Breathing While a Mile High
I am currently in Denver, Colorado – a city famed for being “mile high” – and competing in the most important athletic ventures of my life so far. So, at 1609m above sea level how is the human body and athletic performance affected?
(Photo of the marker on the Colorado State Capitol building denoting one mile above sea level. Photo credit to Elliot Alder)
Short term changes
The process of acclimatisation begins as soon as you step off the plane; immediately your breathing rate increases. This is to try to combat the lower amount of oxygen in the air as there is about 17% less oxygen in Denver compared to Melbourne; because the pressure at altitude is less than the pressure at sea level. Basically, the air at altitude has less air above it to push all the molecules together compared to the air at sea level. While air at all altitudes is a constant 21% oxygen, the molecules of oxygen are more spread out the higher up you go. This means that each breath you take you are getting less oxygen, and so your body recognises its oxygen levels have dropped and increases the rate of breathing to try and combat that.
Generally, you don’t notice the increase in breathing until you try to do something more strenuous such as climbing some stairs. I definitely felt the lack of oxygen in the air while competing. After the first thirty seconds I would be very out of breath and fatigued. It was also harder to get my breath back on the bench even though we had canisters of oxygen to help.
Hyperventilation is the most important thing your body does to deal with the altitude, and it has a range of flow-on effects. For one, because you are taking more breaths you are breathing out more carbon dioxide. CO2 is acidic, and therefore lower levels of it mean your blood becomes alkaline. This is known as acute respiratory alkalosis and your body combats it by excreting more bicarbonate soda in its urine.
Other side effects
The thin air at altitude has been a recorded problem for humans for over 2000 years. But it has some other side effects that impact on your well-being at altitude such as dehydration and disrupted sleep.
Because you are taking more breaths and the air is drier, you lose a lot more water. My teammates and I had to be really careful to keep hydrated by drinking lots and lots of water. I’m not sure I have ever drunk as much water as consistently as I have while being in Denver.
Needing to breathe more also affects the quality and quantity of sleep you get while acclimatising to the altitude. Studies have shown up to 40 arousals a night and a 50% reduction in total sleep can occur at very high altitudes. I felt this pretty badly the first week or so, but other factors like jetlag, anxiety, and the room getting light in the morning probably contributed too.
Some effects of acclimatisation take your body a bit longer. When the kidneys sense the drop in oxygen in the blood, they create a hormone which tells the bone marrow to create more red blood cells. It will take over a week for the requested red blood cells to enter the bloodstream. There is also evidence suggesting that haemoglobin, the protein that binds oxygen to the red blood cell, changes how tightly it holds onto the oxygen. As well as creating more red blood cells, the body also increases the ratio of blood vessel to muscle mass, so your muscles can access your blood, and therefore oxygen, more easily.
I played in two tournaments while in Denver, one at the start and on at the end of my trip. I definitely felt the difference with the extra 12 days of acclimatisation time for my second tournament. I more or less felt normal and didn’t experience the breathlessness or fatigue I grappled with in the first tournament.
Many athletes include altitude training as part of their regime as the effect altitude has on the body – muscles becoming more efficient at using oxygen, creating more red blood cells – are similar to those you get from endurance training. However, one major drawback to training at altitude is that you physically can’t train as intensely as you can at sea level. Therefore, the training technique of ‘living high and training low’ has become more and more popular. By living at altitude, even for a couple of weeks, you get the beneficial physical changes of acclimatisation while you train at full capacity at a lower altitude. This method can significantly improve performance.
As red blood cells can live for up to 120 days, the changes from acclimatising to altitude can potentially last for that long too. So, I fully expect to have some kind of superhuman abilities to breathe when I get back to Melbourne.
Scientists are still learning about how the body reacts and adapts to high altitudes. Recently, they discovered two gene variants that help people who have lived at high altitudes for a long time like the Tibetans, cope with the thin air. Learning more about this will not only benefit athletes looking for that 1% advantage to win gold, but also will help with saving lives from blood loss from major trauma, tourists experiencing altitude sickness, and potentially even astronauts.