Couch potatoes, take heart. You don't have to exercise until you drop to reap mental benefits, according to some research.

Psychologists studying how exercise affects mental health are discovering that how much or how intensely you exercise isnít the key factor in relieving depression and anxiety. In fact, they say that less is more; or at least just as good.

In one study , depressed people used stationary bicycles. Participants' depression declined, even when they weren't biking all that hard.

In another study , people reported how they felt after a 10-minute brisk walk or a 45-minute workout. Those working out for 45 minutes said they were less tense and that their energy at first declined and later rebounded. Those who just walked said that they felt less tense, and they also reported more energy right away.