That as you get stronger and bigger, you don't do more exercise, you do less because the stresses are growing greater. In other words, a beginner is too damn weak to overtrain. But as you grow bigger and stronger and you're handling 500 pound squats, you can overtrain very easily, so you don't train more. As you grow bigger and stronger, you train less and you'll keep growing. As the weights grow progressively greater than the stresses also grow progressively greater too. If you don't do something to compensate for the ever growing stress, the stretches will reach a critical point such that they constitute over training.
The first course will be a slowdown in progress, and if you continue with the same exact volume and frequency protocol, there will ultimately be a complete cessation of progress known as a sticking point. This can be prevented by inserting extra rest days and taking layoffs. You should never have to reach a sticking point.
