Exercise. General Methodological Issues

The empirical evidence for the relation between exercise and stress is derived from multiple disciplines (psychology, exercise physiology, psychophysiology, physical therapy, etc.) that may approach the topic from different perspectives and conceptual models. The type of experimental design (e.g., cross-sectional, longitudinal, or interventional) is an important consideration.

Cross-sectional studies typically compare stress responses of fit versus unfit groups, athletes versus nonathletes, or people who engage in one form of exercise with individuals who engage in different exercise (e.g., joggers vs. weight lifters). Because of the correlational nature of cross-sectional studies, however, causal attributions are not possible.

Longitudinal designs also are correlational and typically follow subjects who engage in different kinds of exercise over time. Interventional studies typically involve the assignment of individuals to either exercise or nonexercise conditions and compare the groups over time. Random group assignment is necessary to attribute differences in outcomes to the intervention. Control groups, another important design consideration, should be matched as closely as possible to the experimental group on nonspecific variables (e.g., demand characteristics, experimental contact, and social support).

Other important issues include methods for assessment of aerobic fitness operationally and procedures for measuring stress. Although there are a number of ways to measure aerobic fitness (e.g., questionnaires, 10-min walk/run, step test, and treadmill test), the most precise assessment of aerobic fitness involves a multistage maximal exercise test on a treadmill or cycle ergometer with direct measurements of oxygen consumption.

Stress responses can be measured by self-report questionnaires or may be measured physiologically. For example, heart rate and blood pressure are commonly used measures of stress response, most likely due to their ease of measurement and sensitivity to differences in fitness levels. The selection of laboratory stressors is important because the stressor must elicit a strong psychophysiological or subjective response that is measurable and potentially modifiable.

The most commonly used stressors include cognitive tasks such as mental arithmetic, the Stroop Test, or public speaking; performance tasks such as the Mirror Trace Task or video games; or physical tasks such as the hand dynamometer test or cold-pressor test. Ideally, a number of stressors, varying in intensity and patterns of physiological response, may be used most effectively in identifying changes in stress reactivity.

Other physiological indices of stress, and particularly of sympathetic nervous system activation, such as secretion of urinary catecholamines, also may be used to provide an overall physiological index of stress. Adherence is another important issue in exercise research, particularly because of the high rates of nonadherence. It has been estimated that more than 50% of people who initiate an exercise program will terminate the program within the first several months.

This issue is especially relevant in light of the fact that exercise must be maintained in order to achieve its physical and mental health benefits. Such strategies for improving compliance have been the focus of much research.