Your nervous and endocrine systems work together to regulate how your body responds to exercise. When you exercise, the motor neurons, or nerve cells that supply your muscle fibers, increase. When this neural activation occurs, neurotransmitters trigger your endocrine system to release a hormone. In “Exercise Physiology for Health, Fitness and Performance,” Sharon Plowman and Denise Smith explain that the primary role of the hormones released during exercise is to help regulate metabolism, your body’s ability to make and maintain energy.
Exercise increases testosterone, a hormone that is produced in the male testes, the female ovaries and the adrenal glands, which are located just above your kidneys. In “Hormonal Responses to Exercise,” S.K. Powers and Edward T. Howley says this increase in testosterone helps to amplify your lean body mass and strengthen your muscles while simultaneously helping to lower your body fat percentage. Testosterone also boosts sexual libido, improves bone density and augments metabolism.
Human growth hormone, or somatotropin, which is released from the anterior pituitary gland, also increases during exercise. For adults, an increase in hGH helps to mobilize free fatty acids from adipose or connective tissue, and it helps maintain your body’s blood glucose level. In "Exercise and Sport Science," William E. Garrett and Donald T. Kirkendall note that even a short, nine-minute exercise routine can elevate your hGH level. This hormonal elevation then works to stimulate insulin-like growth factor, causing protein synthesis, a process by which your cells generate new proteins.
Garrett and Kirkendall also note that high-intensity exercise sessions, ranging from 20 to 60 minutes, appear to cause small increases the level of an antidiuretic hormone called ADH, which is released from the posterior pituitary. ADH helps to reduce water loss by stimulating water re-absorption by the kidneys. ADH also helps your body to maintain the proper volume of plasma, the liquid portion of your blood. Adequate ADH levels help lower your risk for diabetes insipidus, a disease that results from an ADH deficiency.
Exercise also increases the level of thyroid stimulating hormone -- TSH -- in your blood, note William D. McArdle and Frank I. Katch in “Exercise Physiology: Nutrition, Energy and Human Performance.” They explain that TSH spurs action in your thyroid gland, which produces thyroxine, or T4, and triiodothyronine, or T3. T3 and T4 serve as your body’s internal thermostat. They also help your body maintain a healthy metabolic rate.