The theory of the altitude tent is relatively simple. Sleeping in a hypoxic ( which means less oxygen than the “normal” 21% oxygen content of “air”) tent attempts to simulate some of the beneficial physiological responses that are well-established for athletes living in real-world high altitude environments. Although there are several mitochondrial and metabolic changes that contribute to the benefits of high altitude living, the primary adaptation that people are after is:
-Increased Erythropoiesis (what the heck is that?…it really just means making more red blood cells)
When there are lower oxygen levels circulating in your blood (as is the case at altitude because the air is “thinner” and there is relatively less of every atmospheric gas, including oxygen, as compared to sea level) your kidney actually detects this low oxygen level and releases a hormone called erythropoietin, or EPO. EPO then circulates in your body and tells your bone marrow to start producing more red blood cells. More red blood cells result in increased oxygen carrying capacity of blood, hence increasing the oxygen in your blood to maintain the balance that keeps the kidney happy. This increase of oxygen in the blood also boosts performance in endurance-related sports because more oxygen to muscle means the muscle can do more work, experience less fatigue and have less lactic acid produced for a given amount of exercise. More oxygen carrying also implies a higher VO2max for those who like buzz words. This EPO hormone is the same hormone that has made many professional cyclists infamous- the only difference is the injectable one is made in a lab, but it is the same hormone. Interestingly, the primary legitimate medical indication for EPO use is kidney failure for the reasons described above. The question remains whether or not a simulated hypoxic tent environment actually replicates this same biological response seen at altitude?
Diagram of Erythropoiesis (making more red blood cells)
Hypoxic Vs. Hypobaric:
A very important distinction to make when assessing altitude tents is the difference between hypoxic and hypobaric. In the real world, high altitude is a hypobaric state. Hypobaric means that all atmospheric gases are “thinner” at higher altitudes and therefore less abundant. While less oxygen is available at high altitude, 21% of the “air” is still oxygen. The way an altitude tent works is different. An altitude tent works under a hypoxic environment instead of a hypobaric environment. The air has the same “thickness” as the altitude at which the tent is set up. The hypoxic tent environment replaces part of the percentage of the “air” that is oxygen with nitrogen. Hypoxic (and normobaric) means you are breathing less than 21% oxygen but the air is still “thick” like at sea level. Unlike real altitude, there are lots of gas molecules around in a tent, just a little more nitrogen and a little less oxygen than the normal breakdown of air. The hypoxic vs. hypobaric distinction becomes very important when we look at the potential limitations of altitude tents and reasons why some physiological responses may be different.
Of note, “normal” air is about 78% nitrogen anyways so nitrogen is very abundant and it won’t hurt you to breathe a little more of it for anyone who may think breathing nitrogen sounds scary.
Responders Vs. Non-Responders
The term “responder” is a commonly used term in the altitude tent literature. It simply means that some people experience benefits from the tent in similar ways to altitude, while others do not. No one quite knows why it works for some people and not others. It is probably multifactorial and very complex. There has been a particular interest in studying the association of a particular enzyme genotype, call the angiotensin converting enzyme, in association to whether or not someone is a “responder.” This angiotensin converting enzyme is just a fancy name for an enzyme in our bodies that contributes to blood pressure control and it is postulated that it also plays a role in how we adapt to altitude, although the mechanism for this theory is not understood. People inherit different versions of the gene that is in charge of this enzyme and it might make a difference what version of the gene you have. In short, some people may respond while others do not and we don’t really know why, but different gene makeups probably play a significant role.
So do the tents work….???
Ah ha! So I have done a review of the current published scientific literature on this topic and I will be posting my impressions very very shortly….stay tuned….
Next topic up…Does compression wear really do anything?? Or are you just being duped into buying some really expensive old man tube socks??