How Exercise Affects The Adrenal Gland & Heart Rate

The adrenal glands are located above the kidneys and composed of the inner adrenal medulla and the outer adrenal cortex. The adrenal medulla releases two hormones -- epinephrine and norepinephrine. The adrenal cortex releases many different steroid hormones. The hormones released by the adrenal medulla during exercise have an effect on heart rate.

Adrenal Medulla

When the adrenal medulla is stimulated by the sympathetic nervous system, about 80 percent of its secretion is epinephrine, and 20 percent is norepinephrine, according Jack H. Wilmore and David L. Costill, authors of "The Physiology of Exercise and Sport." These hormones work to together to initiate the fight-or-flight response. The fight-or-flight response helps you handle immediate stress by causing an increase in heart rate, metabolic rate, release of glucose, blood pressure and respiration.

Evidence

A 1999 study at the University of Pennsylvania examined the effects of dynamic resistance exercise -- involving high force and high power -- on the response of the adrenal medulla's hormones in strength-trained men. It found that the adrenal medulla was activated during acute stress from heavy resistance training and remained elevated during longer recovery periods.

Hormone Response

Changes in the plasma levels of epinephrine and norepinephrine change with increased intensity. Norephinephrine levels increase at work rates above 50 percent of maximum oxygen uptake, and epinephrine levels do not increase until exercise intensity exceeds 70 percent of the maximum oxygen uptake, according to Wilmore and Costill. During long-duration exercise, about 60 percent of maximum oxygen uptake, both hormones can be elevated. When exercise ends, epinephrine returns to resting levels within minutes, but norepinephrine can stay elevated for hours.

Fight-or-Flight

The fight-or-flight response associated with the adrenal medulla's hormone release can occur with both physiological and psychological stress. Since most of the stress people experience now is psychological and not physiological, it is important to use exercise to counteract the fight-or-flight response to stress. Physical exercise works to metabolize excessive stress hormones --- restoring your body and mind to a calmer, more relaxed state, according to the Oregon Addictions and Mental Health Services.