While human intellect has developed rapidly since our species first walked upright, the physiological mechanisms that maintain our survival have evolved comparatively little. Unfortunately, the body's traditional fight-or-flight response to stressful situations seldom offers the best way to deal with the problems we encounter daily.
The bulk of today's stress
is cognitive--not physical--in origin. Yet the body is still reacting as it was millennia ago when physical attack was high on the list of concerns. When the stress response overstays its welcome--as it often does with our work-related worries that never seem to go away--unhealthy and often chronic stress results.
The physical and emotional manifestations of the stress response, such as increased heart rate, blood pressure, blood sugar levels and muscle tension are designed to dissipate when an immediate physical threat is over. When stress stays on because of the complex set of our worries, they can turn against the body. Over time, the hormones causing these responses may wind up causing heart disease, hypertension, suppressed immunity, colitis, irritable bowel syndrome and even depression.
In a life-threatening situation, the body shuts down all non-vital functioning to better mobilize its fight-or-flee response. This includes digestion, which during prolonged periods of stress can lead to gastrointestinal disorders. The reason stress causes ulcers, for example, is that the body has ceased producing the mucus that protects the stomach during digestion, when hydrochloric acid is secreted to help break down food.
The body knows that we won't be stopping for a meal during a fight or a narrow escape from a predator. But the sources of stress today do not cause us to actually fight or flee, and so we find ourselves stressed, but nevertheless eating. This results in the production of digestive acid without the protective mucus. An ulcer results. Our bodies cannot distinguish between life threats and more common sources of stress such as traffic jams and marital spats.
There is a sound scientific basis, then, for the effectiveness of regular exercise on stress relief. Since the fight-or-flight response is designed for physical action, exercise is a great way of dissipating the physical manifestations of stress hormones in the body. Exercise, even regular stretching, can relieve tension in the muscles. While fight-or-flight mode often taxes the immune system by preparing it for physiological warfare against an outside force, studies show that moderate physical activity can bolster the immune response.
Exercise can also counteract the anxiety that stress hormones such as adrenaline and cortisol may cause when in the bloodstream for prolonged periods. Exercise also uses up the excess adrenaline, and has been shown to blunt cortisol production. But another way it achieves this is by releasing serotonin, a neurotransmitter that stimulates the brain's "happy centers." This occurs most dramatically within the first 30 minutes of physical activity, then tapers off. Exercise also induces the release of endorphins, which block pain messages. The result is mood enhancement.
Finally, there are peripheral benefits to physical activity. The self-confidence that comes with weight loss and improved body
image affects our outlook, and so our interactions with others, which in turn further improve our mood.