magazine issue 12 2006 / Issue 1

Does Exercise Truly Make You Happy?

• written by Daniëlle van Versendaal
• edited by Hans IJzerman

Cordain Gotschall, Eaton, and Eaton (1998) hypothesized from an evolutionary perspective that human genotype responsible for physical activity is roughly the same as our ancestors that were hunter-gatherers. Our energy expenditure only accounts for 38% of our energy intake. It seems that current-day society demands less physical activity from us then the Paleolithic society 10.000 years ago. There are several studies that focus on activity requirements. From these it is concluded that people (and especially women) are exercising less when they get older. What could be the reason for this decline? Tergerson and King (2002) studied motivations and barriers that explain exercise and compared men and women. They found that men and women differ in their motivation; Women focus on their health, while men intend to gain strength.

A physiological mechanism that could account for both motivation to exercise and the positive effect on psychological well-being could be that of changes in brain endorphins (Dishman, 1997). More specifically, it is thought that beta-endorphin, a hormone released from the pituitary gland during vigorous exercise may be responsible (Goldfarb & Jamurtas, 1997). Exercise is healthy for us and is thus rewarded in our brains. Most organisms seem to be biologically driven to stay physically active. Caged rodents are often seen to run for several hours a day in their little wheel, although they certainly do not need to run a mile in order to obtain food or escape natural predators. The changes in the brain’s endorphins affects mood and can make exercise very addictive. One could probably even say that people engaged in professional sports probably are addicted for achievement!

The effects of exercise are not observed immediately

More research is needed in order to confirm that exercise can truly counter depression. One of the goals is to establish a better understanding of the amount of exercise needed in order to see its effects. This is referred to as the dose-response relation in exercise treatment. Analyses of multiple studies (so called meta-analyses) have been conducted in order to determine the effective duration as well as the most effective type of exercise as an intervention. Many meta-analysis studies have encountered difficulties in comparing different results because the research designs differ remarkably. A good meta-analysis by Lawlor and Hopker (2001) selected 16 out of 72 relevant studies, including those with several exercise paradigms, several depression scales and designs with healthy and non-healthy subjects. Their findings were that several exercise paradigms had similar effects on depression. While other studies have found that for treatment of anxiety aerobic chronic exercise is more beneficial than non-aerobic exercise such as strength training (Petruzello, Landers Hatfiel, Kubitz, Salazer, 1991). Most meta reviews suggest that exercise programs are beneficial in depression after 4 to 6 weeks of intervention (Scully, Kremer, Meade, Graham, & Dudgeon, 1998). Unfortunately, only one of the studies reviewed by Lawlor and Hopker (2001) performed a follow up test of depression and found that the exercise intervention had no long-term effect.

In conclusion

In order to gain a more proper understanding of the causal relationship between exercise and depression (if any), one should examine several environmental and physiological mechanisms that are involved, as well as the use of random trials, drawn from the general population. For example, at the Vrije Universiteit in Amsterdam, a large study is now conducted in order to study the heritability of exercise behavior as well as the genetic factors involved with depression. A multidisciplinary study is unavoidable if we do not wish to be trapped into assuming that a correlation is the same as a causal relationship.

There is no reason to believe that exercise is not healthy of course. Do not let this article prevent you from going to the gym because of some scientific doubts on the psychological advantages (unless you were looking for an excuse to get out of exercising. By all means, stay home and relax). To answer the first question: does exercise make you happy? Not necessarily, and as an intervention for depression, surely it will not hurt. Just remember to stay critical, and most of all, inquisitive. Science still has a lot to unravel in our world and a lot of bright minds will have to put their heads together, for solving questions as these.