Exercise may reduce depression — if your brain works in this specific way

The experience of depression varies depending on who you are. Unfortunately, so does the effectiveness of the treatment. While antidepressants work for some, others have been driven to use experimental options, like ketamine-based nasal spray, to soothe persistent symptoms. Others find no relief at all.

Knowing who might benefit the most from what kind of depression treatments before digging through the medicine cabinet could make relief arrive sooner. In a new study, scientists show that people with certain brain signals are more likely to benefit from one basic, effective treatment: exercise.

In a study of 66 adults with major depression, scientists found eight weeks of moderate aerobic exercise was enough to alleviate symptoms by about 55 percent. Meanwhile, light-intensity stretching reduced symptoms by 31 percent over the same period of time.

Importantly, the scientists also found a biomarker that might predict why exercise seemed to work for these patients. These individuals tended to have worse depression symptoms to start with and greater levels of reward processing in the brain.

This study tells us two things. Firstly, it adds to a growing body of evidence suggesting that aerobic exercise, even easy exercise, could help alleviate depression symptoms. It also suggests that people with greater levels of reward processing (but still worse symptoms) may benefit from exercise even more.

The study was published Monday in Psychological Medicine.

Brandon Alderman, the study's lead author and an associate professor at Rutgers University, tells Inverse that, typically, people with lower reward processing see greater improvements after traditional treatments, like therapy or drugs.

"Actually, several recent studies showed that depressed patients with lower, as opposed to greater reward processing as found in our study, experienced greater symptom improvement following treatment with cognitive-behavioral therapy and SSRIs [traditional anti-depressant drugs," he says.

This study, he continues, suggests that people who benefit most from exercise as treatment are the same that are predicted to benefit less from traditional treatments — those with greater levels of reward processing.

Measuring reward processing – Dysfunctional reward processing is thought to be a central feature of depression. In a 2018 study, Alderman found that 100 young adults with more major depression symptoms showed less activity in the reward circuits when they won money in a guessing game as the experiment progressed. They had less sensitivity to rewards over time.

In this study, before assigning an exercise plan, the team measured how the 66 participants processed rewards. They also had the players play a guessing game where they won, or lost, money by selecting a door at random, and measured the corresponding activity in their brains using an EEG.

Then participants committed to eight weeks of light stretching or moderately intense exercise – like running or cycling for 45 minutes. They worked out three times per week.

At the end of eight weeks, the results suggested exercise had no effect on how people processed rewards. However, those that had high reward processing were 45 percent more likely to respond to the exercise treatment. Those who had worse symptoms at baseline were 18 percent more likely to respond.

Unfortunately, Alderman says that it's not possible to predict how one's reward system works right now. There is some speculation that we might be able to use a questionnaire to help determine reward processing in the future.

But could reward-processing become something that's easily and frequently determined by an EEG? Perhaps: These findings are only preliminary, the study authors caution. Still, the tools to use reward processing as a biomarker already exist. The EEG measurement used in his study is "already widely used in medical practice," Alderman says.

"It's easy to imagine that the type of EEG-based measure used in our study could be more widely disseminated," he says.

Workouts and depression

Predicting treatment effectiveness aside, the study helps define how working out might serve as a treatment for depression. Moderate aerobic exercise was more effective than light stretching (though people who did light stretching did see a reduction in symptoms).

"Even light walking is beneficial for depression," Alderman says. "Our findings of a greater anti-depressant effect following moderate-intensity aerobic exercise relative to light stretching suggests that even greater benefits can be derived from more vigorous exercise."

That said, moderate-activity typically tends to be a good starting point. A 2004 review paper on the use of exercise as depression treatment suggests beginning with lower-intensity exercise activities that you enjoy. This helps create a habit, allowing you to build up from there.

This new paper suggests sticking with a regimen over time can lead to positive results. The improvements in depression symptoms were only significant at the end of the eight-week experiment. Alderman and his colleagues suggest that eight weeks might be the "minimal dose" required to feel the effects of exercise.

Eight weeks may feel like a long time to wait for results – but until measuring reward activity gets more seamless it may be worth a try.

"Exercise has been shown in countless studies to be beneficial for depression, and our data only add to the growing body of evidence," says Alderman.

Partial Abstract:

Results: Aerobic exercise resulted in a large reduction in depressive symptoms in adults with major depression. There was no impact of aerobic exercise on the RewP or ERN. In the aerobic exercise group, individuals with a larger pre-treatment RewP [odds ratio (OR) = 1.45) and increased baseline depressive symptom severity (OR= 1.18) were more likely to respond to exercise treatment. Pre-treatment ERN did not predict treatment response (OR=.74).

Conclusion: Aerobic exercise is effective in alleviating depressive symptoms in adults with major depression, particularly for those with increased depressive symptom severity and larger RewP at baseline. Although aerobic exercise did not modify the RewP or ERN, there is preliminary support for the RewP in predicting who is most likely to respond to exercise as a treatment for depression.