Models

Both single- and multi-stressor models have been proposed. The single model emphasizes an imbalance between training load and recovery and excludes factors unrelated to physical performance. The multi-stressor model incorporates non-physical factors including psychological, emotional and social aspects. An integrative model is also suggested that incorporates recovery from training and how stressors impact an athlete including assessment of stressors based on athlete personality.^[1]

Addiction

Physical exercise may be addictive. One theory is that this addiction is due to natural endorphins generated by the exercise.^[2] Whether strictly due to this chemical by-product or not, some people can be said to become addicted to or fixated on psychological/physical effects of physical exercise and fitness.^[3] This may lead to overexercise, resulting in the "overtraining" syndrome.^[4]

[edit]Physiology

Improvements in strength and fitness occur only after the rest period following hard training (see supercompensation). This process can take days to complete, depending on the intensity and duration of exercise leading to the overtrained state. If sufficient rest is not available, then complete regeneration cannot occur. If this imbalance between excess training and inadequate rest persists, then the individual's performance will eventually plateau and decline. Mild over training may require several days of rest or reduced activity to fully restore an athlete's fitness. If prompt attention is not given to the developing state and an athlete continues to train and accumulate fatigue, the condition may come to persist for weeks.^[5]

Overtraining occurs more readily if the individual is simultaneously exposed to other physical and psychological stressors, such as jet lag, ongoing illness, overwork,menstruation, poor nutrition etc. It is a particular problem for bodybuilders and other dieters who engage in intense exercise while limiting their food intake.

A number of possible mechanisms for overtraining have been proposed:

• Microtrauma to the muscles are created faster than the body can heal them.
• Amino acids are used up faster than they are supplied in the diet. This is sometimes called "protein deficiency".
• The body becomes calorie-deficient and the rate of break down of muscle tissue increases.
• Levels of cortisol (the "stress" hormone) are elevated for long periods of time.
• The body spends more time in a catabolic state than an anabolic state (perhaps as a result of elevated cortisol levels).
• Excessive strain to the nervous system during training.