Most runners would know that getting of your arse does more for you than making it smaller, it has an incredible effect on mood and stress.
One of my main motivators in starting was to deal with this, I was working as a Team Leader of Psychologists and Social Workers at a major Sydney Hospital and was getting bigger and lazier as I went on....the more i put into it the more it took out of me........
It seems that science also demonstrates the mental health benefits of running according to a recent article in USA Today (here)
Now, data pooled from many small studies suggest that in people diagnosed with depression or anxiety, the immediate mood boost is followed by longer-term relief, similar to that offered by medication and talk therapy, says Daniel Landers, a professor emeritus in the department of kinesiology at Arizona State University.
And exercise seems to work better than relaxation, meditation, stress education and music therapy, Landers says.
"Most physicians and therapists are aware of the effects," says Chad Rethorst, a researcher at the University of Texas Southwestern Medical Center in Dallas. "But they may not be comfortable prescribing it."