Simulated Altitude Training

The Physiology of Altitude

When athletes train at high altitude, the lower atmospheric pressure means there is less oxygen available per breath. The body senses this sustained hypoxia (low oxygen) and compensates by releasing a hormone called Erythropoietin (EPO) from the kidneys.

EPO stimulates the bone marrow to produce more red blood cells. More red blood cells mean a higher oxygen-carrying capacity, resulting in increased VO2 max and endurance when the athlete returns to sea level.

Can Breathwork Simulate Altitude?

Yes, through a technique called Intermittent Hypoxic Training (IHT), or more specifically in this context, deliberate hypoventilation during exercise.

By intentionally holding your breath while exercising (e.g., swimming, cycling, running), you rapidly deplete the oxygen in your blood while simultaneously driving up carbon dioxide (hypercapnia). When blood oxygen saturation (SpO2) drops below 90% repeatedly during a training session, the kidneys respond identically as they would at altitude: by secreting EPO.

The Spleen Contraction

In addition to the long-term EPO response, there is an immediate, acute response to breath-holding: the mammalian dive reflex triggers spleen contraction.

The spleen acts as a reservoir for red blood cells. Studies on freedivers have shown that after three maximum breath holds, the spleen contracts, squeezing highly oxygenated red blood cells into circulation. This temporarily increases hematocrit (the volume percentage of red blood cells) by up to 10%, providing a sudden boost in oxygen-carrying capacity.

How to Practice (Hypoxic Walking)

The safest way to begin simulated altitude training is through hypoxic walking.

1. Walk at a normal pace while strictly breathing through your nose.
2. After a minute, exhale normally through your nose, pinch your nose with your fingers, and continue walking.
3. Count the number of paces you can take while holding your breath.
4. When the urge to breathe becomes moderate to strong, let go of your nose and inhale through your nose. (If you have to gasp through your mouth, you held it too long).
5. Recover with normal nasal breathing for 1-2 minutes.
6. Repeat 5 to 8 times per session.

Over weeks of practice, your pace count will increase as your CO2 tolerance improves and your body adapts to lower oxygen levels.

Buffering Lactic Acid

Another major benefit of this training is improved buffering capacity. Because holding your breath during exercise causes a rapid buildup of CO2 (which makes the blood acidic), the body is forced to improve its ability to buffer acidity (often erroneously referred to as lactic acid buildup). This delays the onset of muscle fatigue during high-intensity efforts.