Human growth hormone is secreted by the anterior lobe of the pituitary gland. It plays a role in bone density, muscle mass, fat mass and exercise capacity, according to the Mayo Clinic. As you age, the pituitary gland slowly starts to produce less of the growth hormone, resulting in a decrease in muscle mass and bone density, and an increase in fat mass. However, growth hormone can be naturally stimulated through weight training, aerobic exercise, proper nutrition and rest.
Weight training helps to stimulate the pituitary gland to release the growth hormone to promote muscle growth and hypertrophy, as well as stimulates the body to metabolize fat. When muscles contract and relax during multiple sets of weight training, the body produces significant levels of growth hormone to repair and renew the tissues that have been placed under optimal stress, according to BodybuildingForYou.com.
Growth hormone levels elevate during aerobic exercise in proportion to the exercise intensity and remain elevated for some time after exercise, according to Jack H. Wilmore and David L. Costill, authors of the "Physiology of Sport and Exercise." Performing at least 30 minutes of aerobic exercise five days a week at moderate to high intensity will trigger the release of growth hormone. Though an increased intensity level will stimulate the release of the hormone, overtraining will cause it not to release.
For muscle growth to occur, amino acids must be present in the body. Amino acids found in protein help to repair and build muscle tissue. Consuming a well-balanced diet consisting of at least 30 percent of your total daily calories in protein is enough to effectively promote muscle growth. Protein sources can come from either plant or animal sources. However, when choosing animal sources, it is best to eat lean meats such as chicken breast, lean beef, fish, eggs or low-fat dairy products.
Lack of sleep or overtraining will have the opposite effect on the human growth hormone. When the body does not receive enough sleep or is overtrained, the adrenal gland releases the stress hormone cortisol, which causes your body to store more fat. For your body to produce the growth hormone, adequate sleep -- between seven and nine hours -- is necessary to stimulate muscle growth as a result of weight training.