Blog Launch: Cracking the Code of Altitude Training

As athletes continue to embrace the mountains, they unlock new levels of endurance and resilience, paving the way for greater achievements in their running journeys.

For decades, altitude training has been hailed as a performance booster for endurance athletes. But while many embrace the concept, few truly understand the complex physiological changes that occur at high elevations. The reality? Success at altitude isn’t just about training harder, it’s about understanding and tracking the right biomarkers to support optimal adaptation.

The Altitude Effect: What Happens to Your Blood?

The moment you arrive at altitude, your body senses the lower oxygen levels and begins adapting to maintain performance. One of the most important changes is an increase in hemoglobin concentration, which allows your blood to carry more oxygen. This happens in two stages. First, plasma volume drops (you lose some fluid), concentrating the blood. Next, red blood cell production ramps up and is driven by a hormone called erythropoietin (EPO), which is triggered by low oxygen.

EPO's main function is to stimulate the production of red blood cells (RBCs) in the bone marrow. So as EPO levels rise, your bone marrow ramps up RBC production, and over the course of days to weeks, your total red blood cell mass increases. This leads to a sustained boost in hemoglobin, and with it, a more robust ability to deliver oxygen to your muscles and organs.

More EPO → More RBCs → More Hemoglobin in the blood = 

Greater oxygen-carrying capacity

This cascade is the cornerstone of altitude acclimatization. It’s why endurance athletes often train or live at high altitudes to naturally adapt the body to enhance oxygen transport capacity, which can give them an edge when returning to sea-level competition.

How Hemoglobin Holds the Key to Performance

Since most oxygen in the body is carried by hemoglobin, not simply dissolved in plasma, increasing hemoglobin concentration becomes a critical adaptation for maintaining endurance and recovery.

Source: Adapted from Houston, S., & Smith, J. University of Alberta.

Shown in the figure above, the body adapting to increase hemoglobin concentration helps compensate for reduced oxygen availability in the air, ensuring the body can continue to meet performance demands. Without an increase in hemoglobin, oxygen delivery to the muscles during training would fall by as much as 20%, seriously impacting endurance and recovery.

By increasing hemoglobin, the body can be trained to maintain nearly the same total oxygen content at altitude as it does at sea level, but only if adaptation occurs properly. That’s why monitoring these internal changes is key: it helps tailor altitude exposure, avoid overtraining, and ensure athletes get the full performance benefit.

But adaptation isn’t one-size-fits-all. Studies show individual responses to altitude can vary by up to 50% - meaning what works for one athlete may be completely ineffective for another. The key to unlocking altitude benefits? Real-time blood monitoring.

Why It’s Important to Track More Than Just Performance Metrics

Altitude training affects more than just perceived effort or external performance outputs. The internal, biological changes, especially those related to blood composition, are critical to understanding how well someone is adapting to altitude and how to tailor their training accordingly.

Key blood biomarkers include:

• Hemoglobin mass (Hbmass) change from baseline (%): A key indicator of the body’s capacity for oxygen transport and one of the most reliable long-term markers of adaptation.

• Hematocrit (HCT) change from baseline (%): Reflects the proportion of red blood cells in the blood, which can indicate either productive adaptation or dehydration-related concentration shifts.

• Red Blood Cell count (RBC): Measures the total number of oxygen-carrying cells. Increases typically correspond with enhanced aerobic performance potential.

• Plasma Volume change from baseline (%): Helps assess hydration status and early changes in blood concentration following altitude exposure.

• Reticulocyte proportion change from baseline (%): Represents the percentage of immature red blood cells in circulation, providing insight into the rate of new red blood cell production.

Monitoring these biomarkers enables a more accurate understanding of an athlete’s physiological state and helps in making informed decisions about training load, recovery, and altitude exposure duration.

The Future of Altitude Training

Altitude training is shifting from trial-and-error to precision. Where athletes once relied on how they felt, modern training now uses real-time biological data to guide performance. By tracking key blood biomarkers, especially hemoglobin mass, coaches can personalize altitude exposure, adjust training loads, and prevent overtraining. This approach helps athletes hit the sweet spot: enough hypoxic stress to trigger adaptation, without tipping into burnout.