Stress begins with a physiological response to what your body-mind perceives as life-threatening. For our ancestors, this may have been defending against the aggression of a hungry animal. For modern-day humans, this may be living with the fear of losing a job in a sagging economy, or the health crisis of a family member.

 Whatever the stressor, the mind alerts the body that danger is present. In response, the adrenal glands, located above the kidneys, secrete catecholamine hormones. These adrenaline and noradrenalin hormones act upon the autonomic nervous system, as the body prepares for fight or flight. Heart rate, blood pressure, mental alertness, and muscle tension are increased. The adrenal hormones cause metabolic changes that make energy stores available to each cell and the body begins to sweat. The body also shuts down systems that are not a priority in the immediacy of the moment, including digestion, elimination, growth, repair, and reproduction.

 These adaptive responses have been positive for the survival of the human race over thousands of years. For our ancestors, a stressful situation usually resolved itself quickly. They fought or they ran, and, if they survived, everything returned to normal. The hormones were used beneficially, the adrenal glands stopped producing stress hormones, and systems that were temporarily shut down resumed operation.

To his detriment, modern man is often unable to resolve his stress so directly, and lives chronically stressed as a result. Still responding to the fight or flight response, the adrenals continue to pump stress hormones. The body does not benefit from nutrition because the digestion and elimination systems are slowed down. Even sleep is disturbed by this agitated state.

 In a chronically stressed state, quality of life, and perhaps life itself, is at risk. The body's capacity to heal itself is compromised, either inhibiting recovery from an existing illness or injury, or creating a new one, including high blood pressure, ulcers, back pain, immune dysfunction, reproductive problems, and depression. These conditions add stress of their own and the cycle continues.

(From Relax and Renew: Restful Yoga for Stressful Times, copyright © 1995 by Judith Lasater, Ph.D., P.T. Reprinted with permission from Rodmell Press, Berkeley, Calif., www.rodmellpress.com)