Health Risks of Exercise

The potential adverse effects of exercise are important considerations in evaluating exercise as a stressmanagement technique. It is important to note that although exercise is widely regarded as a beneficial activity, exercise may be associated with untoward events in susceptible individuals.

However, even in cardiac patients, the potential adverse effects of exercise such as arrhythmias and myocardial infarction are relatively rare and occur in less than 1 of 10 000 exercise tests and at a rate of less than 1 per 100 000 h of exercise training. Minor muscle aches and joint pains are common - either as a result of overuse or acute trauma - but are usually self-limited.

Major orthopedic problems are very uncommon in supervised exercise settings, but may be more common in unsupervised programs or in individuals who fail to comply with exercise prescriptions. The annual rate of exercise-related injury in adults is roughly 10%, with only 5% requiring medical care. These injuries often result from a sudden unexpected trauma, such as twisting an ankle.

Proper warm-up and stretching are useful preventative measures. Overuse injuries, on the other hand, are a result of chronic, accumulated stress on the musculoskeletal system. This type of injury is more common in high-impact, weightbearing activities such as jogging and includes such problems as tendonitis, stress fractures, and ruptured disks in the lower back. Gradual progression of exercise, attention to environmental factors (e.g., heat and humidity, altitude), and the use of proper equipment all serve to reduce the risk of injury.

Exercise addiction is a term related to overuse and is generally described as an addiction of psychological and/or physiological nature to regular physical activity, characterized by withdrawal symptoms after 2 to 3 days without exercise.

Although exercise as a compulsive behavior has been characterized as a positive addiction that promotes well-being, the potential for abuse has been recently recognized. Individuals may experience depression, anxiety, and irritability if they are unable to exercise. There is some evidence that exercise addiction can have an adverse impact on interpersonal and occupational functioning, as well as on self-esteem.

There is also some suggestion of overlap between excessive exercise and eating disorders. Obligatory running in men, for example, has been likened to anorexia nervosa in women. However, there is little empirical support for the notion that either the etiology or level of psychopathology is comparable between anorectics and compulsive exercisers. Eating disorders also may be more prevalent among women, particularly among participants in certain forms of exercise (e.g., ballet, gymnastics, and figure skating).

Mechanisms. The mechanisms by which exercise reduces stress are not known. A number of psychological mechanisms have been proposed, including increased self-efficacy, a sense of mastery, positive thoughts, distraction from negative thoughts, and enhanced self-concept, which in turn can lead to improved mood. Exercise may also be a form of meditation that triggers a more relaxed state or a form of biofeedback that teaches people to regulate their autonomic arousal. Exercise may also be associated with social reinforcement. There is not, however, definitive evidence to support any one explanation.

A number of biological mechanisms also have been suggested, although there is no consensus as to the precise mechanism whereby stress is reduced. There are data to suggest that the antidepressant effect of chronic exercise may be mediated by increased central norepinephrine neurotransmission.

Changes in the hypothalamic-pituitary-adrenocortical axis may also be related to improved mood due to the lessened cortisol response to submaximal exercise following exercise training. Increased levels of ß-endorphins may also contribute to the antidepressant effects of exercise. However, most studies have failed to employ adequate methodologies to accurately measure circulating endorphin levels in the brain.

Table 1. Stress-related changes with chronic aerobic exercise

Summary and Future Directions. Both acute exercise and chronic exercise have been shown to reduce stress responses measured behaviorally, psychologically, and physiologically (see Table 1). Research efforts are currently directed at identifying those individuals who are most likely to benefit from exercise, at examining the mechanisms by which exercise reduces stress, and at developing strategies for improving long-term adherence to exercise and for motivating people to initiate exercise behavior.