Running does more than just stress your cardiovascular system and burn fat -- it triggers a strong hormonal response. Like most responses to exercise, the degree of hormonal response depends on both your training intensity and duration. This hormonal response, particularly the increase in thyroid and growth hormone levels, contributes to the amount of fat you burn. Consult a health care practitioner before beginning any exercise program.
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Growth Hormone and Testosterone
Growth hormone is produced by your anterior pituitary gland in response to various stresses. Running is a type of stress that triggers this release. Testosterone is produced by the testes in men, and the ovaries and adrenal glands in women. This hormone works to preserve lean muscle mass, while growth hormone will scavenge fat for fuel. The more intensely you train, the more you trigger the release of these powerful hormones, according to a 2010 study published in "Acta Physiologica Hungarica."
Your thyroid gland produces multiple hormones, including T-3 and T-4, both of which play a role in fat loss. The hormone T-3, in particular, is stimulated by exercise. Prolonged exercise stimulates the production of T-3 to assist with the utilization of both fats and glycogen as fuel, as well as scavenging free-floating fatty acids for energy. Following intense exercise, there is a marked increase in T-3 output from your thyroid gland, according to a 1998 study published in the "Romanian Journal of Physiology."
Epinephrine, or adrenaline, is produced by your adrenal glands in response to a stress or stimulus, such as the "flight or fight" response. Running triggers the fight or flight response. Adrenaline is released in response to the increase in demands for energy. And unlike other hormones, adrenaline will scavenge not only fats and sugars for fuel, but amino acids as well. Like other types of hormones, the increase in adrenaline levels are proportional to increases in exercise intensity, according to a 2007 study published in the "Journal of Strength and Conditioning Research."
Cortisol is another hormone produced by your adrenal glands in response to stress. Cortisol also scavenges anything and everything for fuel. Cortisol is what is known as a "catabolic," or wasting hormone -- its effects are that pronounced. The response of this hormone is also dependent upon your body weight, according to researchers at Islamic Azad University in Tehran who studied the effects of morning and afternoon physical activities on cortisol responses in lean and obese women. The results of this 2011 study showed that the cortisol and stress response was lower later in the day, suggesting that obese women exercise during the afternoon to minimize the stress response that can lead to muscle wasting rather than fat burning.