Psychophysiological reactivity to psychological stressors as a function of cardiovascular fitness and exercise

Abstract

Although it has been frequently claimed that regular physical exercise possesses stress-reducing properties, the actual scientific evidence which exists to support this claim is sparse. In addition, the relevant literature has almost exclusively emphasized endurance forms of exercise which contribute to an enhancement of cardiovascular fitness levels. When assessing the effects of cardiovascular fitness alone, the variables of fitness and exercise are by definition confounded, since it is difficult to enhance cardiovascular fitness without regular exercise. It is possible however, to regularly engage in some forms of exercise without significantly increasing cardiovascular fitness. The present study was designed to examine the effects of stress induction on several psychophysiological measures as a function of both cardiovascular fitness and exercise. Fifty-five male subjects were exposed to four psychological stressors, and effects on heart rate, tonic skin conductance levels, digital skin temperature, and forearm electromyogram were assessed. General linear model analyses revealed three major findings: 1. While quantity of exercise made no difference for Ss with high fitness levels, for Ss with low fitness levels high quantities of exercise resulted in a potentiation of the stress response. This was interpreted to mean that when an individual's fitness level is low. the act of engaging in high quantities of exercise may actually serve as a stressor itself. 2. When differences in stressor levels were controlled. Ss high in cardiovascular fitness demonstrated lower heart rate levels white recovering from exposure to the stressors. These results suggest that there may be a limited reduction in physiological reactivity to psychological stressors as a function of cardiovascular fitness. 3. When frequency of exercise was held constant, Ss who spent less time per session of exercise showed lower recovery skin conductance levels than those who spent more time per exercise session. suggesting there may be some optimal relationship between frequency and amount of exercise for reducing reactivity to psychological stressors. The results of this study clearly challenge the simple notion that "exercise reduces stress", and indicate that at the least this relationship is mediated by interrelationships between cardiovascular fitness, amount of exercise, and frequency of exercise.