Fight-or-flight response tied to fitness

Jun 28 2014, 15:57 IST
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For some time, scientists and exercise experts have debated the merits of intensity in exercise. For some time, scientists and exercise experts have debated the merits of intensity in exercise.
SummaryStrenuous exercise acts as a kind of stress, prompting the fight or flight response, which in turn, sends the cardiovascular system into high gear.

Intense exercise changes the body and muscles at a molecular level in ways that milder physical activity doesnít match, according to an enlightening new study. Though the study was conducted in mice, the findings add to growing scientific evidence that to realise the greatest benefits from workouts, we probably need to push ourselves.

For some time, scientists and exercise experts have debated the merits of intensity in exercise. Everyone agrees, of course, that any exercise is more healthful than none. But beyond that baseline, is strenuous exercise somehow better, from a physiological standpoint, than a relative stroll?

There have been hints that it may be. Epidemiological studies of walkers, for instance, have found that those whose usual pace is brisk tend to live longer than those who move at a more leisurely rate, even if their overall energy expenditure is similar.

But how intense exercise might uniquely affect the body, especially below the surface at the cellular level, had remained unclear. Thatís where scientists at the Scripps Research Institute in Florida stepped in.

Already, these scientists had been studying the biochemistry of sympathetic nervous system reactions in mice. The sympathetic nervous system is that portion of the autonomic, or involuntary, nervous system that ignites the fight or flight response in animals, including people, when they are faced with peril or stress. In such a situation, the sympathetic nervous system prompts the release of catecholamines, biochemicals such as adrenaline and norepinephrine that set the heart racing, increase alertness and prime the muscles for getaway or battle.

At Scripps, the scientists had been focusing on catecholamines and their relationship with a protein found in both mice and people that is genetically activated during stress, called CRTC2. This protein, they discovered, affects the bodyís use of blood sugar and fatty acids during moments of stress and seems to have an impact on health issues such as insulin resistance.

The researchers also began to wonder about the role of CRTC2 during exercise.

Scientists long have known that the sympathetic nervous system plays a part in exercise, particularly if the activity is intense. Strenuous exercise, the thinking went, acts as a kind of stress, prompting the fight or flight response and the release of catecholamines, which goose the cardiovascular system into high gear. And while these catecholamines were important in helping you to instantly fight or flee, it was generally thought they did not play an important role in the bodyís longer-term

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