It's not easy to make time to work out every day. Gym sessions cut into your work time, family time, snooze time and downtime. But here's some fitness news that will make you smile. A new study in the Journal of Sport & Exercise Psychology found that as little as 15 minutes of physical activity increases levels of feelings like enthusiasm, pride, happiness and excitement. (Think you're too busy? Here are 15 Ways To Find 15 Minutes For Exercise.)

The study tracked the daily activities of 190 college students. They kept a journal logging the amount and level of exercise they got and their overall emotional states. The more physically active people reported greater levels of pleasant feelings, compared to their less-active counterparts, reported the Penn State University researchers. In fact, the participants had higher levels of these feelings on days when they are more physically active than usual. (Plus, a regular workout could land you raise: Discover How Exercise Makes You Smarter.)

Many people lose motivation to keep exercising because they don't see results -- weight loss, better muscle tone, and greater strength -- instantly, explains study author David Conroy. But gaining short-term rewards -- like boosts in mood -- may keep you coming back until you reach your long-term goals, he says.

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Although the study didn't assess how exercise works to lift spirits, the researchers suspect changes in levels of brain chemicals during and after physical activity may be involved. Don't worry: You don't have to be a marathon runner or build the body worthy of a Greek god to get these feel-good benefits. For a quick boost of happiness, you can go for a quick walk around your office building during lunch, or challenge your kids to a snowball fight in the backyard. Or even better try out the routines in The Men's Health Big Book of 15-Minute Workouts and The Women's Health Big Book of 15-Minute Workouts.)

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