Human Growth Hormone- Part II: Does it enhance physical performance?
Quick Hit Summary
HGH injections are a hot topic in both the athletic and anti-aging communities. However, there is little scientific evidence to support the notion that HGH alone will provide much benefit for either group. Currently there is no evidence that HGH alone will increase strength, vertical jump, or aerobic capacity (VO2) in trained or untrained athletes. However, it does appear to increase anaerobic capacity in recreational strength athletes. These effects appear to be amplified when co-administered with testosterone. A similar lack of effect with HGH alone has been seen in older individuals. HGH does appear to have a strong anabolic effect on collagen, the main protein in connective tissue (tendons, cartilage, ligaments). Increased fat loss has also been observed in those receiving HGH. Adverse affects were reported in all the studies that examined HGH administration. Most common side effects were joint pain, edema, and carpel tunnel.
HGH Injections
In the first part of this article, we observed a lack of evidence supporting the use of popular amino acids purported to stimulate HGH secretion. Furthermore, it was noted that exercise induced HGH secretions failed to enhance myofibrillar protein synthesis (MPS) (the proteins which are responsible for generating force in the muscle during muscular contraction), muscle strength, and/or muscle size. I know what you’re thinking right now… The studies reviewed in Part I of this article examined the effects of exercise induced or HGH secretagogues on increases in HGH. Individuals who take HGH injections to increase muscle size and strength often take supraphysiological doses far larger than those induced by these methods. Furthermore, HGH injections clearly benefit individuals clinically deficient in the hormone1 So, the question still exists, “Do HGH injections benefit physical performance”?
The Effects of Human Growth Hormone Injections on Muscle Hypertrophy and Strength
Untrained Individuals
Yarasheski et al. studied the effects of HGH injections on changes in strength and body composition amongst 16 previously untrained men (mean age- 27 years) following a 12 week resistance training program2. Each participant was randomly assigned to either a placebo or the experimental group which received 40 μg rHGH/kg/day. Prior to initiating the 12 week training program, no significant differences were present between groups with respect to body composition (total body weight, fat mass, fat free mass). At study’s end, it was found that HGH injections did not significantly increase muscle strength gains (9 common exercises tested including shoulder, bench and leg presses) or size between the 2 groups. This happened despite significantly increasing circulating HGH (6x) and IGF-1 (4x) levels vs. placebo treatment (See below for explanation of IGF-1).
Both groups experienced similar gains in total body weight2. Although not quite statistically significant (p= 0.056) the HGH group tended to experience losses in fat mass. Those receiving HGH did experience significantly greater gains in fat free mass (which includes lean muscle tissue, connective tissue, body fluid, etc) vs. placebo. However, as pointed out by Yarasheski et al., no significant differences in muscle protein synthesis were found between groups. Furthermore, greater water retention was found in those given HGH. Thus, the research team concluded that chronic HGH injections do not augment muscle gains commonly observed following a 12 week resistance training program. Finally, it should be noted that the study originally included 18 individuals. However, 2 of the individuals receiving HGH had to drop out due to symptoms of carpel tunnel.
Insulin-like growth factor (IGF-1) is another hormone produced by the body that has anabolic effects on muscle tissue3. As seen in Figure 1, HGH stimulates the release of IGF-1, which is then believed to stimulate growth of muscle tissue. Few published studies have examined the effects of administering only IGF-1 on muscle growth. A study completed by Friedlander et al. indicated that receiving IGF-1 had no benefit on body composition or muscle strength in postmenopausal women4.
Figure 1. The hypothesized hormone pathway leading to increased muscle protein synthesis. Please note that this is an EXTREMELY over-simplified look at the process. Note the blue arrows coming in from the side. These represent other factors that are capable of increasing or decreasing the activity of this pathway.
Similar to HGH, current literature does not support the use of exogenous (of external origin) IGF-1 in already healthy individuals3. A more in-depth look at IGF-1 is beyond the scope of this article. For those interested in further discussion on it, I highly recommend reading _Regulation of muscle mass by growth hormone and IGF-I_. If you click on the title, this peer reviewed literature review can be obtained for free.
Trained Individuals
Deyssig et al. studied the effects of HGH injections in 18 male, lean, power trained athletes (mean age-23.4; 10% body fat)6. Over the course of a 6 week period, individuals received a placebo or 30 μg rHGH/kg/day. Despite significantly increasing circulating HGH and IGF-1 levels over this time period, HGH injections did not significantly alter gains in muscle strength, total body weight and fat mass. With respect to adverse effects, a case of carpel tunnel like symptoms developed in one participant using HGH. In closing, Deyssig et al. stated.
“We conclude that the anabolic, lipolytic effect of GH therapy in adults depends on the degree of fat mass and GH deficiency. In highly trained power athletes with low fat mass there were no effects of GH treatment on strength and body composition”6
Recently, Meinhardt et al. studied the effects of giving HGH, testosterone or the combination of the two on multiple measures of athletic performance and body composition16. Over the course of 8 weeks, 96 recreational athletes (>12 months of resistance training experience; mean age – 27.9 years) were assigned to the following groups:
Men (66 athletes)
- Testosterone (250 mg/wk)
- HGH (2 mg/day = ~30 μg/kg/d for a 70-kg person)
- Testosterone (250 mg/wk) + HGH (2 mg/day)
- Placebo
Women (33 athletes):
- HGH (2 mg/day)
- Placebo
Along with body composition, the researchers wanted to examine the effects of this supplementation protocol on VO2, vertical jump, anaerobic capacity (Wingate bike test), and isometric dead lift strength test (bar position not mentioned)16. At the end of the 8 weeks, all performance variables were the same between groups except the Wingate test. Compared to those taking the placebo, Men and women who received HGH experienced a 3.9% increase in anaerobic capacity. This increase in performance jumped to 8.3% in men who received both HGH and testosterone. With respect to body composition, HGH decreased fat mass and increased water retention. Body cell mass, an indicator of muscle tissue, significantly increased in those receiving the combined HGH + testosterone vs. placebo.
Six weeks after the final round of injections, Meinhardt et al. reassessed all performance variables to see if there would be any lasting effect. During this 2nd round of testing, all performance measurements were the same, regardless of if you received the placebo or HGH/testosterone treatment. As with the aforementioned studies, swelling and joint pain were common side effects in those receiving HGH.
Meta-Analysis
In a large meta-analysis, Liu et al reviewed all evidence to date (2008) that examined the effects of HGH injections on athletic performance or body composition changes in active, physically fit populations7. When combining the results of all 27 studies reviewed, it was found that lean body mass increased and there was a tendency for body fat to decrease. However, performance measurements such as muscular strength and aerobic capacity (VO2max) were not altered. Similar to Yarasheski et al2, Liu et al concluded that gains in lean body mass could be attributed to fluid retention rather than increases in contractile muscle proteins7. For reference, the 27 studies included 440 participants with the following characteristics: lean (BMI-24), young (mean age- 27 years), physically fit and received a mean dose of 36 μg HGH/kg/day. If you’re interested in reading the full paper (vs. my cliff-not version), it can be found by CLICKING HERE.
Does HGH Affect Protein Synthesis at All?
The question as to if HGH injections have anabolic effects in non-clinical populations may have finally been put to rest by Doessing et al8. In their study, 10 healthy, untrained men (mean age- 30 years) received HGH shots for 14 consecutive days (33 μg rHGH/kg/days 1-7; 50 μg rHGH/kg/days 8-14) after which they completed unilateral (single leg) leg extensions. 5 months later, the process was repeated except those who received HGH previously now received a placebo. Despite increasing circulating HGH levels by ~850% and insulin like growth factor (IGF-1) by ~320%, the rate of MPS was not significantly altered while receiving HGH injections vs. placebo treatment. Although MPS did not increase, HGH injections did increase collagen protein syntheses. For those unfamiliar with collagen, this protein serves as “guy wires” in the connective tissue of the musculoskeletal system. It’s found in tendons, bone, ligaments, muscles and cartilage. In contrast to myofibrillar proteins, collagen does not have any contractile properties. Rather it provides structural/connective support. In this study, the HGH injections increased collagen synthesis 1.3-fold in tendon tissue and 6-fold in muscle tissue. This led the authors of the study to conclude that:
“… rather than causing muscle fibre growth, GH/IGF-I appear to stimulate the supporting connective tissue that would help force transmission from the contracting muscle fibres to the bone.”8
Simply put, HGH does not appear to directly increase the size or strength of muscle tissue. It may indirectly increase muscular force capabilities (via strengthening support tissue), but to my knowledge, this has yet to be shown in exercise based research.
What About HGH Injections for Acting as “The Fountain of Youth”?
Does HGH stem off the physical decline seen with normal, healthy aging? That appears to be the popular question amongst the aging baby boomer population. Many anecdotal stories indicate that HGH can greatly enhance personal well-being and physical function as you age. Current scientific research to support these anecdotal stories is inconclusive and highly debated. In a recent review of the literature (completed in 2007), Liu et al. examined the effects of HGH injections in elderly individuals without any known health problems (ie- free of cancer, heart disease, diabetes, osteoporosis, etc)9. Their meta-analysis included results of 21 studies, consisting of 220 older, overweight individuals (mean age- 69 years; 33% women; BMI-28). Although great variation existed, the mean duration of each study was 27 weeks and average starting dose was 14 μg rHGH/kg/days. On one hand, results indicated that receiving HGH injections (vs. placebo treatment) > 26 significantly increased lean body mass (3.6 lbs; attributed to gains in water vs. actual muscle tissue) and decreased fat mass (5.1 lbs). On the other hand, those treated with HGH experienced significantly more “adverse events” such as carpel tunnel, edema, and arthralgias (joint pain). No significant differences were seen in bone density or blood lipid levels between groups.
Unfortunately, as noted be Liu et al., there was not enough information presented on physical function variables (ie- grip strength, 30 second sit-to-stand muscular endurance test, etc) and well-being measurements (mood profile, etc) to statistically analyze all of the purported benefits associated with HGH. However, in the small number of studies that did examine performance gains, HGH + exercise did not appear to increase muscular strength in trained10 or untrained1112 older individuals vs. exercise alone. Thus, looking only at the scientific data available to them, they concluded.
“Although GH has been widely publicized as an antiaging therapy and initial studies suggested that it might be clinically beneficial and safe in the healthy elderly, we find little evidence to support these claims. The scant clinical experience of GH in the healthy elderly suggests that although GH may minimally alter body composition, it does not improve other clinically relevant outcomes. Substantial evidence suggests that GH use in the healthy elderly is associated with high rates of adverse events. On the basis of available evidence, GH cannot be recommended for use among the healthy elderly.”9
For those interested in reading the full review completed by Liu et al, CLICK HERE
HGH + Testosterone
Although HGH alone does not appear beneficial, Sattler et al. demonstrated that HGH + testosterone was more beneficial than testosterone alone13. Their study involved 122 older, slightly overweight, men (mean age- 70.8 years; BMI- 27.4) with testosterone and IGF-1 levels “typical” for their age group. Over the course of 4 months, individuals were randomly assigned to receive various low dose testosterone and /or HGH combinations (Please see Table 1).
Table 1 Daily testosterone and HGH doses. Doses were chosen to reflect normal physiological level of these hormones vs. supra-physiological levels seen in other studies.
| Group | Testosterone Dose | HGH Dose |
| Group A | 5 mg/d (5g of a 1% testosterone transdermal Gel) | 0 μg rHGH/kg/day (placebo) |
| Group B | 5 mg/d | 3 μg rHGH/kg/day |
| Group C | 5 mg/d | 5 μg rHGH/kg/day |
| Group D | 10 mg/d (5g of a 1% testosterone transdermal Gel) | 0 μg rHGH/kg/day (placebo) |
| Group E | 10 mg/d | 3 μg rHGH/kg/day |
| Group F | 10 mg/d | 5 μg rHGH/kg/day |
After 4 months, it was found that increasingly greater hormone doses enhanced changes in body composition this seemed to be augmented with testosterone co-administration13. Individuals who received HGH + testosterone experienced significant increases in total body strength (based off composite scores obtained on leg press, leg flexion/extension, lat pulls & chest press) . With respect to cardiometabolic risk factors, insulin resistance, total and LDL cholesterol remained unchanged during the 4 month trial. Additionally, HDL cholesterol increased whereas triglyceride levels decreased. Outside of a small increase in fasting blood glucose, the only significant cardiometabolic risk factor negatively affected was blood pressure (systolic and diastolic blood pressure increased by 12 mmHG and 8mmHG).
Other Possible Benefits of HGH
From an orthopedic standpoint, HGH injections may be useful to those who have muscle-tendon, ligament, bone fractures or cartilage injuries. As seen in the study by Doessing et al., HGH does significantly increase collagen protein synthesis5. Studies completed by Raschke et al.14 and Van der Lely et al.15 provide some support to this possible use for HGH injections. However, more research is needed in this area before a definitive conclusion can be drawn.
Bottom Line
Strong evidence exists indicating that HGH administration does not increase muscle strength or size in healthy populations. Rather, it appears to increase collagen (the main protein in connective tissue such as bones, tendons, ligament, cartilage) and may be useful to those coming off injuries.
HGH injections have been shown to significantly decrease fat mass and increase lean body mass. However, improvements in lean body tissue are likely the result of increased water retention and non contractile tissues vs. actual gains in muscle mass.
Current, peer reviewed, scientific research does not support the “anti-aging” use of HGH in older populations. Although positive changes in body composition are observed, these benefits do not appear to increase strength or aerobic capacity. Resistance training has been shown to be just as effective as HGH + resistance training protocols with respect to increasing strength. Finally, HGH does not appear beneficial when taken alone. On the other hand, one recent study indicated HGH + testosterone does increase lean body mass and increase total body strength. Long term studies must still be carried out to further define potential quality of life/health benefits HGH + testosterone combinations may have in older adults.
References
1 Rennie MJ. Claims for the anabolic effects of growth hormone: a case of the emperor’s new clothes? Br J Sports Med. 2003 Apr;37(2):100-5.
2 Yarasheski KE, Campbell JA, Smith K, et al. Effect of growth hormone and resistance exercise on muscle growth in young men. Am J Physiol 1992;262:E261–7.
3 Velloso CP.Regulation of muscle mass by growth hormone and IGF-I. Br J Pharmacol. 2008 Jun;154(3):557-68.
4 Friedlander AL, Butterfield GE, Moynihan S, Grillo J, Pollack M, Holloway L, et al. One year of insulin-like growth factor I treatment does not affect bone density, body composition, or psychological measures in postmenopausal women. J Clin Endocrinol Metab. 2001;86:1496–1503.
5 Jacquemin V, Butler-Browne GS, Furling D, Mouly V. IL-13 mediates the recruitment of reserve cells for fusion during IGF-1-induced hypertrophy of human myotubes. J Cell Sci. 2007;120:670–681.
6 Deyssig R, Frisch H, Blum WF, et al. Effect of growth hormone treatment on hormonal parameters, body composition and strength in athletes. Acta Endocrinol (Copenh) 1993;128:313–18.
7 Liu H, Bravata DM, Olkin I, Friedlander A, Liu V, Roberts B, Bendavid E, Saynina O, Salpeter SR, Garber AM, Hoffman AR. Systematic review: the effects of growth hormone on athletic performance.Ann Intern Med. 2008 May 20;148(10):747-58. Epub 2008 Mar 17.
8 Doessing S, Heinemeier KM, Holm L, Mackey AL, Schjerling P, Rennie MJ, Smith K, Reitelseder S, Kappelgaard AM, Rasmussen MH, Flyvbjerg A & Kjaer M (2010). Growth hormone stimulates the collagen synthesis in human tendon and skeletal muscle without affecting myofibrillar protein synthesis. J Physiol 588, 341–351.
9 Liu H, Bravata DM, Olkin I, Nayak S, Roberts B, Garber AM, Hoffman AR. Systematic review: the safety and efficacy of growth hormone in the healthy elderly. Ann Intern Med. 2007 Jan 16;146(2):104-15.
10 Taaffe DR, Pruitt L, Reim J, Hintz RL, Butterfield G, Hoffman AR, Marcus R. Effect of recombinant human growth hormone on the muscle strength response to resistance exercise in elderly men. J Clin Endocrinol Metab. 1994 Nov;79(5):1361-6.
11 Yarasheski KE, Zachwieja JJ, Campbell JA, Bier DM. Effect of growth hormone and resistance exercise on muscle growth and strength in older men. Am J Physiol. 1995 Feb;268(2 Pt 1):E268-76.
12 Hennessey JV, Chromiak JA, DellaVentura S, Reinert SE, Puhl J, Kiel DP, et al. Growth hormone administration and exercise effects on muscle fiber type and diameter in moderately frail older people. J Am Geriatr Soc. 2001;49:852–858.
13 Sattler FR, Castaneda-Sceppa C, Binder EF, Schroeder ET, Wang Y, Bhasin S, Kawakubo M, Stewart Y, Yarasheski KE, Ulloor J, Colletti P, Roubenoff R, Azen SP. Testosterone and growth hormone improve body composition and muscle performance in older men. J Clin Endocrinol Metab. 2009 Jun;94(6):1991-2001. Epub 2009 Mar 17.
14 Raschke M, Rasmussen MH, Govender S, Segal D, Suntum M & Christiansen JS (2007). Effects of growth hormone in patients with tibial fracture: a randomised, double-blind, placebo-controlled clinical trial. Eur J Endocrinol 156, 341–351.
15 Van der Lely AJ, Lamberts SW, Jauch KW, Swierstra BA, Hertlein H, Danielle De Vries D, Birkett MA, Bates PC, Blum WF, Attanasio AF. Use of human GH in elderly patients with accidental hip fracture. Eur J Endocrinol. 2000 Nov;143(5):585-92.
16 Meinhardt U, Nelson AE, Hansen JL, Birzniece V, Clifford D, Leung KC, Graham K, Ho KK. The effects of growth hormone on body composition and physical performance in recreational athletes: a randomized trial. Ann Intern Med. 2010 May 4;152(9):568-77.