Within a single training week or longer training periods, there has to be a balance between hard training, light training, and rest. When a hard training session or training period causes a significant disturbance in the body's homeostasis, it must be followed by sufficient recovery if performance improvements are to be optimized. The importance of sufficient recovery is due to the fact that performance improvements actually occur during recovery from training and not during workouts. Therefore, maximum performance is the result determining the correct balance between training load and recovery.
Periodization is an important principle in training. Usually athletes have several very hard training periods each year, during which both the intensity and volume of training are very high. These kind of overreaching periods are very exhaustive but necessary for athletes to further improve their performance. However, performance can improve only if hard training is followed by adequate recovery.
Excessive training without sufficient rest may lead to overtraining, which is characterized by a decrease in performance, and even, in the worst cases, can have harmful effects on health. Recovery from overtraining may take several weeks to even months. It is even possible that chronic overtraining can cause an athlete to never reach the same level of performance as before overtraining occurred. Therefore, it is paramount that prevention of overtraining is systematically implemented into any training regimen.