Does human growth hormone improve performance?

Breaking down the findings on hGH

When our resident maven Jim Ferstle sent us the story about the how human growth hormone (hGH) can produce a 0.4 second improvement in 100 m sprinting, our ears pricked up and we were listening.  It got us searching for the article immediately, only to find that the current issue of Annals of Internal Medicine is not yet available electronically.  If you are at a university and want to read it now, maybe try heading down to your health sciences library and checking the current issues section for Issue #9 of that journal, where you will find the text by Udo Meinhardt.

But what we did find were several other articles on the topic, including a good review that examines several studies that have administered hGH in various subject populations.  So as a prelude to the most recent study, we thought we would provide some background on what the current evidence tells us about this hormone.

All athletes use it?

The first issue to address here is the widespread belief that those athletes who are doping are using hGH as part of their alleged cocktails of drugs.  We do know from books like Game of Shadows and by other admissions (Ben Johnson, Tim Montgomery, Lyle Alzado, and more) that some of the top athletes have indeed used the substance.  However until recently there has not been a test for the hormone, and so the reality is that we have absolutely no idea exactly how widespread its use really is.

But one thing we can be sure of is that, independent of what the science and physiology say, athletes are using it.  If we have learned anything from those athletes who have been caught and described their doping programs, it is that if they think it will provide some advantage, and if there is no test for it, it will quickly become a widely (ab)used substance.  Exhibit A:  Marion Jones taking EPO.  Too much is on the line for the athletes and the sporting administrators, and to think that top athletes in any sport do not dope is to be grossly naiive.

What the evidence tells us about hGH

We have not performed an exhaustive search by any means, but rather in response to the article that is about to be published in Annals of Internal Medicine we have rounded up an "executive summary" of what we know about hGH and sport.  Below is a table that we have reproduced from the review article "Growth hormone administration:  Is it safe and effective for athletic performance?" by the same group who have authored the Annals paper (click to enlarge):

The first thing you see is that the subject populations are varied, ranging from "highly trained" to "untrained."  In many ways this is no fault of the scientists---I can only imagine the difficulty in executing these kinds of studies, and so to add an additional high hurdle in the form of elite or even sub-elite athletes as the test subjects would be crazy.  No, these investigators have done the best they can for the most part, and so we cannot fault them outright for that, although we all would like to see the effects of hGH on much better athletes.

The real limitation:  Your model or mine

The problem as I see it is not one of the test subjects, but rather the paradigm within which these authors work and attempt to answer their questions.  On browsing through these studies it seems the primary approach is one of two paths.  First, some are interested in an acute dose on the effects of (fat) metabolism during exercise and rest, and second, others hypothesize that enhancing muscle mass and strength by itself translates into better performance.

And therein lies the limitation to this body of work---because from where we sit as sports scientists, the main effect of hGH (and most doping products) is that they allow the athlete to complete more training and harder training.  Thus they allow the individual to sustain a larger overload without breaking down and becoming injured, and therefore the adaptations they make are larger, which in turn leads to better performance.

Few drugs have an acute effect, or rather what we should say is that the drugs that do have an acute effect are easily detected---read, amphetamines---and these went by the wayside many years ago as testing for them became cheaper and more prominent and therefore the likelihood of getting caught increased.

The study we want to see is one in which trained runners or cyclists are administered hGH and then prescribed specific training that has been shown to improve their type of performance.  For example, a typical training intervention that has been proven to improve cycling performance is 4-5 min intervals at ~80% of peak power output.  Most cyclists respond well to this training, but we have always mentioned individual variation here---the "responders" vs. the "non-responders."  And so the question becomes whether or not the hGH administration alters this response to the training, either by allowing the "non-responders" to cope and make adaptations or by enhancing the adaptations of the "responders."

Coping with stress, the real advantage

In addition to elevating the amount of stress an athlete can sustain during periods of heavy training, the other thing hormones like hGH will affect is one's ability to recover between competitions, which of course are in and of themselves periods of high physiological stress.  One of the most interesting and telling articles I have read about doping is not scientific in nature, but was written by ultra-endurance cyclist and journalist Stuart Stevens for Outside Magazine back in November 2003 (you can also listen to an interview with him here).  The magazine fronted him the money to seek out and pay for doping products while he trained for Paris-Brest-Paris, a quadrennial 1200 km "fun ride" in France.  Stevens went on to take hGH, testosterone, EPO, and eventually anabolic steroids.  Here is a quote about a 200 mile qualifying race he completes:

"The last time I'd ridden 200 miles, I felt awful the next day, like I'd been hit by a truck. After the Solvang race I woke up and felt hardly a touch of soreness. I also felt like I could easily ride another 200, and I realized that I'd entered another world, the realm of instant recovery. I'll be frank: It was a reassuring kind of world, and I could see why people might want to stay there."

So when we say something "enhances performance," it is a qualified statement because that might mean it changes something directly related to performance, or it might also mean that something reduces recovery time thus allowing an athlete to complete more high-quality training and therefore make larger adaptations.  And not to mention the beneficial effects for athletes who complete in multi-day events who can wake up feeling, in Stevens' words, "hardly a touch of soreness," and ready to punish themselves for 4-5 h again the next day.

Sports Science meets Internal Medicine

The future of these studies will be when sports scientists team up with the internal medicine physicians who study the hormones and produce the training studies that will measure the true effect of drugs such as hGH on performance.  In the mean time, as is most often the case, how you interpret the available evidence depends entirely on your paradigm.  So if you think VO2max predicts performance, you administer hGH, show no effect, and conclude accordingly that hGH does not enhance exercise performance.  For now we will wait for the most recent study by Meinhardt to be published, and will follow up on this this post when we have a chance to digest it.

Jonathan


Some articles of interest:

Anything by HOLT and SONKSEN on Pubmed, they have written a virtual thesis on hGH.

Widdowson WM et al., The physiology of growth hormone and sport.  Growth hormone & IGF Research.  19:308-19, 2009.

Birzniece V et al., Growth hormone administration:  is it safe and effective for athletic performance?  Endocrinology and Metabolism Clinics of North America.  39:11-23, 2010.