Overtraining is a physical, behavioral, and emotional condition that occurs when the volume and intensity of an individual's exercise exceeds their recovery capacity. They cease making progress, and can even begin to lose strength and fitness. Overtraining is a common problem in weight training, but it can also be experienced by runners and other athletes. Split training can help with overtraining.
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.
Like pharmacological drugs, physical exercise may be chemically addictive. One theory is that this addiction is due to natural endorphins and dopamine generated and regulated by the exercise. 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. This may lead to overexercise, resulting in the "overtraining" syndrome.
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 overtraining 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.
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.
- Persistent muscle soreness
- Persistent fatigue
- Elevated resting heart rate
- Reduced heart rate variability
- Increased susceptibility to infections
- Increased incidence of injuries
- Mental breakdown
Listed below are some of the common effects and cited signs of overtraining. Not all of the following effects will occur. The presence of any of these symptoms does not imply that an individual is overtrained. 
- Excessive weight loss
- Excessive loss of body fat
- Increased resting heart rate
- Decreased muscular strength
- Increased submaximal heart rate
- Inability to complete workouts
- Chronic muscle soreness
- Increased incidence of injury
- Depressed immune system
- Constipation or diarrhea
- Absence of menstruation
- Frequent minor infections/colds
- Heart Palpitations
- Lower Testosterone Levels
- Higher Cortisol Levels
- Loss of appetite
- Mood Disturbance
- Loss of motivation
- Loss of enthusiasm
- Loss of competitive drive
- Early onset of fatigue
- Decreased aerobic capacity
- Poor physical performance
- Inability to complete workouts
- Delayed recovery
Allowing more time for the body to recover:
- Taking a break from training to allow time for recovery.
- Reducing the volume and/or the intensity of the training.
- Suitable periodization of training.
- Splitting the training program so that different sets of muscles are worked on different days.
- Increase sleep time.
- Deep-tissue or sports massage of the affected muscles.
- Self-massage or rub down of the affected muscles.
- Cryotherapy and thermotherapy.
- Temperature contrast therapy (contrast showers etc.).
- Ensuring that calorie intake at least matches expenditure.
- Ensuring total calories are from a suitable macronutrient ratio.
- Addressing vitamin deficiencies with nutritional supplements.
Overtraining can be used advantageously, as when a bodybuilder is purposely overtrained for a brief period of time to supercompensate during a regeneration phase. These are known as "shock micro-cycles" and were a key training technique used by Soviet athletes.
- Exercise addiction
- National Academy of Sports Medicine
- Physical fitness
- Personal Trainer
- Social influences on fitness behavior
- Sports psychology
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