Hormones and Endurance

In the course of training, the normal physical, chemical, and mental stresses have significant influence on athletic performance and overall health. While many factors are associated with this, the hormonal system plays a major role by responding to stress. Some of these hormones are briefly discussed here and elsewhere throughout this book.

A variety of important hormones are produced throughout the body. A number of very important ones are made by the adrenal glands (two small glands atop our kidneys) using cholesterol as a building block to their production. These hormones are important for success in all sports. Cortisol and DHEA (dehydroepiandrosterone) are among the more than fifty hormones produced by the adrenal glands. Three classes of hormones are particularly important for endurance: glucocorticoids, mineralocorticoids, and androgens.

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Glucocorticoids increase liver glycogen and promote fat and protein metabolism. Cortisol is a key glucocorticoid, and is considered one of the main stress hormones—while a moderate amount is necessary, higher levels can wreck our endurance. Cortisol is elevated more significantly with anaerobic training, competition, and in overtraining (although long-term overtraining can result in cortisol depletion, along with the depletion of many other hormone levels). Too much cortisol can disturb normal blood sugar regulation and cause the body to store fat (especially in the face or abdomen).

Too much training or competitive stress—or too much of any type of stress we encounter in our lives—can produce high cortisol levels. In women, this may cause amenorrhea (the loss of a menstrual cycle) and bone loss. In men, high cortisol can adversely impact reproductive status and muscle mass due to lowered testosterone.

Too much cortisol can also reduce the output of other adrenal hormones, including the mineralocorticoids. Aldosterone is an example. This hormone regulates the balance of water and electrolytes (the minerals calcium, magnesium, sodium, and potassium).

The most common androgen is DHEA, which makes the sex hormones testosterone and estrogen in both men and women. Testosterone is important for muscles and bones, and overall recovery. In postmenopausal women, adrenal estrogen production occurs to compensate for the ovaries not producing any more estrogen.

The adrenal glands also produce another pair of hormones called epinephrine and norepinephrine. These are important for the “fight or flight” mechanism and glycogen regulation, and they control heart rate, respiration, blood flow, and various aspects of metabolism. In all, these hormones are regulated by the stress we put on our bodies, and by the brain.

Two important hormones produced in the pancreas—insulin and glucagon—are also important for endurance athletes. Any condition that affects these hormones—most notably the quality of the diet—can significantly affect the burning of fat and sugar for energy. For example, a high-carbohydrate diet increases insulin production even in relatively healthy athletes, which can reduce fat burning. High cortisol can also increase insulin levels, as can overtraining, other stresses, or certain drugs such as birth control pills. In turn, high levels of insulin are associated with low DHEA production. With the onset of exercise, glucagon normally increases, and insulin diminishes, a combo that helps regulate glucose and glycogen, and increase fat burning.