Human growth hormone, or hGH, is a substance produced by the pituitary gland in the brain that serves a number of functions in the body, including bone and muscle growth and regulation of metabolic processes. When performed at a sufficient duration and intensity, both aerobic and particularly resistance workouts can trigger the body to secrete more hGH. However, contrary to hGH's reputation as an anabolic agent, there is little evidence that exercise-induced changes in hGH directly support muscle growth or improve physical performance in people with normal hGH levels.
Workouts Promoting Growth Hormone Secretion
According to a 2005 study led by W.J. Kraemer and published in "Sports Medicine," resistance exercise causes the body to release certain hormones including hGH and testosterone, provided that the exercise involves large muscle groups and is performed at a high volume and moderate or high intensity. A 2002 study conducted by the University of North Carolina concluded that both aerobic and and resistance exercise can stimulate hGH secretion if the workout crosses the "lactate threshold," meaning that the exercise is intense enough to cause a buildup of lactate in the blood. However, a 2010 study conducted by Seoul National University researchers and published in the "International Journal of Sport Nutrition and Exercise Metabolism" concluded that workouts involving resistance training increased growth hormone levels in middle-aged women better than did aerobic exercise.
The Sleep Connection
In addition to exercise, sleep is also a significant physiological stimulus for hGH secretion. Individuals with sleep deficiencies experience disrupted hormone secretion levels, particularly of hGH, according to a 2010 paper by Jolanta Orzel-Gryglewska published in "International Journal of Occupational Medicine and Environmental Health." As regular exercise can help promote a healthy sleep cycle, workouts may also, indirectly, guard against hGH disturbances.
Effects of Exercise-Induced hGH Secretion
While hGH plays important roles in human growth and metabolism, there is not evidence to support the theory that exercise-induced changes in hGH levels produce direct anabolic, or muscle-building, effects in healthy individuals, according to a 2010 review published in "The Physician and Sportsmedicine." The review states that despite the belief among bodybuilders that secretion of hGH and testosterone underpins the muscle hypertrophy associated with weight lifting, other mechanisms involved in resistance training are likely responsible for exercise-induced muscle growth. Similarly, a 2010 study published in "Endocrinology and Metabolism Clinics in North America" concluded that while hGH replacement therapy to hGH-deficient individuals provides improvements to some aspects of exercise capacity, there is not sufficient evidence to show hGH enhances athletic performance in people with normal hGH levels.
Growth Hormone Supplement Effects and Safety
Artificially raising hGH status through growth hormone injections is legal only when prescribed by a doctor for a medical condition. Besides being illegal and not producing any demonstrable improvements in athletic performance, abusing hGH for athletic purposes is also dangerous. According to the 2010 "Endocrinology and Metabolism Clinics in North America" study, long-term abuse of hGH may produce symptoms of a metabolic syndrome called acromegaly which is associated with increased morbidity and mortality. It is also important to note that while many websites sell "growth hormone" supplements, these products are likely fake and potentially dangerous.
References
- PubMed.gov: Hormonal Responses and Adaptations to Resistance Exercise and Training
- PubMed.gov: The Exercise-Induced Growth Hormone Response in Athletes
- PubMed.gov: Growth Hormone Release During Acute and Chronic Aerobic and Resistance Exercise: Recent Findings
- PubMed.gov: 12 Weeks of Combined Exercise is Better than Aerobic Exercise for Increasing Growth Hormone in Middle Aged Women
- PubMed.gov: Consequences of Sleep Deprivation
- PubMed.gov: Growth Hormone and Atheltic Performance: Is it Safe and Effective for Athletic Performance
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