Why is Breathing at Altitude so hard?

What happens when we travel up in elevation? Why do athletes go to higher elevation to train?
To start we need to talk atmospheric pressure. As we go up in elevation, the pressure decreases. Decreasing pressure means there is less stuff moving around in the air. The air around us is roughly 21% oxygen at sea level and on top of mountains. Yet because the atmospheric pressure is lower on top of mountains, it means there are fewer molecules in the air. So while 21% of the molecules are still oxygen, there are fewer of them. Consequently when we are higher up and we inhale, we inhale thinner air or fewer molecules of oxygen with each breath we take.

Since we inhale less oxygen with each breath, as our exertion level increases, we have to work harder to get the same quantity of oxygen that it would normally get at a lower elevation.

Why is it so hard?
Chemoreceptors in the arteries of our neck sense the reduced oxygen levels, causing our breathing rate and our breathing depth to increase. However this increased breathing volume causes our carbon dioxide levels to decrease which makes it harder for our bodies to meet their oxygen needs (we need carbon dioxide for the red blood cells to let go of the oxygen).

These same chemoreceptors also tell our nervous system that something is different and we need to get ready (activates the sympathetic nervous system). With this increased arousal our heart rate increases, our digestion is impaired, and our urination increases as our blood volume decreases. The plasma part of the blood decreases so that are concentration of red blood cells is proportionally higher.

Our respiration rate, heart rate, and blood pressure typically all go up. For some individuals a higher altitudes, our respiration or breathing rate and heart rate may double while at rest. Everyone is a little different, some folks will be more affected than others based on your fitness level, lung capacity, tolerance to lower levels of oxygen, tolerance to range of carbon dioxide conditions, etc.

Why does it get easier over time?
Our bodies change to compensate for the lower quantities of oxygen. The aclimitization process can take days or weeks.

We first increase red blood cell production to carry more oxygen around; our kidneys produce more Erythropoietin or EPO to make this happen. After about 3 days, the body will have more red blood cells. The amount of red blood cells will continue to increase for some time and will eventually plateau at higher level of red blood cells appropriate for the specific altitude. For example to fully acclimatize to 10,000 feet or 3,000 meters typically takes up to 35 days.

After about 4 days, the kidneys help balance the pH of blood by producing more bicarbonate to compensate for the higher ventilation rate (lower carbon dioxide), which makes it easier for the body to access the available oxygen.

Our bodies will also start to produce more capillaries making it easier for the blood to get to various cell tissues via increased pathways.
Our lungs will start to expand more fully with a typical breath, increasing our lung capacity.

However, even with these bodily adaptations, we may not achieve the same level of physical and mental fitness that was typical at lower elevations.  Strenuous exercise and memorization tasks often still remain more difficult for 6 or more months. Other physiological factors may impact how easily and quickly someone adapts. For example, if your iron levels are low, the body will have a harder time increasing the quantity of red blood cells.

Why do athletes go to elevation to train?
The physiological changes that happen in body don’t instantly disappear when we return to lower elevations. It can take 1-2 weeks for our bodies to readapt to being a a lower elevation. The increased oxygen in our blood and our body’s access to these higher levels of oxygen mean that it is easier to oxygenate our working muscles under exertion. When we first decrease in altitude, it’ll feel easier to work out.

Rather than training at altitude some athletes have taken Erythropoietin or EPO to cause their bodies to produce more red blood cells. EPO is one of the drugs that Lance Armstrong took during his cycling career.

Can breathing exercises help?
Yes – many breathing exercises can help to prepare to go to altitude and to help your body adjust at altitude.

Any breathing exercises that increase breathing efficiency and lower resting respiratory rate will make it easier to breathe at higher altitude. In general, nose breathing, breath hold exercises and slower paced breathing exercises could be beneficial to prepare.

Since chemoreceptors in the blood initiate the changes when we go to altitude, we can perform various exercises to increase the normal range of these chemoreceptors. Performing really long breath holds (this takes effort but can be achieved with practice) where the oxygen levels begin to decrease, let our bodies know that it’s normal and safe to have lower levels of oxygen in the blood. Consequently our ventilation rate will stay lower as we increase in elevation, keeping our levels of carbon dioxide higher and making it easier for our body to access the oxygen available.

Once at altitude, exercises to help calm the nervous system are helpful, for example, breathing in and out through the nose, into the lower ribs expanding in all directions, and as slowly and smoothly as is comfortable.