Training in Hypoxia Accelerates Isometric Strength (+24%) + Size (+1kg) Gains as Well as Fat Loss (-4%) in 5-Week Study

In hypoxia you still have to work out intensely & consistently to get shredded.

This is not the first time you read about the almost marvelous effects a low oxygen environment can have on the adaptive response to exercise, but after reading it, you will hopefully agree that it was one of the most interesting SuppVersity articles about hypoxia.

The article discusses the results of a recent study from the Journal of Strength and Conditioning Research by Yan et al. In said study, the authors tested the effects of different levels of systemic hypoxia on the hormonal responses, strength, and body composition to 5-week resistance training.
To this ends, Yan et al. recruited twenty-five "physically active" male subjects with previous resistance training experience and randomly assigned them to one out of 3 experimental groups that performed 10 sessions (2 sessions per week) of barbell back squat (10 repetitions, 5 sets, 70% 1 repetition maximum [RM]) under

• normoxia, i.e. in a regular gym (NR, FiO2 = 21%),  or
• severe (HH) or moderate (HL) hypoxia (HL, FiO2 = 16%; HH, FiO2 = 12.6%). 

Serum growth hormone (GH), testosterone (T), and cortisol (C) concentrations were measured before (Pre) and at 0 (T-0), 15 (T-15), 30 (T-30) minutes after exercise in the first and last training sessions. The subjects' one repetition maximum (1-RM), their isometric knee extension, isometric leg press (LP), and body composition were evaluated before and after the protocol.

Figure 1: Hormonal response to resistance training under normal or reduced oxygen conditions; inerestingly, the effects on the testosterone / cortisol ratio increased, while those on GH decreased over time (Yun. 2015).

As you can see in Figure 1, the hormonal response the scientists observed during the first and last sessions in hypoxia foreshadowed the significant differences in the adapative response Yun et al. observed. To be more specific, the benefits materialized during the post-tests in form of significant improvements in isometric LP strength and an exclusively significant increase in lean body mass in the hypoxia groups (meaning the increase in the normoxia group was not significant).
In view of the fact that we are dealing with a moderate-intensity resistance training program, the former is as unsurprising as the significant isometric strength increases and lean mass changes in hypoxia are surprising.

Figure 2: Rel. Changes in strength and body composition over the course of only 5 weeks of training (Yan. 2015); please note that the absolute reduction in BF% was only 2% in the hypoxia and 1% in the normoxia group/s.

Whether these effects (see Figure 2) were in anyway mechanistically related to the significantly greater GH responses in the hypoxic training groups, however, remains questionable (see light blue box). The increased GH response could after all be a mere correlate of a different underlying mechanism that triggers both - the accelerated adaptive processes, subsequently increased gains and + fat lass and the temporarily elevated growth hormone levels. This hypothesis is further supported by the lack of differences between the training effects in the HL and HH group. If those were triggered by the observed acute changes in the so-called "anabolic hormones", the more beneficial testosterone to cortisol ratio (see Figure 1) would have had to trigger a greater adaptive response in the HH group. The fact that it didn't is quite revealing. After all, the testosterone to cortisol ratio is still regarded as the most important marker of anabolism by the average bodybuilding forum visitor.

The mask on the right does not simulate training in hypoxia and cannot be expected to help effortlessly shed 11% of body fat as it was observed in a 2013 study in trained athletes.

Ah... and now that we are already talking about the things people write in fitness forums, I should maybe mention that the "fitness masks" with which you look pretty much like Hannibal Lecter can not replace a hyperbaric chamber or a mask with separate low O2 air supply. Why? The masks make it harder to breath. That has a certain training effect, because it trains the diaphragm, but this effect is (a) much more pronounced in (relatively) untrained individuals than in athletes and (b) and achieved by totally different mechanisms (Stuessi. 2001), of which we cannot assume that they have the same extended (beyond the training session) metabolic effects that make "true" hypoxia so effective.
References:

• Ho, Jen-Yu, et al. "Effects of acute exposure to mild simulated hypoxia on hormonal responses to low-intensity resistance exercise in untrained men." Research in Sports Medicine 22.3 (2014): 240-252.
• Kon, Michihiro, et al. "Effects of systemic hypoxia on human muscular adaptations to resistance exercise training." Physiological reports 2.6 (2014): e12033.
• Raastad, Truls, Trine Bjøro, and Jostein Hallen. "Hormonal responses to high-and moderate-intensity strength exercise." European journal of applied physiology 82.1-2 (2000): 121-128.
• Stuessi, Christoph, et al. "Respiratory muscle endurance training in humans increases cycling endurance without affecting blood gas concentrations." European journal of applied physiology 84.6 (2001): 582-586.
• Yan, Bing, et al. "Effects of Five-Week Resistance Training in Hypoxia on Hormones and Muscle Strength." The Journal of Strength & Conditioning Research 30.1 (2016): 184-193.