The weak link in the physical performance chain is not training, but restitution. Restitution encompasses nutrition, immune function, physical therapy and message, relaxation etc. The best athletes are able to train more intensely in specific training sessions because they know when to reduce intensity at other times and let the body recover. Even among elite athletes, we see many who are motivated to train hard every day. As a result, every training session is at fairly high intensity.
None are sufficiently low enough to promote recovery.
And because of chronic fatigue, none are intense enough to drive continued improvement maximal capacity in a body that is already very well trained. The interesting thing for the rest of us is that the same rules apply. We may only train 10-15 hours a week instead of 30, but if all of our training is too intense, the results are just as unsatisfactory as when we do not do enough high intensity training. Not everybody has the capacity to tolerate 30 hours a week of training. Very few do, actually.