Physical Activity & Depression
Individuals who are physically active are less likely to be depressed. It is not clear if this effect is due to the physical, physiological or psychological effects of exercise. It is possible that all of these factors contribute to the effect. Most psychiatrists now commonly prescribe physical activity for many of their depressed patients.
This slide shows the relationship between levels of physical activity and clinically diagnosted depression (CES-D Scores of 16 or more).
See Brown et al., Medicine and Science in Sports and Exercise, 1996 for more details.