Exercise offers benefits even when people schedule it on their own

Dozens of studies have confirmed both psychological and physical benefits of exercise. The results seem clear enough: a regular program of cardiovascular exercise has been shown not only to promote physical well being, but also to abate depression, decrease anxiety, and improve overall quality of life. But James Annesi noted that most of these studies were implemented the same way: participants agree to a preset program of exercise, carefully controlled and monitored by experimenters. Might the psychological benefits only be an artifact of all the attention they were getting? It's possible, for example, that the positive results might merely have been the result of the Hawthorne effect (which we've discussed here): the simple fact that they were being studied may have improved the participants' sense of well-being.

Annesi designed a study to try to minimize the impact of the experimenter by putting participants in charge of their own exercise programs. He recruited forty-two adults to take part in a simple study. These were people who had already chosen on their own to enroll in a community fitness center, and instead of following a carefully planned routine, the participants were allowed to choose between exercise bikes, treadmills, rowing machines, or elliptical trainers. Further, there was no required regimen—they could exercise as long and frequently as they wanted (or as quickly and infrequently). The only guidance they were given was a one-page sheet indicating that three or more cardiovascular sessions per week of 20 to 30 minutes could improve fitness. The only requirement was that the participants agreed to not do any other type of exercise outside of the fitness center, for a period of twelve weeks.

Annesi measured fitness with a treadmill test and measured indicators of Depression and Tension using the Profile of Mood States, a short questionnaire that gave people words describing emotions and asked them how much they were felt those emotions during the past week. He took the same measurements after the 12 weeks were completed. Here's a summary of the results:

Both Depression and Tension scores were significantly lower, for both men and women—even when their responses initially fell in the "normal" range. There was also a small improvement in cardiovascular fitness (as measured by maximum oxygen intake), but this was not correlated with either of the two measures of mental health. Even though participants averaged under two exercise sessions per week (about 20 sessions on average for the entire 12 weeks), they still achieved significant mental and physical health benefits. Since the influence of the experimenter was minimal compared to other studies, Annesi argues that the benefits of exercise are likely due to the exercise itself, rather than the artifice of the study.

Annesi, J.J. (2003). Sex differences in relations of cardiorespiratory and mood changes associated with self-selected amounts of cardiovascular exercise. Psychological Reports, 93, 1339-1346.