Gym - Targeting the same muscle group TWICE in 7 days. Ok?

If you're hitting your muscles hard then its best to let them rest. Building up muscle takes a lot of time and you might think that doing lots of heavy training will make them grow but it can actually have the opposite effect. Avoid over training at all costs. Even though you feel that you can do more with the muscle group in a week it can take almost 5 days for muscles to completely repair itself after a heavy workout. Remember you don't build muscles at the gym, you break them there, rest and recuperation is what builds your muscles.