Aerobic Exercise & Hormones

Exercise causes various glands within your body to produce higher concentrations of hormones. Many different hormones are produced when exercising, and the concentrations and effects of each vary with both training duration and intensity. The harder and longer you train, the greater the response, and this is not always beneficial. Consult your physician before beginning any diet or exercise program.

Human Growth Hormone

Human growth hormone is secreted by the pancreas in response to the need for energy while exercising. While growth hormone can assist in protein synthesis, or the ability to build muscle, while performing aerobic exercise it helps you metabolize fat for energy. Your body will preferentially burn sugars, but higher levels of growth hormone allow more fat to be utilized for energy. The release of growth hormone is increased by both the duration and intensity of exercise, but intensity is a much larger factor.

Thyroxine

Thyroxine is a hormone produced by the thyroid gland known as T4. Thyroxine raises the metabolic rate of the majority of cells within your body, causing an increase in calories burned. Thyroxine is an important hormone in fat loss and metabolism, and the longer you exercise, the more thyroxine you will release. The more intensely you exercise, the longer your thyroxine levels will remain elevated. While it is difficult to train both long and hard, interval training can simulate this.

Epinephrine

Epinephrine, or adrenaline, is a hormone produced by the adrenal glands. This hormone increases the amount of blood pumped by the heart secondary to the "fight or flight" response. To do so, fat is stimulated and broken down for fuel, as well as stored glycogen, or sugar. Epinephrine does not discriminate, it will scavenge anything, and if you are lacking in available fat and glycogen stores, it will cannibalize muscle tissue. Epinephrine production is directly proportional to exercise intensity and duration.

Insulin

Insulin is produced by the pancreas and functions to metabolize sugar for energy. Insulin also helps to store energy by shuttling amino acids and glycogen into cells, as well as fat. Following a workout where your glycogen levels are depleted and your insulin levels are high is the ideal time to consume a shake consisting of simple sugars like dextrose or glucose, as almost all of it will wind up in your muscles. At any other time, the insulin response will cause these sugars to be stored as fat.

Cortisol

Cortisol is a steroidal hormone produced by the adrenal glands, and the production of cortisol is directly proportional to exercise duration. It is produced by stress, and its primary function is to increase blood sugar. While it can aid in fat, protein and carbohydrate metabolism, cortisol will also scavenge muscle tissue to supply energy, and can promote fat storage when levels are extremely high. The cortisol response to stress is to attempt to store energy, and your body will respond by storing energy as fat.