Physical Exercise and HD
Part 4

Exercise and Stress Alleviation

Exercise may also help the brain to better cope with stress. Stress leads to the release of various neurochemicals and stress hormones. (For more information on stress and its effects on the brain, click here.) Prolonged exposure to stress hormones is detrimental to the health and survival of nerve cells. Normal nerve cells are like miniature trees with a lot of branches. These "branches" are called dendrites. They are structures that connect one nerve cell to many other nerve cells. Stress hormones cause the branches of the dendrites to become shorter and less widespread, such that the affected nerve cell cannot connect to as many nerve cells. With fewer connections, it does not receive as much information as it should, and becomes more prone to injury or death. It is thought that this effect occurs mainly because stress hormones decrease the amount of BDNF in the brain, depriving nerve cells of neurotrophic factors necessary for growth and survival. Exercise directly counteracts this effect by increasing BDNF availability in the brain. As evidence, in a study in which two groups of rats were exposed to stressful stimuli, the effect of exposure to this stress was mediated by exercise. Rats that were able exercise before exposure to the stressful stimuli had normal amounts of BDNF in the brain, whereas rats that were not able to exercise had significantly decreased amounts of BDNF in the brain.

In addition to increasing BDNF availability, exercise also helps regulate the release of harmful stress hormones, so that they don’t flood into the nerve cells and wreak havoc. Researchers first became interested in exploring a possible link between exercise and stress after discovering that physically fit individuals have significantly lowered rates of anxiety and depression. Although popular theory states that exercise causes a rush of endorphins, there is very little evidence for this phenomena. Instead, researchers believe that a chemical known as norepinephrine plays a key role in helping the brain deal with stress more efficiently. During exercise, norephinephrine is released and goes on to directly increase heart rate, release energy from fat, and increase muscle readiness. Studies in animals since the late 1980’s have found that exercise increases concentrations of norepinephrine in regions of the brain involved in the body's stress response. Although the exact mechanism is not known, increased norepinephrine in the brain is thought to decrease the release of other harmful stress chemicals. In fact, some antidepressants work by increasing brain concentrations of norepinephrine.

Many physiologists believe that exercise also enhances the body’s ability to respond to stress in a more general way. Biologically, exercise seems to give the body a chance to practice dealing with stress. It forces the body's physiological systems, all of which are involved in the stress response, to communicate much more closely than usual; e.g. the cardiovascular system communicates with the renal system, which communicates with the muscular system. All are controlled by the central nervous system and sympathetic nervous system, which must also communicate with each other. This "workout" of the body's communication system may be the true value of exercise; the more sedentary we get, the less efficient our bodies become in responding to stress.

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Last Modified: 04/12/2007

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