The Science Behind Altitude Training: What drives the adaptations?

In this blog post we take a look at the science and unravel the fascinating chemical mechanisms in the body that drive some of the adaptations to altitude training. Specifically, we’ll be looking at what causes; increased red blood cell count, new blood vessel formation, increased mitochondrial density, and increased glycolytic metabolism.

Before we dive into the chemistry, it's important to grasp the fundamental challenge of altitude training; the air contains less oxygen. When athletes expose themselves to high altitude their bodies undergo a series of remarkable adaptations to maintain an adequate supply of oxygen.

Within minutes of high-altitude exposure, the peripheral chemoreceptors in the carotid arteries detect lower levels of oxygen in the blood. This sends a response to the brain to increase breathing rate and heart rate to keep up with the body’s requirement for oxygen. But the real benefits start to occur the longer the exposure.

Prolonged exposure results in a build-up of a protein called ‘Hypoxia-Inducible Factor 1a’ (HIF-1a). Normally, HIF-1a is found in relatively small amounts, but under hypoxic conditions it starts the build-up in the cells. As HIF-1a accumulates, it signals other genes in the body to express themselves, which underpin the adaptations.

Let’s take a look at some of the adaptations and the science behind them…

Increased red blood cell count

Erythropoietin (EPO) is a hormone produced primarily by the kidneys. Its main function is to stimulate the production of red blood cells in the bone marrow.

At higher altitudes, your body senses the decreased oxygen levels and in response, your kidneys release EPO into the bloodstream. EPO travels to the bone marrow, where it stimulates the production of erythroblasts (immature red blood cells). These erythroblasts evolve into reticulocytes (young red blood cells) and then take 1-2 days to mature into erythrocytes (red blood cells).

Red blood cells contain a protein called haemoglobin, and it is this protein that oxygen and carbon dioxide bind to and hitch a ride to and from your muscles. The more red blood cells we have, the more oxygen we can carry to our working muscles, and the more carbon dioxide we can take away!

New blood vessel formation

HIF-1a targets a gene called Vascular Endothelial Growth Factor (VEGF). At first, VEGF works by making your blood vessels widen (vasodilate) which increases blood flow, but after prolonged exposure it also causes your body to create new blood vessels – known as capillarisation. These new blood vessels permeate into areas of the muscle to allow oxygen-rich blood to penetrate deeper and supply the working muscle.

New studies are now showing that exposure to high altitudes result in increased capillarisation of the brain too. Scientists are now studying how altitude exposure can be used to combat certain brain diseases and reduce the risk of a stroke!

Increased mitochondrial density

Mitochondria, often called the powerhouse of the cell, are vital for energy production. Exercising in a normal oxygen environment naturally increases skeletal muscle mitochondria, however, when exercise is done at altitude there is a compounding effect.

Exercise done in a low oxygen environment causes HIF-1a to spark the creation of new mitochondria, a process known as mitochondrial biogenesis. The more mitochondria we have, the
more energy we can produce, and the more efficiently the mitochondria can access the low levels of oxygen in the blood.

Increased glycolytic metabolism

In hypoxic environments, most cells shift their source of energy from oxidative (aerobic) to glycolytic (anaerobic) pathways to keep up with energy requirements (demand for ATP). HIF-1a does this by increasing the expression of glycolytic enzymes. These enzymes are responsible for glycolysis (carbohydrate metabolism) which produce and supply ATP quickly. ATP is the primary fuel source in cells, so the quicker ATP can be sourced, the better. For athletes, being able to create ATP quickly results in more forceful ‘bursts of energy’.


Altitude training embodies the intriguing interplay of science, adaptation, and evolution. It’s easy to see why humans who populate high altitude areas, or utilise altitude training, excel.


About the Author

Jake Ward Sales Manager, Altitude Training Systems

Jake Ward is the Sales Manager at Altitude Training Systems and has a background in strength and
conditioning, as well as applied sports science, having worked with elite sporting organisations and
sport technology companies.

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