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Epinephrine, or adrenaline, is a hormone secreted by the adrenal glands. Part of the body's "fight or flight" response, adrenaline is released during periods of stress on the body. Adrenaline does play a role in exercise physiology, and even the thought of exercise can stimulate an adrenaline rush.

Adrenaline Physiology

The body's sympathetic nervous system controls the release of adrenaline. Any stress on the body, such as fear, anger or physical exertion, can stimulate brain cells in the nervous system to initiate the "fight or flight" pathway. Stimulated brain cells signal the adrenal glands, which are endocrine organs located above the kidneys, to release adrenaline. In the bloodstream, adrenaline acts as a hormone, signaling muscles and other tissue in the "flight or fight" response.

Physical Effects of Adrenaline

Adrenaline improves athletic performance and heightens the body's senses. It dilates the pupils and increases sweating. By increasing heart rate, increasing blood pressure and constricting the arteries, adrenaline improves oxygen flow to muscle tissue. Increasing oxygen to muscle cells strengthens the tissue and improves muscle endurance. Adrenaline can open the airways for better breathing and redirect blood flow to vital organs, where oxygen supply proves imperative.

Emotional Effects of Adrenaline

Before, during and after exercising, athletes experience an emotional euphoria known as "runner's high." An adrenaline rush triggers many responses throughout the body, including the release of neurotransmitters. Triggered by the cascade of events after an adrenaline rush, neurotransmitters called endorphins evoke an uplifting emotional response within the brain temporarily, and help fight off the ill effects of stress. Doctors prescribe exercise to combat depression and stress because of the emotional balance that adrenaline rushes provide.

Biochemical Effects of Adrenaline

Epinephrine stimulates hormonal responses in the body and affects the metabolism. Adrenaline facilitates the breakdown of sugar and fat. The body stores fat and sugars, called carbohydrates, for energy. During physical exertion, the body depletes its initial energy supply and taps into the stored energy in carbs and fats. The adrenaline rush is part of the pathway for this metabolic activity.

Artificial Adrenaline Rush

Adrenaline rushes prove medically significant, as epinephrine is occasionally used as a drug treatment. By injecting large concentrations of epinephrine into the bloodstream, doctors create an artificial adrenaline rush to increase heart strength and redirect oxygen flow to vital organs. Adrenaline rushes can be life savers during cardiac arrest, anaphylactic shock or asthma attacks. Some athletes use adrenaline injections to enhance their physical performance, but inducing an artificial adrenaline rush with no medical emergency can be deadly. Herbal supplements for epinephrine can cause side effects such as dizziness and headaches.