Feeling tired? Wish you had more energy? Got the blues? Studies have shown again and again that regular, moderate exercise reduces stress, increases energy levels and can even fight depression.

In fact, a recent study out of the University of Vermont found that the post-exercise "glow" or general feeling of well-being you get after a workout lasts up to 12 hours. That's a long time! And study authors think that their findings prove that regular exercise can help people feel happier. "This goes a long way to show that even moderate aerobic exercise has the potential to mitigate the daily stress that results in your mood being disturbed," study author Dr. Jeremy Sibold says in an interview.

Here's how it worked: Forty-eight healthy men and women between the ages of 18 and 25 completed a mood survey. Then one group rode stationary bikes for 20 minutes, while the other group didn't exercise at all. Researchers retested mood again at eight hours later, then 12 and 24. The exercisers reported a better mood than the group who didn't exercise -- not a surprise, since that had already been proven in previous studies, but what was a surprise was how long it lasted ... up to 12 hours.

But when you're feeling down, it's sometimes hard to get off the couch in the first place. So here's more good news: You don't have to be a star athlete to reap the mood-boosting rewards of exercise. In fact, just 150 minutes a week -- or five 30-minute sessions -- of moderate exercise (a brisk walk, a low-impact workout DVD, a not-so-leisurely bike ride, you get the idea) can leave you feeling happier and healthier for the rest of the day.

Don't worry if you don't turn into Susie Sunshine overnight -- it can take three to six weeks of consistent exercise to turn your mood around. Just remember that every step you take is a step in the right direction, and bask in that glow of a workout well done.

Have you noticed that regular exercise has an effect on your mood? Share your comments with us.