Human Growth Hormone-Part I: Does it enhance physical performance?
Quick Hit Summary
Human Growth Hormone (HGH) has been shown to improve body composition in individuals clinically deficient in the hormone. Thus, many athletes have designed their workouts around maximizing the release of this hormone. However, current research does not support the theory that HGH stimulating workouts actually increase muscle protein synthesis. HGH workouts may increase fat loss but more research needs to be completed in this area. Multiple studies have also looked at if oral amino acids (L-arginine, L-ornithine, GABA, etc) can enhance natural HGH production. Currently, very little evidence supports their use in young or old individuals.
Human Growth Hormone
Human growth hormone (HGH). Is there a hormone over the past 10 years that has gained more attention in main stream media? During this time period, it has gone from a word generally reserved for the scientific community to a common household term. Much of this can be attributed to well known athletes such as Barry Bonds, Roger Clemens, Marion Jones and others who have been linked to this performance enhancing drug. Even non athlete celebrities, such as Sylvester Stallone, swear by it. Due to its name, many individuals commonly believe that human growth hormone (HGH) will improve muscle size and strength. Furthermore, HGH has been shown to improve body composition (ie- lean body mass, % body fat) in those clinically deficient in the hormone1. For these reasons, HGH has piqued the interest of both competitive athletes and exercise enthusiast.
The Effects of Exercise Induced Human Growth Hormone on Muscle Hypertrophy and Strength
Single Training Session
HGH is naturally produced by the body in response to intense workouts that are characterized by high rep sets and short rest intervals (ie- the same type of workouts that create a “burning” sensation in your muscles due to lactic acid buildup)2. These workouts have been shown to significantly increase circulating HGH concentrations for up to 30 minutes post-exercise in both men and women. Recently, West et al. analyzed the relationship between exercise induced HGH elevations and muscle growth. In the first of their 2 studies, 8 healthy, untrained males (mean age- 20 years) completed 2 separate resistance training sessions; one was a high hormone (HH) session that significantly increased HGH release (single arm preacher curls followed by intense leg training) and the other was a low hormone (LH) session which failed to increase circulating HGH levels (preacher curls only; completed on the arm opposite of the one used in the HH session)3. Following each session, researchers measured the rate of myofibrillar protein synthesis (MPS) in the bicep of the respectively trained arm. {For reference, myofibrillar proteins are the proteins which are responsible for generating force in the muscle during muscular contraction. Via resistance training, one increases the synthesis of myofibrillar proteins, leading to gains in both muscle strength and size.}. Results indicated that despite increasing circulating HGH levels (~800%), the hormone stimulating workout failed to significantly improve MPS vs. the arm only training session.
Figure 1 % Increase in muscle protein synthesis after high and low hormone training sessions. As you can see, the low hormone session increased muscle protein synthesis by 78% whereas the high hormone session increased it by 61%. These differences were not statistically different from each other.3
Please don’t misinterpret the graph… If one quickly looks at the graph, he/she may assume that the LH session increases muscle protein synthesis vs. HH session. However, I must emphasize that these differences were not statistically significant.
Chronic Training
The aforementioned study only looked at how a single session influenced the rate of muscle protein synthesis. One may naturally wonder what would happen if this protocol was repeated over an extended time period. Maybe, the cumulative effects of elevating HGH levels would influence MPS. Thankfully for us, this very question was answered in a 2nd study completed by West et al4. The design and exercise routine of this study was similar to their previously mentioned study except participants (12 untrained males; mean age 21.8 years) completed 15 weeks of training using the following routine:
- Weeks 1-6: exercised 3x/week alternating between HH (single arm preacher curls and LH routines every other training day.
- Weeks 7-15: exercised 4x/week alternating routines every other training day.
Pre- and post- workout protein shakes have been shown to influence muscle growth5 and are commonly used by athletes. Thus, each participant received 18 grams of whey protein just prior and again 90 minutes following each session to mimic real life training4. At the completion of the 15 week training period, West et al. examined increases in muscle size and strength of each arm. Both biceps, regardless of if it was trained under the HH or LH conditions, experienced similar increases in both muscle size (Figure 2) and strength gains (Figure 3).
Figure 2. % Increase in Type I and Type II muscle fiber size following 15 weeks of a high or low hormone training protocol. The method of training (high hormone, low hormone) had no effect on changes on either type 1 or 2 muscle fiber size.4
For reference, Type 1 are “slow” twitch muscle fibers and used primarily for endurance based training and smaller in size. Type II are “fast” twitch muscle fibers and used primarily for max strength/power based contractions. They are much larger in size vs. Type I. Also, there were no significant differences in muscle fiber size between groups at the start of the trial.
Figure 3. % Increase in 1 rep max and 10 rep max following 15 weeks of a high or low hormone training protocol. The method of training (high hormone, low hormone) had no effect on changes on either type 1RM or 2RM.4
There were no significant differences in 1 or 10 rep max between groups at the start of the trial.
The Effects of Exercise Induced Human Growth Hormone on Fat Loss
Although exercise induced HGH workouts will not enhance muscle growth, they may be useful for decreasing body fat. One of the physiological functions of HGH is to increase lipoloysis (breakdown of fat for energy purposes)6. There has been some evidence that intense exercise, which stimulates HGH, may decrease total abdominal fat. This was demonstrated in a study completed by Irving et al. in which 27 middle aged women (mean age – 51 years) were assigned to a control, low intensity or high intensity aerobic training program for a total of 16 weeks7. Duration of each exercise session was adjusted such that individuals in the high and low intensity training groups burned equal kcal/session. At the conclusion of the study, those participating in the high intensity training group saw significantly greater losses in visceral and total abdominal fat vs. those in the low intensity group. Study authors hypothesized that results were due to greater release of lipolytic hormones (such as HGH). On the other hand, when men of a similar background were added to the study results, (exercise conditions held exactly the same) no differences were present between groups8.
Study Limitations
There are two caveats worth mentioning regarding the aforementioned studies looking at high intensity aerobic workouts, HGH and fat loss. First, dietary records were not kept. Thus, differences in dietary intake may account for the changes seen. Second, Irving et al. did not present data reflecting HGH levels in the study involving the 27 middle aged women7. As such, there is a lack of definitive evidence indicating that exercise induced HGH release leads to greater losses in fat mass vs. exercise of equal kcal expenditure that fails to raise circulatory HGH release. Also, I’m unaware of any study which has looked at this potential benefit in a young, healthy adult population. Thus, with respect to the scientific literature, the jury is still out on the effectiveness of exercise inducing HGH workouts on accelerating fat loss vs. non HGH stimulating aerobic workouts of similar kcal expenditure.
Growth Hormone Secretagogues
If one looks on the internet, he/she can find many products that are alleged to enhance the body’s natural production of HGH. These products, commonly referred to as HGH secretagogues, often consist of the amino acids Gamma-aminobutyric acid (GABA), arginine, ornithine, and lysine.
Gamma-aminobutyric acid
Research has indicated that Gamma-aminobutyric acid (GABA) stimulates HGH secretion in subjects at rest9. For this reason, its been advertised to strength athletes as a natural way to “stimulate secretion of growth hormone, decrease body fat levels and increase lean muscle tissue.”10 Using this as a backdrop, Powers et al examined if 3 grams (g) of GABA would enhance both resting and exercise induced levels of HGH11. On four separate occasions (2 resting sessions, 2 exercise sessions), 11 resistance trained men (mean age- 23.6 years) received either HGH or a placebo treatment. Blood levels of ifGH, which is believed to be the biological active form of HGH, was measured for 90 minutes following ingestion. At rest, GABA supplementation significantly increased mean ifGH levels vs. placebo (>300%). Also, GABA vs. placebo tended to increase ifGH levels during exercise. At 30 minutes post-ingestion ifGH was significantly greater (175%) in the exercise + GABA vs. exercise + placebo. It also tended to be higher over the entire 90 minute observation period.
To my knowledge, the effect of long term GABA supplementation on body composition in active or sedentary individuals has not been studied.
Arginine
Arginine is one of the more popular amino acid HGH secretagogues. Evidence exists indicating that oral doses of 5 and 9 grams of arginine could significantly increase HGH levels in resting individuals12. In a classic study completed by Collier et al., the effects of arginine on resting and exercise (including post-exercise) HGH levels were examined13. Their study involved 8 males (man age- 20.4 years) who participated in the following four sessions:
- Rest + Placebo
- Rest + l-Arginine (7 g)
- Exercise + Placebo
- Exercise + l-Arginine (7 g)
Circulating HGH levels were measured after each exercise or resting session. With respect to stimulating HGH release, results were as follows:
(In descending order of greatest HGH stimulation over entire measuring time frame)
#1: Exercise + Placebo
#2a. Exercise + Arginine
#2b. Rest + Arginine
#3. Rest + Placebo
Supplementing with arginine did increase HGH vs. baseline values. However, the greatest HGH levels were found after exercise-placebo session, followed by exercise-arginine session. Let me put this another way. Arginine + exercise actually DECREASED HGH (by 50 %) vs. exercise alone when measured over the entire recording period. Additionally, as seen in Figure 4, Arginine also blunted the peak HGH release normally seen during exercise.
Figure 4 Percent increase in HGH levels vs. baseline after arginine consumption and exercise.4 All of these increases were significantly greater than baseline measurements.
It should be noted that some studies have failed to find any benefit of arginine on HGH levels. This was seen in a study completed by Marcell et al. who gave ~ 4 grams of arginine to both young (mean age-22) and older (mean age- 68.5) participants14. In contrast to Collier et al.13, Marcell et al.14 failed to find any stimulatory effect for arginine on HGH levels in subjects at rest. Arginine also came up short with respect to enhancing exercising HGH levels. These results were observed in both the older and younger age groups. It should be mentioned that no placebo pill was given in this study. Rather, they just compared HGH levels during and following an exercise only session vs. arginine(4g) + exercise session.
Amino Acid Combinations
L-arginine & L-lysine
Suminski et al. gave 16 men (mean age- 22.4) 1.5 g lysine + 1.5 g arginine under both resting and exercising conditions15. At rest, HGH was significantly increased (270%) 60 minutes post ingestion, but no significant differences were found at 30 and 90 minutes. During exercise conditions, no significant differences were seen between the amino acid and placebo treatments.
L-arginine, L-ornithine & L-lysine
Fogelholm et al. completed an interesting study in which 11 trained weightlifters (19-35 years of age), took L-arginine, L-ornithine & L-lysine prior to a training session as well as just prior to going to bed16. 1 g of each amino acid was taken at both time periods for a total daily dose of 6 grams. After four days of this routine, the researches found that “*supplementation did not affect the physiological variation of serum hGH concentration*.”16
L-arginine & Aspartate
Abel et al. randomly assigned 30 endurance trained athletes to either a placebo, high supplement (5.7 g arginine and 8.7 g aspartate), or low supplement (2.8 g arginine and 2.2 g aspartate) groups for a duration of 4 weeks17. At study’s conclusion, Abel et al. found no differences in HGH levels between any of the groups.
What does this all mean?
When an effect is seen with amino acids on circulating HGH levels, it appears to occur only under resting, fasted conditions. The important question one has to ask themselves is, “Do these small transient increases in HGH, induced by amino acids, have any significant effect on body composition or performance?“ Exercise induced HGH secretions were shown to have no effect on myofibrillar protein synthesis (MPS), muscle strength or size in the aforementioned study by West et al.34. This lack of effect on MPS occurred despite an 8 fold increase in peak HGH levels4, which is greater than the peak increase seen with most of the amino acid supplements18.
Before I go any further evaluating all of this research on amino acids and HGH, there is one BIG problem that needs to be mentioned. As pointed out by Chromiak and Antonio, HGH secretions are usually stimulated to a greater degree following an overnight fast18. Thus, if you’re going to take these HGH secretagogues, one should probably do it on an empty stomach. In the above studies that showed a positive effect of GABA11 and arginine13 on HGH, the amino acids were given following an overnight fast. In addition, individuals in the GABA and arginine trials waited > 90 minutes before having any food after the amino acid ingestion. When putting this into practice, I feel that it would be very foolish for any exerciser/athlete to follow this type of a fast. After an overnight fast, catabolic forces are at full throttle in your body, destroying your hard earned skeletal muscle20. This metabolic state must be reversed and one of the best ways to accomplish this is by eating anabolic foods… one should not prolong it simply to get a little more benefit from an amino acid HGH secretagogue!
Don’t get me wrong. I’m not saying that taking supplements containing amino acids are bad. In fact some studies have shown a beneficial effect of taking some of the above mentioned amino acids. Elam et al. found that taking 1 gram of both arginine and ornithine in conjunction with a 5 week resistance training program led to significantly greater gains in lean body mass and total strength vs. those taking a placebo19. However, I feel these gains are completely independent of HGH. As seen in the studies by West et al., HGH does not appear to increase MPS in young, healthy individuals.
What About taking These Amino Acids as You’re Getting Older to Assist HGH
If I wanted to play the devil’s advocate, I could point out that all but 114 of the studies showing little to no effect were done on a younger population who normally have high HGH levels. However, research seems to indicate that with increasing age, one is less responsive to a given dose of various HGH secretagogues21. A dose of 1.5 g lysine + 1.5 g arginine has been shown to stimulate HGH in young adults (mean age 22.4)15. Yet, even when this dose is quadrupled (6 g of each amino acid), HGH levels fail to significantly rise in older adult men (mean age- 69)22.
Bottom Line
There’s strong evidence that exercise induced HGH secretions have no anabolic effect on the contractile fibers (myofibrillar proteins) of muscle tissue in healthy (ie- not clinically deficient in HGH) populations. With respect to the current scientific literature on fat loss, the jury is still out on if exercise inducing HGH workouts (aerobic) are more effective than non HGH inducing workouts (aerobic) when kcal expenditure is held constant. If you’re going to do high rep, short rest intervals do it to train a certain metabolic system, not spike hormone levels.
Various studies provide evidence that amino acids can act as HGH secretagogues in resting individuals111213. However, this finding is not universal amongst all studies14. Additionally, when taken prior to a training session, it appears that taking HGH secretagogues will have no effect or actually reduce the exercise induced levels of HGH.
Amino acids are great supplements to use in conjunction to an exercise program due to their ability to directly stimulate protein synthesis23. I use various amino acid supplements myself. However, the current scientific research just doesn’t support their ergogenic effect via a HGH pathway/mechanism. Rather I think they work via a non-HGH pathway/mechanism to enhance muscle size/performance. For this reason, I feel they are wrongfully promoted as “HGH Secretagogues” since their beneficial effect on body composition/performance is likely through a non-HGH pathway.
And with that, Human Growth Hormone-Part I comes to an end, but stay tuned for Part II of this story when we bring out the big boy… HGH injections!!!
References
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