Wednesday, December 28, 2011

Why exercise makes us feel good

Why exercise makes us feel good

http://www.theweek.co.om/disCon.aspx?Cval=5598

Why does exercise make us happy and calm? Almost everyone agrees that it generally does, a conclusion supported by research. A survey by Norwegian researchers published this month, for instance, found that those who engaged in any exercise, even a small amount, reported improved mental health compared with Norwegians who, despite the tempting nearness of mountains and fjords, never got out and exercised.

A separate study, presented last month at the annual meeting of the American College of Sports Medicine, showed that six weeks of bicycle riding or weight training eased symptoms in women who’d received a diagnosis of anxiety disorder. The weight training was especially effective at reducing feelings of irritability, perhaps because the women felt capable now of pounding whomever or whatever was irritating them.

But just how, at a deep, cellular level, exercise affects anxiety and other moods has been difficult to pin down. The brain is physically inaccessible and complex. But a recent animal study from researchers at the National Institute of Mental Health provides some intriguing new clues into how exercise intertwines with emotions, along with the soothing message that it may not require much physical activity to provide lasting emotional resilience.

For the experiment, researchers at the institute gathered two types of male mice. Some were strong and aggressive; the others were less so. The alpha mice got private cages. Male mice in the wild are territorial loners. So when the punier mice were later slipped into the same cages as the aggressive ones, separa-ted only by a clear partition, the big mice acted like thugs. They emplo-yed every animal intimidation technique and, during daily, five-minute periods when the partition was removed, had to be restrained from harming the smaller mice, which, in the face of such treatment, became predictably twitchy and submissive.

After two weeks of cohabitation, many of these weaker mice were nervous wrecks. When the researc-hers tested them in a series of stressful situations away from the cages, the mice responded with, as the scientists call it, ‘anxiety-like behaviour’. They froze or ran for dark corners. Everything upset them. “We don’t use words like ‘depressed’ to describe the animals’ condition,” said Michael L Lehmann, a postdoctoral fellow at the institute and lead author of the study. But in effect, those mice had responded to the repeated stress by becoming depressed.

But that was not true for a subgroup of mice that had been allowed access to running wheels and nifty, explorable tubes in their cages for several weeks before they were housed with the aggressive mice. These mice, although wisely submissive when confronted by the bullies, rallied nicely when away from them. They didn’t freeze or cling to dark spaces in unfamiliar situations. They explored. They appeared to be, Michael said, ‘stress-resistant’.

“In people, we know that repeated applications of stress can lead to anxiety disorders and depression,” Mic-hael said. “But one of the mysteries of mental illness is why some people respond pathologically to stress and some seem to be stress-resistant.” To discern what was different, physiologically, about the stress-resistant mice, the scientists looked at brain cells using stains and other techniques.

They determined that neurons in part of the rodents’ medial prefrontal cortex, an area of the brain involved in emotional processing in animals and people, had been firing often and rapidly in recent weeks, as had neurons in other linked parts of the brain, including the amygdala, which is known to handle feelings of fear and anxiety.

The animals that had not run before moving in with the mean mice showed much less neuronal activity in these portions of the brain. Michael said that he believed that the running was key to the exercised animals’ ability to bounce back from their unpleasant housing conditions.

Of course, as we all know, mice are not people. But the scientists believe that this particular experiment is a fair representation of human interpersonal relations. Hierarchies, mar-ked by bullying and resulting stress, are found among people all the time.

Perhaps best of all, Michael does not believe that hours of daily exercise are needed or desirable to achieve emotional resilience. The mice in his lab ran only when and for as long as they wished, over the course of several weeks. Other animal experiments have intimated that too much exercise could contribute to anxiety, and Michael agrees that that outcome is possible.

Moderate levels of exercise seem to provide the most stress-relieving benefits, he said. Michael does not have a car and walks everywhere, and although he lives in Washington, a cauldron of stress induction, he describes himself as a ‘pretty calm guy.

© 2011 The New York Times News Service

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