Growth hormone (GH)

Growth hormone (GH) is a hormone produced in the anterior pituitary gland, with roles in protein synthesis, tissue growth and fat use.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 93.},^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 94.} The NSCA describes GH as a family of molecules: most studies measure the 22 kDa form, but many other forms circulate in the blood.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 93.} Its effects include increased protein synthesis, fat breakdown, fatty acid use, collagen synthesis and cartilage growth.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 94.}

The 22 kDa form is released in bursts that peak at night during sleep; exercise appears to increase their size and number.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 94.} A drop in pH and a rise in lactate are substantial triggers for this form of GH, linking its response to glycolytic work.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 94.},^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 95.}

In practice

• Shorter rest intervals produce higher serum GH than longer rests with similar total work.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 95.} Three sets of 10RM with 1-minute rests brought large increases, while 5RM loads with 3-minute rests did not raise GH above resting levels in women.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 95.}
• A light load with many reps (28% of 7RM) produced no change, suggesting a minimum intensity is required.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 94.},^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 95.}
• Sleep, nutrition, alcohol, age and sex all alter GH release patterns.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 94.}

Does a GH increase mean more muscle growth?

The NSCA calls GH one of the most potent anabolic hormones, but cautions that a link between the GH response and muscle fiber growth doesn’t prove cause and effect.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 94.} Rippetoe argues that GH’s anabolic role is mainly in growing children, that elevated levels in adults probably manage fuel use, and that GH has not been shown to raise lean mass in adults.^{4Rippetoe et al., Practical Programming for Strength Training, 3rd ed., p. 98.} Schoenfeld describes the role of acute hormone elevations in hypertrophy as unclear and likely minor.^{5Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 32.}