Med Sci Sports Exerc. 2009 Dec 14. [Epub ahead of print]
Effects of Acute Hypoxia on Metabolic and Hormonal Responses to Resistance Exercise.
Kon M, Ikeda T, Homma T, Akimoto T, Suzuki Y, Kawahara T.
1Department of Sports Sciences, Japan Institute of Sports Sciences, 3-15-1 Nishigaoka, Kita, Tokyo, 115-0056, Japan; 2Laboratory of Regenerative Medical Engineering, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan.
INTRODUCTION:: Several recent studies have shown that resistance exercise combined with vascular occlusion effectively causes increases in muscular size and strength. Researchers speculated that the vascular occlusion-induced local hypoxia may contribute to the adaptations via promoting anabolic hormone secretions stimulated by local accumulation of metabolic subproducts. Here we examined whether acute systemic hypoxia affects metabolic and hormonal responses to resistance exercise. METHODS:: Twelve male subjects participated in two experimental trials: 1) resistance exercise while breathing normoxic air [normoxic resistance exercise (NR)], 2) resistance exercise while breathing 13 % oxygen [hypoxic resistance exercise (HR)]. The resistance exercises (bench-press and leg-press) consisted of 10 repetitions for five sets at 70 % of maximum strength with 1-min rest between sets. Blood lactate, serum growth hormone (GH), epinephrine (E), norepinephrine (NE), insulin-like growth factor 1 (IGF-1), testosterone, and cortisol concentrations were measured before normoxia and hypoxia exposures, 15-min after the exposures, and at 0, 15, 30, 60 min after the exercises. RESULTS:: Lactate significantly increased after exercises in both trials (p < style="color: rgb(153, 51, 0);">These findings suggest that resistance exercise in hypoxic condition caused greater accumulation of metabolites, and strong anabolic hormone response.
What is it with Japanese research and oxygen deprivation? They bring us the most amazing results of occlusion training (b2d discussion here). Now, how about whole body oxygen occlusion?
Some may argue that this seems to be similar to training at altitude, where the benefits are known. Indeed, the authors use a system that's used to generate Everest-like conditions, funnily enough called an "everest generator" and for 5K you can have one, too (shown left).
Thing is, this technique is most often used for endurance athletes (and we've also seen in cycling for instance blood doping associated cases of EPO enriched/adapted blood), and apparently the usual oxygen depletion levels are 20.9% o2 - with associated increased risks of overtraining. Here, in this resistance training study, the researchers use 13ish% o2.
Another unique aspect of this hypoxia study is it's the first time (to my knowledge anyway) researchers have formally looked at effects on resistance training - anaerobic effort as opposed to aerobic effort.
The Rationale: it IS occlusion training. The authors do indeed say yup well, LOW INTENSITY resistance training and partial occlusion has great effect, so how about "systemic hypoxia" - It's the next logical step, isn't it?
Set Up. 10 reps of bench and squat at 70% of tested 1RM in either normal room air or 13% O2. I'm only able to guess that 13% is some standard definition of "acute hypoxia" conditions that are still safe.
The authors alas don't formally justify either why they were going for this percentage or why this definitely NOT low resistance level (like occlusion training uses) was used.
All sorts of Measures. The purpose of the trials were so the researchers will have
examined the effects of resistance exercise on metabolic and hormonal responses under acute systemic hypoxia. We hypothesized that the resistance exercise in hypoxic condition would cause greater accumulation of metabolic subproducts, and greater responses of anabolic hormones.To this end, a lot of measures were taken of muscle oxidation, hormones, fuel produced (like lactate). As the abstract says, blood lactate levels were significantly higher in the hypoxia trial than in the normal air trial. This isn't much of a surprise, given that lactate tends to kick in as it gets harder for the body to oxidize fuel in the mitochondria. A goal of Vo2max training (like viking warrior conditioning, reviewed here) is to increase the lactate threshold - the level of effort and time before which bi products of lactate production (H+ ions) can no longer be buffered out of the blood.
And what all the lads love to hear: serum GH - significantly higher in the hypoxia case (potentially triggered, the researchers suppose by increased catecholamine release) Likewise IGF and of course yes the big T, testosterone. But so does cortisol.
And for those trying to burn fat? Not surprisingly to folks who see the world through the nervous system threat/no threat lense, those wonderful fight or flight catecholamines are of course elevated, too. These are the things that help fat mobilisation (discussed here in this b2d piece on HIIT). So gosh, let's see - challenge trying to breath - i'd say that's going to be perceived as a threat to one's system?
So What's Different (than occlusion training)?
The authors suggest that while occlusion training has shown greater muscle growth, they haven't really known why. They put it down to the increased levels of GH noted in occlusion training at LOW REPS. Here they're saying
In the present study, we revealed that systemic hypoxia was actually associated with greater GH response to resistance exercise for the first time. The hypoxia may play a key role in the low intensity resistance training with vascularInteresting that systemic hypoxia is being used to understand the mechanisms of a more local phenomena like Kaatsu cuffing.
occlusion-induced muscular hypertrophy
What they say their specific results also suggest is that IGF-1 may be indedpendent of GH levels. In other words, something else is going on to get a boost in IGF-1 than the presence of GH.
Likewise, they suggest that increases in serum testosterone may have more to do with intensity and muscle mass than "metabolic stress" - like hypoxia.
As for cortisol, another fight or flight hormone, that's also a known biproduct of resistance training. The researchers say they just don't know what the mechanism is such that these levels are particularly higher in this trial. Well heck, again, threat-related hormone; gonna asphixiate. Dunno. seems predictable when seen from that vantage?
Not Normal. The threat hormones did not return to normal levels within an hour after the trials either. Is that good? Not clear, but if overtraining is related to stressing they system, threatening it more than it can handle perhaps, then it's reasonable to see why this kind of training may need to be far more closely monitored for overtraining effects.
Openning New Doors. The biggest outcome it seems right now is the possible relationship of hypoxia to GH - at least in the authors' view:
... it is necessary to investigate whether hypoxic exposure plays an important role for the expressions of genes involving muscular hypertrophy in the future...Our data suggest that hypoxia is a potent factor for the enhancements of anabolic hormone (GH) response to resistanceWhy when fleeing the Tiger does GH turn on? Intriguingly, we already induce a kind of hypoxic environment in anaerobic work like resistance training - hence the term anaerobic - so it's interesting to see therefore that the hypoxic effect seems to be perhaps on the recovery - where we usually pause between sets to catch our breath and re-oxygenate. Here, in this o2 deprived envrionment, that can't happen. Hence lactate it seems to me goes up. And GH switches in.
Why, when the nervous system might be percieved to be under threat, would the nervous system/brain see this as a good time to, er, grow? (For a review of the systems that get shut down under stress, see this overview of Zebras and Baboons and Stress.)
Again, what these researchers don't seem to clue into is that growth hormone is apparently known to be triggered by stress (and here's a pdf from 76 about how kind of cool this is, where only 1/3 of the sample group was shown to have this particular stress/GH release response). It's role this work shows, is not just to grow the body, but the brain. Is that what's going on? I'm about to die; i suddenly need a bigger brain?
Ramdoc, over at the dragondoor forum (thank you), made the intriguing connexion that GH is related to insulin. Here's 2005 paper outlining the human GH/insulin homeostasis, and that bigger hits of GH lead to a hyperinsulinism - elevated levels of insulin in the bloodstream. That's gonna trigger a temporary blood glucose surge. So if increased GH relates to a rush of glucose to the bloodstream, that certainly would have a survival effect. More fast energy, that means more ATP, more muscle can be recruited, more speed, steve. Cool.
We're about to Die; Let's get Huge?
Well who'd have thought even to test the effects of cutting off circulation to see what would happen to our bodies?
I suppose it's an interesting idea - take a process like anaerobic metabolism and string it out to see if by seeing what happens in a less natural environment, we get some better view into a natural environment. And heck, some folks might turn that practice into a way to rehab and train folks.
The responses seen in this environment - a big fat rush of fight or flight related responses - seem pretty predictable. That there's a positive payoff FROM that stress after the event is interesting: survive and get faster, stronger. Recovery means anabolism: more muscle, continued performance improvement. And who knows? Maybe a bigger smarter brain?
But in terms of pushing this principle that's being expressed in the large in this oxygen deprived space? The biggie that those stress levels don't go back to normal in normal time is a reminder that hypoxia work may just be super stressful to our CNS even if we mayn't perceive that directly ourselve - and this study doesn't tell us if it collected any of the athletes' responses to the protocol.
In the meantime, for those who are curious, how would one try this at home without an Hypoxia Generator? The mind reels at the possibilities.