If ever there was a hormone that could enhance fat loss and build muscle, growth hormone is it, ranking right up there with testosterone as one of the two most important. Scientists aren’t yet sure of the exact role GH plays in muscle building and fat burning, but they do know one thing…it’s important! There’s still debate on exactly how much bodybuilders need for increasing muscle mass and losing fat, but without GH, your chances of getting the physique you want are slim to none. FLEX is here with new proven data that GH is a powerful and important hormone for both fat loss and muscle building.

GH, also known as somatotropin, is a peptide hormone produced by the anterior lobe of the pituitary gland. GH secretion declines with advancing age, which may be the reason for the loss of lean muscle mass and increased adiposity that occurs with aging. Furthermore, research shows that in aging men, the extent of pulsatile GH release declines by 50% every seven years after 18–25 years of age.

At rest, GH secretion is characterized by episodic bursts over a 24-hour period, and is influenced by many factors, such as age, gender, nutrition, sleep habits, body composition, regional distribution of body fat, degree of fitness, and exposure to stress, as well as sex hormone (testosterone and estrogen), insulin, and IGF-1 levels. GH has been found to have the following direct and indirect effects on muscle and other organs: Direct effects are the result of GH binding its receptor to target cells. For example, adipocytes, or fat cells, have GH receptors on their surface to break down triglycerides and suppress their ability to take up and accumulate circulating lipids.

Indirect effects are mediated primarily by the insulin-like growth factor-1 (IGF-1), a hormone secreted by the liver and other tissues in response to GH. A majority of the growth-promoting effects of GH are actually due to IGF-1 acting on its target cells.


The most appealing aspect of GH is its direct effect on fat metabolism. In animals and humans, GH has been reported to have direct fat-burning effects on adipose tissue. In short, GH turns on your body’s fat-burning machinery and turns off its fat-storage mechanisms. GH puts the brakes on the body’s primary fat-storage enzyme, lipoprotein lipase (LPL). One study reported that when GH was given to obese subjects, there was a 65% reduction in adipose tissue LPL activity. So GH is inhibiting the enzymes involved in the fat-storage machinery.

Also important is the ability of GH to enhance fat mobilization. GH has powerful fat-mobilization properties; but when GH is enhanced, this is where the real results come in. For example, an earlier study gave subjects either GH infusions or a placebo during 20 minutes of high-intensity cycling. The subjects receiving GH injections had higher GH levels; but the rise in GH in response to exercise was directly related to subjects’ fat utilization two to three hours after exercise. Researchers concluded that GH peaks during exercise can increase post-exercise fat utilization; in essence, it’s like stepping on the fatloss accelerator after exercise.


Chronic exposure to GH has been shown to increase fat mobilization via an increase in free fatty acids; GH also inhibits the conversion of glucose into lipids, and decreases adipose tissue. Also, increasing GH during exercise is vital to increasing fat metabolism. Increasing both GH and catecholamines (adrenaline) by increasing exercise intensity may have a dual effect on fat loss by different mechanisms. It’s much like adding gasoline to the fi re: When high-intensity exercise is performed, there is a marked increase in GH production.

A previous study reported that there was a dose-dependent relationship between exercise-intensity levels and GH levels post-exercise. In this study, five treadmill-running intensities were studied at various percentages of the subjects’ lactate threshold. In exercise physiology, lactate threshold is the intensity at which lactate (lactic acid) starts to accumulate in the blood stream. When the researchers tabulated all the data, the results of the study showed that the degree of fat utilization post-exercise was directly related to increases in GH and epinephrine (adrenaline) secretion during exercise. GH was found to be the strongest marker for postexercise fat utilization. Additionally, the degree of fat utilization during the recovery period was related to the exercise-intensity level.


So now you may be asking, how powerful are the acute spikes in GH that occur with exercise? To demonstrate, researchers gave healthy subjects a dose of GH that was equivalent to a high-intensity exercise session at rest. They found that a single dose of GH in the normal physiological range of intense exercise resulted in a 60–250% increase in adipose lipolysis two to three hours after administration.

Now, a new study in the journal Growth Hormone and IGF-1 Research reports similar findings. Subjects in the study were assigned to either GH infusions or a placebo during a high intensity cycling bout for 20 minutes. The subjects receiving GH injections had higher GH levels, but the subjects’ rise in GH in response to exercise was directly related to their post-exercise fat utilization two to three hours after exercise. The researchers concluded there’s a delay in fat-burning capacity for one to two hours between the GH peak during intense exercise, and the rise in fat mobilization after exercise. GH increases during exercise do not sustain lipolysis during exercise, but do result in enhanced mobilization after exercise.

As mentioned previously, in addition to exercise, sleep is also a powerful stimulator of GH secretion. In fact, today’s reported epidemic of sleeplessness is no doubt a contributor to the current obesity epidemic. To prove how important sleep is in enhancing GH, researchers stuck needles directly into subjects’ stomachs and measured the direct mobilization of fats from adipose tissue. The study concluded that neglecting to get enough sleep—and, consequently, getting no nighttime rise in GH—led to a reduction in fat mobilization in abdominal adipose tissue the next morning.


In the last issue of FLEX, we revealed some very exciting news about the potential applications for GH as an important factor for enhancing muscle mass. To recap, the newest study in the European Journal of Applied Physiology showed that increases in both GH and cortisol in response to long-term exercise were associated with increases in type II fibers and lean muscle mass. Researchers examined 56 healthy (but untrained) young men who took part in a 12-week resistance-training program, measuring testosterone, growth hormone, IGF-1, and cortisol concentrations at the beginning and end of the study. The biggest winners for increased muscle growth appeared to be GH and cortisol. This demonstrated that long-term episodic spikes in GH and cortisol are important for gains in muscle mass. The study also showed that muscle hypertrophy is a complex cascade of actions by a symphony of hormones.

Long-term gains may be due in part to GH’s direct effects on skeletal muscle protein synthesis. A recent study isolated satellite cells (precursors to muscle cells) and examined whether GH or IGF-1 had a direct effect on their activation. To the researchers’ surprise, GH directly affected skeletal muscle growth, in part through stimulation of protein synthesis in the muscle. They also found that this stimulation is not mediated through increased IGF-1 expression in the muscle.

And now, even more exciting news: In the past, GH has only been available by injection, but according to a report presented at the Obesity Society’s prestigious 30th annual Scientific Meeting, an alternative in pill form is in the offing. Researchers examined the effect of Growth Factor 9, a specific amino acid supplement blend, on an empty stomach after an overnight fast. Amazingly, 120 minutes after ingestion of a single oral supplement of Growth Factor 9, GH levels increased eightfold over baseline levels (the equivalent of a 682% raise). Even more encouraging, the increases in GH were similar to levels obtained after a 0.06 IU subcutaneous injection of GH in GH-deficient subjects.

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