Rest is responsible for 50% of the performance! Without unnecessary succeed him to think anything. This is what keeps you from falling into overtraining and also making your progress possible. The rest takes many forms. Lack of drive, moderate activity, sleep overall lifestyle. Sleep is the most visible moment of rest since that when the body is in standby global stage.
The body is in sleep a bit like a computer; close to reboot but stopped in appearance. Having a good sleep quality and quantity is a strong vector of progress but also a fairly reliable indicator of good t training managemen. Sleep can be considered as an indicator of reliability to attest the quality of the workout.
If one sleeps well is that you are fit and the body easily adapts to the constraints imposed on it. If you sleep poorly is that something interferes with the functioning of the body.
The sport is not always directly responsible. But in a quality approach, the coach must take into account all aspects that make up the life of his athlete and suggest an alternative to this kind of problem.