Acute Effects of Exercise

Taken the meager experimental support from well- designed training studies, how can we explain the commonly held belief in the stress-alleviating effects of exercise and the fact that many exercisers state to be motivated by stress reduction and increased psychological well-being? The source of this belief may be largely found in the acute psychological effects of exercise. In the training studies described previously, psychological and psychophysiological testing was preferably done when subjects had not been exercising for a few days.

This was done to prevent confounding of the results by possible acute effects of exercise. Studies that have specifically addressed these acute exercise effects have provided evidence of improved mood, reduced feelings of tension, anxiety, and anger, and increased feelings of vigor directly after exercise. This acute feeling better effect of exercise is paralleled by various physiological effects. Although heart rate generally remains elevated above the base level, postexercise blood pressure is seen to decrease below base level for several hours. Neuromuscular activity and peripheral pulse volume are decreased, and brain alpha activity, an indicator of a relaxed but alert mental state, is increased. Most importantly, there is evidence of reduced heart rate and blood pressure responses to stress in the hours directly after the exercise.

Among the hypothesized mechanisms for the acute psychological and physiological effects of exercise, those related to the endogenous opioids have been most often cited. An endogenous opioid, beta-endorphin, has been held responsible for the euphoric (after) effect of running, which has been ominously termed runner’s high, and for a benign endorphin-mediated exercise addiction. However, elevations in peripheral beta-endorphin (a typical distress hormone often coreleased with adrenocorticotropin) are seen only during strenuous exercise, not during mild to moderate exercise.

More importantly, beta-endorphin levels are associated with negative mood, i.e., expectation of future pain and exhaustion, rather than positive mood, even during exercise. Finally, the opiate antagonist naloxone does not prevent the exercise-induced elevation in the pain threshold or mood improvement, suggesting that these are largely independent of endorphin action. Since monoaminergic systems in the brain are involved in the pathogenesis of depression and anxiety, a more plausible explanation for exercise-induced mood effects may reside in its effect on central monoamines.

Animal models suggest that exercising increases noradrenalin and dopamine metabolism in the brain and that it also increases brain serotonin content. It shares these effects with antidepressive like MAO inhibitors and serotonin-reuptake blockers. Beneficial effects on monoaminergic neurotransmission may also explain why improved mood after training programs is most often found in groups of highly anxious or depressed subjects. An improvement in monoaminergic neurotransmission may be effective only if it is severely compromised, as is the case in anxiety and depression.

Whatever the physiological and psychological causes, the tight contingency between exercise and the mood improvement directly afterward forms a solid basis for the popular belief that exercise relieves stress. Exercising may be an excellent short-term coping strategy that helps people to unwind more rapidly from daily pressures experienced in the school, job, or home environment, even if effects on mood are short-lasting. Likewise, the accumulation of episodes of blunted cardiovascular responsiveness may reduce the health risks of stress, even if reductions in stress reactivity are confined to stressors encountered in the postexercise periods.

For exercisers, exercising may become a major coping strategy, up to a point where stopping exercise could lead to loss of well-being and self-esteem. In fact, most of the popular ideas on the psychological benefits of exercise may stem from exercisers themselves. It must be noted, however, that in most Western countries only 10 to 15% of the population are engaged in exercise with high enough intensity (>70% maximal heart rate), duration (minimally 20 min), and frequency (three times a week) to maintain aerobic fitness level.

About 60% have irregular exercise habits or perform mild exercise only, e.g., regular walking or bicycling. The remaining 25% are nearly completely sedentary, and this figure appears to be rather resistant to 50 years of campaigning to increase physical activity. A major future research question is why exercisers exercise and why nonexercisers do not.