Sunday, May 30, 2010

Growth hormone may rise 300 percent with exercise: Acute increases also occur in cortisol, adrenaline, and noradrenaline

The figure below (click to enlarge) is from the outstanding book Physiology of sport and exercise, by Jack H. Wilmore, David L. Costill, and W. Larry Kenney. If you are serious about endurance or resistance exercise, or want to have a deeper understanding of exercise physiology beyond what one can get in popular exercise books, this book should be in your personal and/or institutional library. It is one of the most comprehensive textbooks on exercise physiology around. The full reference to the book is at the end of this post.

The hormonal and free fatty acid responses shown on the two graphs are to relatively intense exercise combining aerobic and anaerobic components. Something like competitive cross-country running in an area with hills would lead to that type of response. As you can see, cortisol spikes at the beginning, combining forces with adrenaline and noradrenaline (a.k.a. epinephrine and norepinephrine) to quickly increase circulating free fatty acid levels. Then free fatty acid levels are maintained elevated by adrenaline, noradrenaline, and growth hormone. As you can see from the graphs, free fatty acid levels are initially pulled up by cortisol, and then are very strongly correlated with adrenaline and noradrenaline.  Those free fatty acids feed muscle, and also lead to the production of ketones, which provide extra fuel for muscle tissue.

Growth hormone stays flat for about 40 minutes, after which it goes up steeply. At around the 90-minute mark, it reaches a level that is quite high; 300 percent higher than it was prior to the exercise session. Natural elevation of circulating growth hormone through intense exercise, intermittent fasting, and restful sleep, leads to a number of health benefits. It helps burn abdominal fat, often hours after the exercise session, and helps builds muscle (in conjunction with other hormones, such as testosterone). It appears to increase insulin sensitivity in the long run. Maybe natural elevation of circulating growth hormone is one of the “secrets” of people like Bob Delmonteque, who is probably the fittest octogenarian in the world today.

Aerobic activities normally do not elevate growth hormone levels, even though they are healthy, unless they lead to a significant degree of glycogen depletion. Glycogen is stored in the liver and muscle, with muscle storing about 5 times more than the liver (about 500 g in adults). Once those reserves go down significantly during exercise, it seems that growth hormone is recruited to ramp up fat catabolism and facilitate other metabolic processes. Walking for an hour, even if briskly, is good for fat burning, but generates only a small growth hormone elevation. Including a few all-out sprints into that walk can help significantly increase growth hormone secretion.

Having said that, it is not really clear whether growth hormone elevation is a response to glycogen depletion, or whether both happen together in response to another stimulus or related metabolic process. There are other factors that come into play as well. For example, circulating growth hormone increase is moderated by sex hormone (e.g., testosterone, estrogen) secretion, thus larger growth hormone increases in response to exercise are observed in older men than in older women. (Testosterone declines more slowly with age in men than estrogen does in women.) Also, growth hormone increase seems to be correlated with an increase in circulating ketones.

Heavy resistance exercise seems to lead to a higher growth hormone elevation per unit of time than endurance exercise. That is, an intense resistance training session lasting only 30 minutes can lead to an acute circulating growth hormone response, similar to that shown on the figure. The key seems to be reaching the point during the exercise where muscle glycogen stores are significantly depleted. Many people who weight-train achieve this regularly by combining a reasonable number of sets (e.g., 6-12), with repetitions in the muscle hypertrophy range (again, 6-12); and progressive overload, whereby resistance is increased incrementally every session.

Progressive overload is needed because glycogen reserves are themselves increased in response to training, so one has to increase resistance every session to keep up with those increases. This goes on only up to a point, a point of saturation, usually reached by elite athletes. Glycogen is the primary fuel for anaerobic exercise; fat is used as fuel in the recovery period between sets, and after the exercise is over. Glycogen is expended proportionally to the number of calories used in the anaerobic effort. Calories are expended proportionally to the total amount of weight moved around, and are also a function of the movements performed (moving a certain weight 1 feet spends less energy than moving it 3 feet). By the way, not much glycogen is depleted in a 30-minute session. The total caloric expenditure will probably be around 250 calories above the basal metabolic rate, which will require about 63 g of glycogen.

Many sensations are associated with reaching the glycogen depletion level required for an acute growth hormone response during heavy anaerobic exercise. Often light to severe nausea is experienced. Many people report a “funny” feeling, which is unmistakable to them, but very difficult to describe. In some people the “funny” feeling is followed, after even more exertion, by a progressively strong sensation of “pins and needles”, which, unlike that associated with a heart attack, comes slowly and also goes away slowly with rest. Some people feel lightheaded as well.

It seems that the optimal point is reached immediately before the above sensations become bothersome; perhaps at the onset of the “funny” feeling. My personal impression is that the level at which one experiences the “pins and needles” sensation should be avoided, because that is a point where your body is about to “force” you to stop exercising. (Note: I am not a bodybuilder; see “Interesting links” for more extensive resources on the subject.) Besides, go to that point or beyond and significant muscle catabolism may occur, because the body prioritizes glycogen reserves over muscle protein. It will break that protein down to produce glucose via gluconeogenesis to feed muscle glycogenesis.

That the body prioritizes muscle glycogen reserves over muscle protein is surprising to many, but makes evolutionary sense. In our evolutionary past, there were no selection pressures on humans to win bodybuilding tournaments. For our hominid ancestors, it was more important to have the glycogen tank at least half-full than to have some extra muscle protein. Without glycogen, the violent muscle contractions needed for a “fight or flight” response to an animal attack simply cannot happen. And large predators (e.g., a bear) would not feel intimated by big human muscles alone; it would be the human’s response using those muscles that would result in survival or death.

Overall, selection pressures probably favored functional strength combined with endurance, leading to body types similar to those of the hunter-gatherers shown on this post.

Even though the growth hormone response to exercise can be steep, the highest natural growth hormone spike seems to be the one that occurs at night, during deep sleep.

Exercising hard pays off, but only if one sleeps well.


Wilmore, J.H., Costill, D.L., & Kenney, W.L. (2007). Physiology of sport and exercise. Champaign, IL: Human Kinetics.


F. Belt said...
This comment has been removed by a blog administrator.
Ned Kock said...

Are you referring to the hunter-gatherers on the linked post?

Ned Kock said...

I've just noticed that the first comment was spam, so I deleted it.

LeonRover said...

Hi Ned

While not a practitioner in the science, I've had a copy of McArdle, Katch, Katch - Exercise Physiology - since 2000. It is now looking a little tired!

Does your recommended text cover

i) Phinney's work on ketones as nutrients for exercise; or

ii) Gibala etc on HIIT.

I am an "older guy" but not a Delmonteque.

Just want to keep those muscles while eating low amounts of complex carb.

Ned Kock said...

Hi Leon.

I did a "search inside this book" on the Amazon entry, and it does not look like they cite Phinney or Gibala.

Ned Kock said...

They do cite Fleck & Kraemer a lot, which is a good sign.

LeonRover said...

Thank you for that Ned.

Kindke said...

I think people like Bob are myostatin gene mutated. Im sure we all know people that are naturally muscular without doing anything.

I have a good feeling however that the primary purpose of growth hormone and therefore its strongest stimulus is to crank up FFA metabolism.

I dont think glycogen depletion in muscle is important, I think whats important is Glycogen depletion in the liver for growth hormone, becuase then we REALLY need to get FFA metabolism going for ketones to fuel the brain. Glycogen depletion in the liver is a serious issue from the bodies point of view becuase its the liver's job to regulate blood sugar levels and if it drops even a bit you get severe nausea and all sorts of problems.

Further evidence is the fact that sugars get a fast track to the liver via the portal vein after consumption, from that point on the liver decides whether to build more glycogen or turn it into fat.

Lastly, we have the fact that growth hormone and insulin are strong antagonsists, high insulin = high carbs = high carb metabolism = no use for FFA = low growth hormone

Ned Kock said...

Hi Kindke.

Very good and thoughtful points.

Lyle McDonald, who blogs at, told me that he doesn't think that GH influences FFA much. Indeed, when you look at the graph on the right in this post, the correlation between GH and FFA is not very high; much lower than the correlation between adrenaline and FFA.

One thing to bear in mind regarding liver glycogen depletion is that it is not increased that much by resistance exercise. In fact, resistance exercise produces lactate, which is then used by the liver for gluconeogenesis, sparing liver glycogen.

Yet, GH secretion increases dramatically with resistance exercise, and is highly correlated with muscle glycogen depletion. This depletion is very localized. Only the muscle groups that are worked can become depleted.

W: Eight said...
This comment has been removed by a blog administrator.
Ned Kock said...

To commenter "W: Eight":

Your comment was deleted because it looked like spam to me. If not, it added absolutely nothing to the discussion.

Sorry if I deleted it by mistake, but if it was not spam it was an incoherent comment at best.

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js290 said...


just read through your post again after reading this abstract:

RT (resistance training) increases muscle mass, with a very wide range of effectiveness in humans. We therefore determined the expression level of 21 abundant miRNAs to determine whether variation in these miRNAs was able to explain the variation in RT-induced gains in muscle mass.

Put the hunter-gatherers through Mike Mentzer training, and they'd probably still look a lot like the way they do in the picture perhaps more sculpted. Let Mike Mentzer live with the hunter-gatherers for a while, and he'd probably end up with roughly a less sculpted version of the physique he's known for.

If the glycogen depleting stimulus is there, the body is going to adapt towards its genetic potential. The degree of the stimulus would likely determine how much of one's potential one's able to reach, but it doesn't seem like it would matter whether that stimulus occurred in the Australian Outback or at Gold's Gym.

Ned Kock said...

Hi js290.

Yes, I also think that the stimuli are the key, with the body taking care of much of the rest.

Some people just want to become what they are not, and they keep wondering if they are doing something wrong.

A 150-lb frame will never hold 250 lbs without some very unnatural things happening. And vice-versa.

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