If I understand correctly, hypoxic training (done by endurance athletes) works by forcing the body to adapt to low oxygen concentrations, i.e., improve oxygen metabolism. For this, athletes go to higher altitudes or use special machines (“hypoxicators”) that change the air they are breathing.
Could a similar effect be achieved simply by being in a (small enough) closed room for a long enough time, such that the oxygen concentration is as low as desired?
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You would need an air tight sealed room thas probably way more expensive than any other option. And then you still need to measure the CO2 levels and oxygen levels in that room to not kill the athlete.
No, because carbon dioxide buildup would be a problem. Someone trying this would feel the ill effects of too much CO2 long before they had any significant impact from lowered oxygen levels.
You would have to constantly monitor the proportion of CO2 to O2, which is non-trivial to do in a safe way, then vent or add in gas to compensate (and make sure it’s getting to the person). Meanwhile the room needs to be big enough that you can do things in it, while still being relatively airtight. Finally, your body reacts differently to high CO2 air than it does low O2 density air (like being at high altitudes). So with all that expense and engineering, it’s easier to just rent a place in the mountains.
One of the quietest ways to accidentally *die* is to have a low oxygen environment in a small room.
This is because low oxygen isn’t immediately recognizable by our brain (we have good CO2 detectors to make us breathe, but bad O2 detectors), and once it does happen we lose enough of our coordination that *leaving* the low oxygen area doesn’t happen (or we just pass out).
Now, could it be safely done by controlling the air inside a room with a machine, making sure it’s just low O2 and not too low? Perhaps. But at that point might as well use the hypoxicator.
Product development ( the airflow restriction mask) has convinced people to perform hypoxic training the opposite way it is actually intended to be performed. True altitude training means living at high altitude and training at lower altitude. Training with lower levels of o2 restricts performance gains, offsetting any type of “training your body to better use o2”. Living at high altitude increases red blood cell counts and efficiency, which allows you to train harder when at lower altitudes, which allows longer an more intense training sessions.
It’s been a while since I’ve done exercise physiology, but let’s see if I can remember it. If I’m wrong, someone will correct me.
Air is made up about 78% nitrogen, 21% oxygen, and about 1% carbon dioxide, with some other stuff thrown in there. It doesn’t matter where you are in the world, be it on Everest or in a jungle, it’s about that mixture. What changes is the pressure.
When you are at sea level you have all the air above you pushing down and creating pressure. Kinda like in water, the deeper you go, the more pressure due to the water above you. The air you breathe works on a gradient, from high to low. So the oxygen is forced through the lungs membrane by the atmospheric pressure. As you go higher, there is less air above you and less pressure to push the oxygen into your body. The mixture remains the same.
When you are at sea level, your red blood cells (RBC) are about 99% oxygen. But as you go higher, with less oxygen being forced into your body, the RBC might only be about 80% oxygen. To accomodate this, you will start breathing faster and heart pump faster. What this does is make your body create more RBC to help transport the little oxygen around.
Now your idea of a hypoxic chamber would have a similar effect of high altitude, but as you are changing the levels of oxygen, you’d be putting the athlete at risk. For instance, a study found that taxi drivers have very high hematocrit (RBC), because they are breathing in fumes in a low oxygen environment because they are around cars in a city all day suffering from low levels of carbon monoxide exposure. It would be safer to place them in a hypobaric chamber. But as someone else mentioned, it’s the living at altitude that makes the difference, not the training.
There is another, and arguably more effective method, and that would to train in heat, which essentially dehydrates the body, reducing blood volume (blood is mostly water). The body adapts by creating more blood.
Confined spaces with even just a few percent lower O2 than ambient air are a huge safety concern for construction and facility operations. Like people have died just turning wrenches in small rooms with poor ventilation after a surprisingly short time. Athletic hypoxic training is way safer and easier to do than what would be needed to train in a sealed room. As others have said, the co2 will kill you before you start running out of oxygen:
“The American Conference of Governmental Industrial Hygienists (ACGIH) recommends an 8- hour TWA Threshold Limit Value (TLV) of 5,000 ppm [.5%] and a Ceiling exposure limit (not to be exceeded) of 30,000 ppm [3%] for a 10-minute period. A value of 40,000 [4%] is considered immediately dangerous to life and health (IDLH value).”
Well, from my experience in altitude physiological trainers. First, you don’t even need a room, you can do it with an oral-nasal mask. This is the basis of ROPD (Reduces Oxygen Partial-Pressure Devices). The US Military has been using these for the recurrent altitude training for some years. See [HERE](https://armyaviationmagazine.com/robd-hypoxia-training/). The army now says they’re even going to do initial altitude training with them. This is because they discovered that frequent altitude exposures was producing changes in the white matter of the brain. In the pilots, particularly HA like the U2, and also in the instructors who were going to 27k (100% O2) and 42k ft (Pressure-breathing) on a regular basis. Breathing on a mask and dumping the exhaust you don’t need to monitor CO2. But even in a closed room, monitoring CO2 takes a monitor you can buy off the shelf.
One thing here is that actual exericse triggers adaptations via more than one mechanism. A state of hypoxia due to breathing air that doesn’t have enough oxygen would not trigger the same sort of adpatations in the human body as endurance exericses do. The main task in the latter is much more specific: a high need to deliver oxygen to certain working muscles, while also simultaneously asking your muscles to stick to a smooth running/cycling/skiing/rowing technique despite getting tired, flushing away waste products, etc.
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