May 29 (HealthDay News) -- When it comes to boosting your mood, exercise is the gift that keeps on giving and giving, new research suggests.

In fact, the feel-good afterglow a workout brings may last far beyond the hour or so that's been previously assumed.

"Moderate intensity aerobic exercise improves mood immediately and those improvements can last up to 12 hours," concluded study lead researcher Dr. Jeremy Sibold, assistant professor of rehabilitation and movement science at the University of Vermont, Burlington.

The findings were presented this week at the annual meeting of the American College of Sports Medicine in Seattle.

Other studies have found a mood-boosting effect to exercise. But the other research hadn't tracked the effect for as long as Sibold and his team did. "This is one of the few studies that actually looked at a much longer window, 24 hours," he said. "The question I was interested in was, 'How long does that feel-good effect, that improvement, last?'"

To find out, Sibold and co-author Kathy Berg randomly assigned 48 healthy men and women to a control group that did not exercise, or to a group that did exercise. The participants ranged from 18 to 25 years old. At the start of the study, all participants completed a standard survey of mood. The exercisers then rode on a stationary bike for 20 minutes at moderate intensity.

All participants then repeated the mood survey at one, two, four, eight, 12 and 24 hours later.

The mood of the exercisers was better than that of the sedentary group immediately after the workout and for up to 12 hours later, Sibold found.

"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," he said.

Men and women seemed to benefit equally, and the fitness level of the participant didn't seem to matter, the researchers noted.

Experts believe that exercise's mood-boosting effects are partly due to a rise in levels of mood-enhancing neurotransmitters, such as endorphins, in the brain.

The findings point yet again to exercise as a cheap, easily accessible tool against blue moods and even depression, Sibold said. "I think that's really important for the general public to know -- depression is so widespread."

The "dose" of exercise needed to lift mood is not a lot, Sibold said. "We aren't talking about a Lance Armstrong workout." A few minutes a day could pay off, he said.

He urged people to pick an activity they enjoy. Gardening, walking, square dancing or other activities all count, Sibold said.

The American College of Sports Medicine guidelines support the 2008 Physical Activity Guidelines for Americans, which recommend that adults get at least 150 minutes of moderate-intensity physical activity each week. That can be done in five days a week in 30-minute sessions, experts suggest.

The new findings, according to Sibold, should improve the ability of health care professionals to prescribe exercise as a treatment for mood enhancement in healthy people.

The study results came as no surprise to Jennifer Mears, an exercise physiologist and corporate fitness specialist in Colorado Springs, Colo. "There are a lot of other research studies and information out there that would back that up," she said of Sibold's findings.

What is different and noteworthy about his study, she agreed, is the longer follow-up time.

SOURCES: Jeremy Sibold, Ed.D., certified athletic trainer and assistant professor, rehabilitation and movement science, University of Vermont, Burlington; Jennifer Mears, exercise physiologist and corporate fitness specialist, Colorado Springs, Colo.; presentation, May 27, 2009, 56th annual meeting, American College of Sports Medicine, Seattle