Training at intensity is absolutely necessary to gain muscle quickly. However, over-training is something completely different.

In the gym it’s very difficult to over-train if you’re training intensely because your body won’t really let you get there. It will tell you that you’re overdoing it with nausea, dizziness and “hyper fatigue”.

Overtraining is more commonly experienced by working out before your body has fully recovered.

So if you work out with intensity on Monday and you go back to the gym on Tuesday to work out at even more intensity (which you should be aiming for – or at least more weight) then you’re going to overtrain which can lead to muscle atrophy.

So my advice to you would be to work out with intensity – so that the last reps of your last set are almost not possible, eat well, drink well, rest well and make sure that you can lift more than the last time OR do the work out faster than last time.

This way you’ll know if your muscles have repaired or not. If you can’t do those things then you would be better off just going home and resting another day.