If you train in an oxygen-deprived gym you grow faster. Researchers at the Japan Institute of Sports Sciences believe this is because your body makes more growth hormone under these conditions.
The accepted theory is that training in an atmosphere that contains about 13-16 percent oxygen [hypoxia], instead of the normal 21 percent [normoxia], results in a higher concentration of lactic acid in the blood. This in turn leads to an increased release of testosterone and growth hormone, and therefore an enhanced anabolic response. At least, that's the theory.
Theories are a bit like commercials for abs machines. They look nice, but they don't necessarily work. That's why sports scientist Michihiro Kon got eight trained men to do the same workout twice: once in a normal environment, and once in a space where he had reduced the oxygen concentration to 13 percent using Hypoxico's Hyp-100.
(By the way: this machine costs about seven thousand euros, and a simple oxygen tent less than one thousand. If you have ten thousand euros or so to spare you could build your own hypoxia gym. Fitness centre owners have to fork out much more. Cheap it isn't, but renovating a building would cost more.)
Michihiro got his subjects to do five sets of bench presses and five sets of leg presses, using 50 percent of their maximal weight [1RM]. The men rested for 60 seconds between sets, and did 14 reps per set.
Before and after the workout the researchers measured the subjects' concentrations of lactic acid, cortisol, testosterone, noradrenalin and growth hormone in their blood. Of all the factors, only one reacted to the low-oxygen environment: growth hormone.
The researchers asked the subjects how tired they felt, but the oxygen-deprived environment had no effect on fatigue.
"Resistance exercise–induced increases in growth hormone secretion might be expected to play a role in promoting protein synthesis", the Japanese conclude. "It has been reported that the acute increase in GH secretion induced by resistance exercise correlates positively with the magnitude of muscular hypertrophy after training. Therefore, strength and conditioning coaches may consider low-intensity resistance exercise under systemic hypoxia as a potential training method for athletes who need to maintain muscle mass and strength during the long in-season."
This is a useful suggestion. Hypoxia training might therefore also be interesting for athletes in rehabilitation, elderly people or arthritis sufferers. Nevertheless, to us the mechanism behind enhanced muscle growth as a result of hypoxia training remains a mystery. Is the growth hormone peak really the only factor involved? Or do other variables also play a role? Maybe variables the researchers didn't look at?
J Strength Cond Res. 2012 Mar;26(3):611-7.