everyday atleast minimum of 1.5 hour of exercise daily, and on my lifting days im at the gym 2-3 hours with cardio and abs thrown in there, and im making gains everyday, getting stronger bigger leaner day by day., been doing this for 3 straight month with no off days.
Just my opinion