Most of us will be spending Thanksgiving with (for better or worse) our family members. Instead of letting them get the best of you...read on.

By Gretchen Reynolds

For years,researchers have known that exercise can affect certain moods. Running, bike riding and other exercise programs have repeatedly been found to combat clinical depression. Similarly, a study from Germany published in April found that light-duty activity like walking or gardening made participants "happy," in the estimation of the scientists. Even laboratory rats and mice respond emotionally to exercise; although their precise "moods" are hard to parse, their behavior indicates that exercise makes them more relaxed and confident.

But what about anger, one of the more universal and, in its way, destructive moods? Can exercise influence how angry you become in certain situations?

A study presented at the most recent annual conference of the American College of Sports Medicine provides some provocative if ambiguous answers. For the study, hundreds of undergraduates at the University of Georgia filled out questionnaires about their moods. From that group, researchers chose 16 young men with "high trait anger" or, in less technical terms, a very short fuse. They were, their questionnaires indicated, habitually touchy.

The researchers invited the men to a lab and had them fill out a survey about their moods at that moment. During the two days of the study, the men were each fitted with high-tech hairnets containing multiple sensors that could read electrical activity in the brain. Next, researchers flashed a series of slides across viewing screens set up in front of each young man. The slides, intended to induce anger, depicted upsetting events like Ku Klux Klan rallies and children under fire from soldiers, which were interspersed with more pleasant images. Electrical activity in the men's brains indicated that they were growing angry during the display. For confirmation, they described to researchers how angry they felt, using a numerical scale from 0 to 9.

On alternate days, after viewing the slides again (though always in a different order), the men either sat quietly or rode a stationary bike for 30 minutes at a moderate pace while their brain patterns and verbal estimations of anger were recorded. Afterward, the researchers examined how angry the volunteers became during each session.

The results showed that when the volunteers hadn't exercised, their second viewing of the slides aroused significantly more anger than the first. After exercise, conversely, the men's anger reached a plateau. They still became upset during the slide show - exercise didn't inure them to what they saw - but the exercise allowed them to end the session no angrier than they began it.

What the results of the study suggest is that "exercise, even a single bout of it, can have a robust prophylactic effect" against the buildup of anger, said Nathaniel Thom, a stress physiologist who was the study's lead researcher.

"It's like taking aspirin to combat heart disease," he said. "You reduce your risk."

When the men did not exercise, they had considerable difficulty controlling their racing emotion. But after exercise, they handled what they saw with more aplomb. Their moods were under firmer control.

The question of just how, physiologically, exercise blunts anger remains open. Mr. Thom and his colleagues did not test levels of stress hormones or brain chemicals in the test subjects. But earlier work by other scientists suggests that serotonin, a neurotransmitter in the brain, probably played a role, Mr. Thom said. "Animal studies have found that low levels of serotonin are associated with aggression, which is our best analogue of anger in animals," he said. "Exercise increases serotonin levels in the rat brain." Low serotonin levels in humans are also thought to contribute to mood disorders.

Changes in the activity of certain genes within the brain may also have an impact. In a 2007 experiment at Yale University, researchers found that prolonged running altered the expression of almost three dozen genes associated with mood in the brains of laboratory mice. Mr. Thom says he hopes that future studies by himself and others will help to determine the specific underlying mechanisms that link exercise and a reduction of anger.