Growth Hormone Stimulates Collagen Synthesis, But Not Protein Synthesis
By Robbie Durand, M.A.
Senior Science Editor
“GROWTH HORMONE IS NO MUSCLE BUILDER.” This headline appeared in many newspapers and newswires in the last few months. The controversy was based on a study that recently appeared on the science blogs— making news headlines. A recent meta-analysis (a collection of previous research findings) published in the Annals of Internal Medicine reported that growth hormone (GH) has little benefit for building muscle or improving quality of life. The article explained that while GH has been reported to build muscle and reduce body fat, the research does not support GH as a muscle builder. The meta-analysis also noted that GH causes a host of unhealthy side effects including joint pain, soft tissue swelling, carpal tunnel syndrome, and a heightened risk of diabetes.
The article did acknowledge that GH administration increased lean muscle mass by more than 2 kilograms (4 pounds), and decreased fat mass by roughly the same amount— but noted that the side effects associated with GH usage were not worth the small changes in body composition. The lead author also claimed that the small increases in lean mass could easily be accomplished by a heavy resistance exercise program; he basically stated you’re paying big bucks for a small investment in muscle growth. So is GH as worthless for building muscle as the media has claimed?
[b]GH]
If you are not familiar with the story of “The Emperor’s New Clothes,” it’s an interesting fable. An Emperor who only cares about his wardrobe hires swindlers who promise him the “grandest wardrobe he ever wore.” The tailors tell him the wardrobe consists of clothes made from a fabric that is invisible to anyone who is unfit for his position or “just hopelessly stupid.” The Emperor cannot see the clothes himself, but pretends that he can— for fear of appearing unfit for his position or stupid; his ministers do the same.
When the swindlers report that his suit is finished, the Emperor marches in procession before his subjects. A child in the crowd calls out that the Emperor is wearing nothing at all, and the cry is taken up by others. The Emperor cringes, suspecting the assertion is true, but holds himself up proudly and continues the procession. Much like the Emperor and his invisible clothing, bodybuilders are still taking GH— thinking it’s a muscle builder when in fact there is little evidence that GH can increase muscle mass.
Previous research has shown that GH administration has no effect on human muscle size and muscle protein synthesis. Other studies reported that GH did not stimulate muscle protein synthesis. Interestingly, many athletes may “feel” like they are bigger while on GH— because of the perception of increased water retention and possibly increased muscle stiffness due to growth of collagen tissue. This month’s Journal of Physiology made my draw drop after I read their latest article on how GH affects muscle and collagen protein synthesis.
Growing Collagen, Not Muscle!
Researchers from Denmark performed a randomized, double-blinded, placebo-controlled crossover trial in which sedentary subjects were supplemented with recombinant human GH (rhGH) initially (1-7 days) at 33.3 ?g kg per day, and at 50 ?g kg per day for the latter half (8-14 days) of the experimental period. Subjects performed a bout of leg extension exercises, which consisted of 10 sets of 10 reps at 70 percent of their 1RM. Subjects returned to the laboratory and underwent markers of protein synthesis for tendon and muscle collagen proteins and muscle protein synthesis at 24 hours post-exercise.
At the end of the study, a corresponding increase in systemic IGF-1 and IGFBP-3 occurred with rhGH supplementation, whereas there were no changes in systemic GH or associated blood indices in the placebo condition. Tendon collagen I mRNA expression and tendon collagen protein synthesis increased by 3.9-fold and 1.3-fold, respectively, and muscle collagen I mRNA expression and muscle collagen protein synthesis increased by 2.3-fold and 5.8-fold, respectively.
Myofibrillar protein synthesis was unaffected by elevation of GH and IGF-1. So basically, GH increased serum IGF-1 levels; but there were increases in collagen and tendon protein synthesis, but no increase in muscle protein synthesis.
The study found that circulating and local IGF-1 increased threefold, and there were no increases in muscle protein synthesis. This is great news for muscle strength athletes, given that stronger tendons and collagen are going to enhance muscle strength. GH did not do anything directly to muscle— unlike testosterone, which has direct effects of muscle protein synthesis rates.
Based on this study, GH/IGF-1supports the collagen framework around muscle fibers rather than the muscle contractile apparatus per se in adult skeletal muscle. GH/IGF-1 may be more biologically important for strengthening the supportive matrix in tissues than for muscle cell hypertrophy.
Thus, GH/IGF-1 may be important for tissue remodeling for traumatic musculoskeletal injuries in which collagen or tendons are injured. I am not saying that GH is not important, as many studies have reported that low human growth hormone is associated with reduced muscle mass and increased fat mass. However, I see little point in including GH in off-season cycles if you are trying to solely increase muscle mass for the price. On the other hand, maybe the increased collagen strength leads to more resistance that can be handled— which indirectly allows a heavier workload to be utilized and greater tension applied to the muscle— which indirectly, can increase muscle mass.
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