Why do some athletes use human growth hormones?

Human growth hormone (HGH), Insulin-Like Growth Factor (IGF-1) and insulin may stimulate muscle and bone development, in addition to breaking down fat.

HGH helps children grow and develop normally. Adults who take artificial HGH experience increased muscle mass, bone mass and bone strength. HGH also helps break down fat cells, leading to easier weight control. Some athletes are especially fond of HGH because it's very hard to detect. However, its side effects include acromegaly, enlarged internal organs and heart problems.

IGF-1 increases HGH's effectiveness. Like HGH, IGF-1 increases muscle mass and bone mass, and it also breaks down fat. However, IGF-1 can cause hypoglycemia. Insulin is a hormone normally produced by the body. If insulin is combined with HGH or other steroids, it can stimulate muscle development. As with IGF-1, insulin can cause hypoglycemia, which can be associated with shaking, nausea and weakness. Extreme hypoglycemia can induce a coma, and can even cause death.Human growth hormone (HGH), Insulin-Like Growth Factor (IGF-1) and insulin may stimulate muscle and bone development, in addition to breaking down fat.

HGH helps children grow and develop normally. Adults who take artificial HGH experience increased muscle mass, bone mass and bone strength. HGH also helps break down fat cells, leading to easier weight control. Some athletes are especially fond of HGH because it's very hard to detect. However, its side effects include acromegaly, enlarged internal organs and heart problems.

IGF-1 increases HGH's effectiveness. Like HGH, IGF-1 increases muscle mass and bone mass, and it also breaks down fat. However, IGF-1 can cause hypoglycemia. Insulin is a hormone normally produced by the body. If insulin is combined with HGH or other steroids, it can stimulate muscle development. As with IGF-1, insulin can cause hypoglycemia, which can be associated with shaking, nausea and weakness. Extreme hypoglycemia can induce a coma, and can even cause death.

Growth hormone and exercise:
The effect of acute exercise on production of HGH in the body has been widely described in the literature. The concentration of HGH in blood increases with time for a given work intensity and can increase 10‐fold during prolonged moderate exercise. During more intensive exercise (with accumulation of lactate at 70% Vo2 max for a short term period such as 10–20 minutes) HGH will increase by 5–10‐fold. With short exercise durations, levels of GH will generally peak at 15–30 minutes after the exercise. Furthermore, it appears that hGH response is more closely related to the peak intensity of exercise than the total work output. Endurance training generally amplifies the pulsate release of growth hormone, elevating the GH amplitude. This appears evident when the training is very hard and above the aerobic threshold.

Apart from exercise related increase, hGH secretion can be affected by other factors—for example, GH secretion is increased in hypoglycaemia, increased temperature, and stress, whereas it decreases in obesity, or with a carbohydrate‐rich diet and intake of β2 adrenergic agonists. Thus, it is hard to differentiate between the physiological increase in HGH levels seen in exercise and what can be from external HGH administration (as in doping). This problem makes the purely quantitative approach of measuring directly the total circulating GH not feasible in case of doping, except if the conditions of collection of biological samples are well controlled.