We’ve already discussed training at altitude (here). Hypoxia is the state when the body doesn’t get enough oxygen. Now, this can be from various physiological mechanisms breaking down, such as an V/Q mismatch or it can occur when training at altitude or in a hypobaric chamber or with a hypobaric mask on.
Given the idea that altitude training generally helps endurance athletes, the literature is replete with studies on hypoxic changes with endurance training. Let’s take a general review to see what’s going on.
The 2003 study on intermittent training under hypoxic conditions by Hendriksen and Meeuwsen had 8 male cyclists train for 2 hours/day for 10 days in a hypobaric chamber while 8 trained under normal conditions.
After 10 days of training, the hypoxia group demonstrated improved maximal power output by 5.2%, improved anaerobic mean power 4.1% and improved anaerobic power by 3.8%. VO2max was improved by 1.9%. The normalized condition group improved maximal power output by 2.1%, VO2max by 2.0% and mean and peak anaerobic power both by 0.2%. In contrast, the same authors published a 2001 study with the same protocol but demonstrated different results! VO2max had increased by 7.0%, mean maximal power by 7.4%, mean and peak power by 5.0%.
So while anaerobic and power based measurements are uniformly improved, the degree of improvement seems to vary quite widely.
Hoppeler and Voqt 2008 published a review of 27 articles on hypoxic training. Following the live low-train high adage they included studies where untrained individuals trained in a hypobaric chamber with relative oxygen ranging from 2300m to 5700m for 10 days to 8 weeks. Interestingly, molecular changes were consistent across the board but total effects (as seen above) varied widely. No conclusion on hypoxic training on mean power or VO2max could be agreed upon.
Similarly, Hoppeler and Voqt 2001 published a 6 week study in which untrained people trained for 2hrs/day at the equivalent of 3850m (in a hypobaric chamber). After 6 weeks, hypoxia inducible growth factor 1 and vascular endothelial growth factor and myoglobin mRNA all increased. This suggests that within a 6 week period of time, the body has finished its adjustments in attempting to get more oxygen.
Narici and Kayser 1995 had 5 male subjects train their biceps in a hypoxic chamber for 1 month. Cross sectional area of the muscle increased by 11.3% compared to 17.7% for those training under normal conditions. Max voluntary contraction increased by 9.5% compared to 13.6%. Muscle specific tension did not change. So clearly weight lifting for hypertrophy under hypoxic conditions is not ideal.
Pesta et al 2011 compared a group of untrained men training both endurance, by cycle ergometery, and strength under normalized and hypoxic conditions for 10 weeks. Fatty-acid oxidation increased at sea level in the endurance group by 260% and in the strength group by 240%. The hypoxia group demonstrated a 200% increase- muted compared to the others. However, they demonstrated that few mitochondrial changes occurred over the 10 weeks.
While all this physical training is helpful, at times sport requires mental agility as well. Knight et al 1990 had subjects live in a hypobaric chamber for 60 hours and had them perform arithmetic tests at hours 26 and 57. Oxygen levels were kept at 21%, 17% and 13% respectively. While the 17% group showed no significant drop in performance, the 13% group at hour 57 demonstrated a drop in cognitive abilities. Thus, in alpinism, we know that somewhere between hour 26 and hour 57, subjects cognitive abilities begin to drop off.
This is not an exhaustive review but we hope it helps shed light on the directions the current research is going.