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© 2002

Some readers may recall a two-part article featured in Master Trainer in which I discussed the role of certain anabolic hormones in the adaptation to resistance exercise (1,2). These evidence-based articles essentially discredited the commonly alleged importance of two hormones, growth hormone (GH) and serum insulin-like growth factor-1 (IGF-1), as mediators of the growth response to strength training.

The first article (1) focused specifically on the impact of GH on resistance training effects. I concluded, "GH at normal physiological levels has not conclusively been shown to be a necessity for exercise-induced muscle hypertrophy… Therefore, a training regimen’s design should not be predicated on the acute or chronic behavior of GH."

The follow-up article (2) addressed the role of serum (i.e., circulating) IGF-1 in muscle hypertrophy associated with strength training. In it, I stated, "The premise that circulating IGF-1 greatly influences muscle growth is flawed because circulating IGF-1 does not indicate the level of IGF-1 where it really counts—in skeletal muscle… GH is not important for exercise-induced muscle hypertrophy. Since GH does not directly exert effects on anabolic processes, the anabolic effects must be mediated via circulating IGF-1… [However,] plasma [i.e., circulating] IGF-1 doesn’t appear to exert a strong influence in skeletal muscle adaptation to loading."

Since writing the articles on GH and serum IGF-1 for Master Trainer, I subsequently published another critical article on GH in the popular media (3). This time, however, the main thrust was questioning dietary supplements designed to raise GH levels. The following statements summarize my thoughts on the subject: "Indeed, the effects of GH on body composition changes, particularly lean body mass accretion, have been overstated…" The article continued, "…using GH to increase circulating IGF-1 is an error in judgment. It seems more likely that autocrine IGF-1, which is produced within the muscle itself, is where we should be focusing our attention in our quest to maximize muscle mass… Because GH normally has a half-life of only 20 minutes, supplements to enhance GH output would have to be taken on a very frequent basis throughout the day. Such an approach, however, would likely be inconvenient and cost-prohibitive…"

When one writes against the grain, it always feels good when support comes in the form of independent corroboration. (And, although the truth is not reached by consensus (as Mike Mentzer’s voice echoes), it certainly is nice to know you have intellectual allies.) This corroboration came most recently in the form of a scientific review article published in what is recognized as the second most influential peer-reviewed exercise journal (4), Exercise and Sport Sciences Reviews.

In this very recent publication (5), Hameed, Harridge, and Goldspink explore the effects of GH and especially IGF-1 in the age-related decreases in muscle mass (i.e., sarcopenia) that are characteristic of senescence. The authors present a number of points pertinent to our discussion. For example, the authors indicate that in skeletal muscle IGF-1 levels are independent of GH. Hameed and colleagues find the clinical trials of GH therapy for sarcopenia in older adults to be "disappointing." They go on to state, "The observation that GH seems relatively ineffective in stimulating muscle growth, raises questions as to the role systemic growth factors may play in the adaptation to exercise." The authors summarize, "Although systemic or circulating growth hormone and insulin-like growth factor-1 levels fall as we age, this is likely to be of lesser importance in regard to muscle mass than the role of locally produced insulin-like growth factor-1s generated in the muscle in response to exercise."

Additional points raised in the article by Hameed et al. include elaboration on the likely connection between muscular IGF-1 expression and satellite cell proliferation, supporting the hypothesis that muscle damage initiates the growth response. The authors review encouraging findings that older persons can significantly elevate intramuscular IGF-1 by approximately 500%. This attests to the utility of strength training in the aged and is in agreement with the impressive functional improvements associated with resistance exercise in this population.

Antonio, Chromiak, and Street offer a current review of the dietary supplement literature collected on so-called GH enhancers, or secretagogues (6). The authors elaborate in detail on many human trials of GH secretagogues such as select amino acids. The table provides a list of substances commonly purported to have GH-enhancing properties. Interestingly, the review of Antonio and associates brings to light a number of findings that seem largely incompatible with the use of GH enhancers by weight-trained individuals—who undoubtedly comprise a significant portion of consumers who purchase GH enhancers (along with life extensionists).

First, Antonio and colleagues write, "The GH response to [amino acid supplements] appears to be reduced in exercise-trained individuals." Clearly, this observation undermines the alleged benefits of dietary GH enhancers for strength-trained persons because the exercise-induced GH secretion blunts or masks any effect of dietary GH enhancers.

Second, ingestion of branched-chain amino acids (BCAAs), as noted by the authors, suppresses the expected post-exercise surge in GH concentration. I find this curious because, for quite some time, BCAAs have been a dietary supplement mainstay for bodybuilders and serve important metabolic functions in skeletal muscle; but if BCAAs are allegedly important for exercise-induced muscle growth (as some evidence indicates), then this refutes the idea that GH is absolutely key for muscle hypertrophy.

Third, Antonio et al. note that GH response to secretagogues is greatest in young subjects. But, normal, healthy young persons have ample GH; thus, older persons who do have declining GH levels are less responsive to GH-enhancing stimuli. So, there’s a discrepancy between who exhibits the greatest exercise- or secretagogue-induced GH response (i.e., the young) and who may need it the most (i.e., the old). Does it make any sense that young, normosecretory trainees with naturally surging anabolic hormones would benefit from a relatively mild and transient blip in GH concentration?

Fourth, the authors indicate that a high-protein diet naturally increases resting GH levels and that "the use of specific amino acids to induce GH release may not be effective in strength-trained individuals consuming high-protein." The authors’ thinking, it would appear, is that the high-protein diet would nullify any additional increase in GH by individual amino acids. It is well documented that strength-trained athletes, as well as the average American, consume a relatively high-protein diet (2-3 times above basic needs). Therefore, dietary GH secretagogues would be unlikely to significantly increase GH secretion in most strength-trained persons due to their common consumption of a diet relatively high in protein.

Finally, fasting has been shown to augment GH responsiveness to amino acids and exercise, but fasting is clearly incompatible with a sound diet for athletes. Fasting is known to result in rapid decreases in lean body mass and performance. Clearly, this is antithetical to the goal of increasing muscle mass.

It is worth questioning just how much dietary GH releasers may increase circulating GH. Antonio et al. review a journal article comparing the effects of cycling at 75-90% of maximal oxygen uptake for 20 minutes versus ingesting 30 g of arginine, an amino acid experimentally shown to increase GH levels. The brief bout of exercise increased GH levels beyond that of the horrendously large dose of arginine! The authors review several other articles failing to show an added effect of GH enhancers when used in conjunction with exercise. Regarding resistance exercise, the authors note, "The intensity of the resistance-training workout is positively related to the amplitude of GH release… Exercise is a potent stimulus for GH release and amino acids may not further augment GH release during or after exercise." Perhaps intense exercise is the most potent GH releaser.

Back to my original point, are any of these GH responses of any real importance to resistance-training enthusiasts? Antonio and colleagues (6) offer the following summary on this issue: "No evidence based on properly conducted, rigorous scientific study suggests that the use of amino acid supplements in conjunction with strength training increases muscle growth or lean body mass to a greater extent than strength training alone. Two studies that reported greater increases in body mass and reduction in percent body fat, and gains in total body strength [and] lean body mass… as a result of arginine and ornithine supplementation were seriously flawed."

Over time, scientific opinion is increasingly unsupportive of a critical role for GH and systemic IGF-1 in exercise-induced muscle hypertrophy. Collectively, this evolving consensus casts serious doubt on the importance of nutritional preparations or exercise methodology purported to positively influence these hormones. In my opinion, companies, organizations, or individual "authorities" that continue promoting training strategies, dietary supplements, or even illicit prescription drug use in efforts to increase GH or IGF-1 levels are doing nothing to move bodybuilding science forward. Rather than being on the cutting edge as they would have consumers believe, they are actually retarding individual success by misleading the public. But, science continues to slowly grind onward despite the steadfast purveyors of misinformation.

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References

1. Bradley-Popovich GE. The gland scheme of things: part I. Master Trainer 1999;9(5):12-6.

2. Bradley-Popovich GE. The gland scheme of things: part II. Master Trainer 1999;9(6):18-20.

3. Bradley-Popovich GE. GH=gigantic hype? Anabolic 2001;Issue 3:45-51.

4. Pandolf KB. Editorial. Med Sci Sports Exerc 2002;34:1.

5. Hameed M, Harridge SDR, Goldspink G. Sarcopenia and hypertrophy: a role for insulin-like growth factor-1 in aged muscle? Exerc Sports Sci Rev 2002;30:15-9.

6. Antonio J, Chromiak J, Street C. Androgens and GH releasers. In: Antonio J, Stout J, editors. Sports supplements. Baltimore: Lippincott Williams & Wilkins; 2001. p. 160-78.

Dr. Greg Bradley-Popovich holds master's degrees in Exercise Physiology and Human Nutrition, and he also holds a Doctor of Physical Therapy (DPT) degree. He is a practicing physical therapist and Director of Clinical Research at NW Spine Management, Rehabilitation and Sports Conditioning in Portland, Oregon.

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