Hormones & Exercise

There are many physical, mental, and physiological benefits to regular exercise. One category of benefits is the impact that exercise has on many of your body's hormones. Hormones are chemical messengers within your body that affect almost all aspects of human function:

Growth Hormone

Stimulates protein synthesis (muscle tone/development), and strength of bones, tendons, ligaments, and cartilage - decreases use of glucose and increases use of fat as a fuel during exercise. This helps to reduce body fat and to keep blood glucose at a normal level which helps you to exercise for a longer period of time. Release of growth hormone from the pituitary gland in the brain is increased with increasing aerobic exercise time, especially more intense exercise such as interval training.

Endorphins

An endogenous opioid from the pituitary gland that blocks pain, decreases appetite, creates a feeling of euphoria (the exercise high), and reduces tension and anxiety. Blood levels of endorphins increase up to five times resting levels during longer duration (greater than 30 minutes) aerobic exercise at moderate to intense levels and also during interval training. Also, after several months of regular exercise, you develop an increased sensitivity to endorphins (a higher high from the same level of endorphins), and endorphins that are produced tend to stay in your blood for a longer period of time. This makes longer duration exercise easier (you're feeling no pain) and it causes your exercise high to last for a longer period of time after exercise.

Testosterone

An important hormone in males and females for maintaining muscle tone/volume/strength, increasing basal metabolic rate (metabolism), decreasing body fat, and feeling self-confident. It's produced by the ovaries in females and by the testes in males. Females have only about one tenth the amount of testosterone that males do, but even at that level in females it also plays a role in libido and intensity of orgasms. Production of testosterone in females begins to decline as a woman begins to approach menopause and in males it begins to decline in his forties. Blood levels of testosterone increase with exercise in both males and females beginning about 20 minutes into an exercise session, and blood levels may remain elevated for one to three hours after exercise.

Estrogen

The most biologically active estrogen, 17 beta estradiol, increases fat breakdown from body fat stores so that it can be used and fuel, increases basal metabolic rate (metabolism), elevates your mood, and increases libido. This hormone is at much higher blood levels in females, but the ovaries begin to produce less of it as a woman begins to approach menopause. The amount of 17 beta estradiol secreted by the ovaries increases with exercise, and blood levels may remain elevated for one to four hours after exercise.

Thyroid (T4)

A hormone produced by the thyroid gland, Thyroxine raises the metabolic rate ("metabolism") of almost all cells in the body. This increase in "metabolism" helps you to feel more energetic and also causes you to expend more calories, and thus is important in weight loss. Blood levels of thyroxine increase by about 30% during exercise and remain elevated for several hours afterward — this period of time is increased by an increase in intensity and/or duration of exercise. Regular exercise also increase thyroxine levels at rest.

Epinephrine

A hormone produced primarily by the adrenal medulla that increases the amount of blood the heart pumps and directs blood flow to where it's needed — stimulates breakdown of glycogen (stored carbohydrate) in the active muscles and liver to use as fuel. It also stimulates the breakdown of fat (in stored fat and in active muscles) to use as fuel. The amount of epinephrine released from the adrenal medulla is proportional to the intensity and duration of exercise.

Insulin

An important hormone in regulating (decreasing) blood levels of glucose ("blood sugar") and in directing glucose, fatty acids (fat), and amino acids (protein) into the cells. Insulin secretion by the pancreas is increased in response to a rise in blood sugar and/or amino acids (protein) as is often the case after a meal. Typically, the larger the meal, or the greater the quantity of simple sugars consumed, the larger the insulin response.

An excessive insulin response causes fat production within the cells — thus, insulin is sometimes called the "fat hormone". Many overweight people's cells develop a resistance to insulin so that it takes more insulin to have the same effect. This creates a situation where blood levels of insulin are higher than normal. This condition is often improved by losing weight and daily aerobic exercise. Blood levels of insulin begin to decrease about 10 minutes into an aerobic exercise session and continue to decrease through about 70 minutes of exercise. Regular exercise also increases a cell's sensitivity to insulin at rest.

Glucagon

A hormone that is also secreted by the pancreas, but it's job is to raise blood levels of glucose ("blood sugar"). When blood sugar levels get too low, glucagon is secreted and causes stored carbohydrate (glycogen) in the liver to be released into the blood stream to raise blood sugar to a normal level. It also causes the breakdown of fat so that it can be used as fuel. Glucagon typically begins to be secreted beyond 30 minutes of exercise when blood glucose levels may begin to decrease.

So, next time you're exercising, think about all the wonderful things that are happening to your hormones. It might even make you want to do more exercise!