How High Altitude Affects Exercise

Male runner exercising at high altitude with mountains in the background.
At high altitudes there is significantly less oxygen pressure in the atmosphere which subsequently decreases aerobic capacity in non-acclimatized individuals.

Hemoglobin plays a crucial role in the transportation of oxygen. The pressure of oxygen in blood determines how much O2 is bound to hemoglobin. The oxyhemoglobin dissociation curve represents the percentage of O2 saturation of hemoglobin at varying oxygen pressures. Two of the biggest factors affecting blood oxygen pressure are exercise intensity and geographic altitude.

At sea level, resting O2 saturation is normally between 97% – 99% in healthy individuals and is represented by the upper/right-most point on the curve (Fig. 1). At elevations of 9800 ft. (3000m), O2 sat can drop to 89%. If you find yourself at the peak of Mt. Everest, it can drop down to 40%!

As altitude increases or exercise intensity increases, partial pressure of oxygen (PaO2) decreases as a result. In response to this lowered oxygen pressure, hemoglobin releases more bound O2. It is apparent that the dissociation curve follows a curvilinear, downward direction (Fig. 1) as exercise intensity/altitude increases (the green arrow represents the trend of decreasing O2 saturation and pressure as exercise intensity or altitude increases).

Graph explains effect of high altitude on endurance training.
Figure 1. Oxyhemoglobin dissociation curve

When maximal exertion and exhaustion occurs, PaO2 can reach levels of 2-3 mmHg with hemoglobin giving up nearly all of its oxygen. The more complete unloading of hemoglobin-bound oxygen as exercise intensity increases aids in delivering O2 to the working muscles. Since the body’s O2 transport systems work efficiently in providing tissue with oxygen, even during intense exercise, the limitations in aerobic capacity result from lack of adequate oxygen supply in the blood.

Immediate Effect of High Altitude on Endurance and Anaerobic Exercise

The partial pressure of oxygen decreases as altitude increases. This decrease in air density with altitude poses physiologic problems for non-acclimatized individuals, especially during aerobic exercise. Acute exposure to altitudes 2500 m or greater most noticeably induces hyperventilation. Altitude-induced arterial hypoxia as a result of reduced PaO2 triggers physiologic changes that are responsible for the acute and long-term adjustments to increased land elevation.

A person at sea level, where PaO2 is 100 mmHg, will have a 98% O2 saturation. However, at 3048 m above sea level where PO2 is 78 mmHg, O2 saturation drops to 89 – 90% as mentioned above. At rest or mild exertion, this change has little effect on the individual. However, aerobic activity longer than 2.5 minutes will result in poor performance in the non-acclimatized individual. This decreased aerobic performance can be seen a result of decreased oxygen capacity.

Furthermore, immediate cardiovascular response to exercise for this individual would involve increased submaximal HR and submaximal cardiac output. At moderate altitude (2500 m) the anaerobic performance of the unacclimatized individual will not suffer. Performance in one-off anaerobic events such as sprinting can actually improve due to lesser air density creating less drag resistance.

Check out Physiological Responses to Altitude by Frank Wyatt, PhD for more information on how high elevation effects your body and the adaptations that take place (acclimatization).