Research published in the May, 2006 issue of Family Practice News studied 80 adults with mild to moderate depression. The subjects were placed randomly into one of five groups. Two of the groups did very low levels of exercise; one for three days per week and another for five days per week (7 kcal/kg/wk). Two other groups exercised aerobically at a higher level (17.5 kcal/kg/wk)—over twice the level of the first two groups. One of these groups exercised three times each week, and the other exercised five times each week. The control group did stretching, but no aerobic activity.

The study lasted 12 weeks. None of the subjects were taking antidepressant medication. Their depression was rated on the Hamilton Rating Scale for Depression (HAM-D). Symptoms dropped by 47% in the groups doing the higher amount of exercise, compared to 30% in the light exercise group. In the control group, depression scores dropped by 29% at the end of the 12 weeks (although the controls had more subjects drop out of the study than the other four groups combined).

Subjects were considered to have a positive response to treatment if their HAM-D scores reduced by 50% or more. This occurred in 46% of the groups doing the higher levels of exercise, and only 26% of those doing light exercise experienced this level of improvement. Only 15% of the controls had their scores reduced by 50% or more.

Subjects were considered to be in remission if their HAM-D scores were seven or less. In the groups doing the higher level of exercise, 42% of them were considered to be in remission, compared to 26% in the low level exercise groups and 11% of the controls. The authors found the rate of remission in the high-level exercise group to be comparable to other forms of treatment for depression.