Bodybuilding dogma states that the greater the growth hormone (GH) release after training, the greater the muscle gains. On the surface, this seems to make sense. After all, GH is without a doubt an anabolic hormone, and some studies do suggest it may may play an important role in promoting muscle protein synthesis (MPS) after exercise, which would translate into increased muscle hypertrophy or muscle size gains. But a recent study casts grave doubt on such a notion.
The study consisted of 8 subjects, who completed two separate weight workouts, after which they ingested 25 grams of whey protein.During one workout, they did one-arm biceps curls.Since the extent of GH release during exercise is determined by the mass of muscle being exercised, training a small muscle group,such as the biceps wouldn't be expected to promote any significant GH release. During another workout, they did the same one-arm curls, followed by a heavy leg exercise. Adding this large muscle group exercise would be expected to promote a higher GH release. Biopsies or bits of muscle tissue were extrracted from the exercised and the not exercised arm to check the extent of MPS and also the response to muscle anabolic signaling pathways.
Within 15 minutes after the workout that included heavy leg work, serum GH levels elevated by 684% above baseline; IGF-1 levels rose by 35%. After 30 minutes, GH levels were still 281% higher than baseline. But indicators of MPS didn't differ between the small muscle and large muscle workout. Based on this, the study authors concluded that."Elevated physiological levels of GH and IGF-1, in response to resistance exercise, do not provide any additive effect, and are likely not involved in [muscle] hypertrophy."
De Lisio M, et al. No impact of acute resistance exercise-induced elevation of growth hormone on JAK/STAT signaling or mixed muscle protein synthesis in young men.Appl Physiol Nutr Metab2009;34:1125.
