magazine issue 12 2006 / Issue 1

Does Exercise Truly Make You Happy?

• written by Daniëlle van Versendaal
• edited by Hans IJzerman

A healthy mind in a healthy body or mens sane in corpore sano, as Decimus Junius Juvenalis put it in his time, is a phrase that seems to imply some causal relationship between exercise and a sound mind. However, when Juvenalis (one of the great Roman satirists of his time) made himself immortal with these words, he at least seemed to care to make a causal statement. Juvenal's complete statement is actually:

"If and only if there is anything worth praying for at all, then if you must,pray for a healthy mind in a healthy body, a valiant hearth without fear of death,that reckons longevity the least among Nature's gifts, that's strong to endure all kind of toil, that's untainted by lust and anger, that prefers the sorrows of labours of Hercules..."

First rule of methodology: Be careful with causality

Proving causality has always been tough in the social sciences, as one needs a well-designed experiment in order to make more of a mere correlation. I will argue here that although exercise is healthy it does not necessarily increases your psychological well-being. More research is needed to elucidate the mechanisms behind the relationship between exercise and well-being. Although it would be great if we could aid people by letting them exercise regularly, more knowledge is needed in order to interpret the ambiguous results obtained through clinical trials in which depressed patients are treated via an exercise program.

The World Health Organization advises at least half an hour of extensive exercise per day in order to stay in healthy shape. It is thought that people who do not exercise on a regular base are more often anxious, depressed, and have lower self-esteem than people who do not exercise (Lawlor & Hopker, 2001). Exercise as an intervention has been studied extensively. Most studies focus on clinical patients comparing the effects of exercise treatment programs to other intervention strategies. Most studies expect to find a causal relationship where exercise positively influences well-being. However, this is hardly studied directly. Hence, a more critical view is vital for examining possible causality between exercise and well-being. Moreover, more knowledge of the underlying mechanisms of the effects of exercise on the brain is necessitated, a few examples of which will be given in this article.

The effect of exercise on depression

The psychological definition of well-being in exercise literature is very ambiguous, as it can be defined in multiple ways. In exercise literature, the main factors of psychological well-being that are being studied are stress reactivity, anxiety, depression, self-esteem or body image, and, finally, restful sleep. The current essay particularly revolves around the relationship between exercise and depression.

In recent years, clinicians have used physical exercise as a treatment for depression. Therefore, the benefits of exercise and depression are predominantly tested within the use of clinical trials, in a quasi-experimental setting in order to test their causality hypothesis. In general, most studies find a consistent but moderate positive correlation. Furthermore, it seems that exercise as a treatment for depression gives better results than no treatment at all, although it is as effective as other forms of treatment such as medication or cognitive therapy (Moore & Blumenthal, 1998).

For depression and anxiety, most studies use data from clinical patients instead of a random trial, drawn from the general population. From these data it is often seen that subjects with high scores on anxiety or depression and low scores on exercise benefit the most from exercise programs (Scully, Kremer, Meade, Graham, & Dudgeon, 1998). An explanation for this observation is that highly depressed or anxious people are more likely to get well anyway, since they are in the top segment of how depressed or anxious someone can be.