What is enough exercise for the body to shift into shape? Stimulation happens inside the gym - results come from what we do (or don't do) otherwise : sleep, nutrition, rest, time for recuperation and overcompensation. Remember, we are literally tearing muscle tissue as we diligently execute those strength inducing lifts in the gym.
But then what??
Recovery is key so that next workout you are in fact stronger.
Think about digging a hole: the deeper you dig that hole, more resources are needed to fill that hole back up and then some, before you can go digging again. Your body only has a finite amount of recovery resources designated for workout A, before you start ripping, tearing and slashing precious muscle tissue again!!!!
It's not how much exercise the body can handle, it is how little it requires to make that shift into shape - then, rest, eat well, sleep tight and GROW happily ever after:-)