Altitude Training Uncovered

There are many myths and misconceptions that surround the concept of altitude training within the disciplines of exercise physiology and sports training physiology. Such errors can lead to the misuse of training at altitude, which may lead to disappointment in subsequent performance. This article explores the subject of altitude training, defining what it is, acknowledging potential problems and its ultimate impact upon athletic performance.

Altitude training can be defined as training at heights greater than 2,500m above sea level. At such heights, it is commonly thought that there is a decreased percentage of atmospheric oxygen. However, the percentage of gases in the air we breathe remains unchanged from sea level to high altitude. Instead it is the partial pressure (PO₂) of each gas that is reduced as a drop in atmospheric pressure is seen at altitude. Therefore the air is less dense, consisting of less O₂, CO₂ and N₂ per litre, but the percentage of each gas forming this litre does not change. The fall in PO₂ reduces the driving pressure for gas exchange at the lungs, accordingly arterial O₂ saturations declines and so there is a rapid decline in O₂ availability to the working muscles. From near sea level, to a moderate altitude VO₂ max observes a linear reduction (Wehrlin and Hallen, 2006), on average this equates to -7.7% per 1000m of altitude despite a compensatory cardiorespiratory response.

It is this reduction in air density that can pose problems to training at altitude if an athlete is not fully prepared, one such consequence is a 1°C fall in temperature for each 100m ascent. The combination of a decreased temperature and pressure results in a reduced atmospheric water vapour content, which leads to increased respiration due to a decreased oxygen availability. This lends itself to greater water evaporation from the lungs, thus increasing the likelihood of severe dehydration that will inevitably cause a deterioration in athletic performance. As a result of these factors and a reduced cerebral O₂ saturation, many athletes suffer acute mountain sickness (AMS), the upshot of which leads to a lack of appetite, nausea, excessive weakness, vomiting and increased heart rate. Such symptoms dramatically impact upon the wellbeing of an athlete and in severe cases pulmonary or cerebral oedema can ensue. In order to prevent AMS a gradual introduction to altitude is needed, allowing for acclimation to occur which can take up to two weeks for heights of 2300m. This can be achieved through artificial means such as a hypoxic sleeping chamber or nitrogen generator to lower the atmospheric O₂ content.

An example of a hypoxic sleeping chamber. 

Within the realm of sport and exercise science there has been much debate as to whether the practice of altitude training can improve aerobic performance. It has been hypothesized that the compensatory physiological responses at altitude will result in adaptations that transfer to improved sea-level performance. However, this has been seen to be untrue. 

Altitude training has only been seen to cause performance improvements at altitude, with the majority of studies confirming that altitude endurance training fails to enhance sea-level performance. This outcome relates to the inability to perform at a sufficiently high intensity at altitude, at a height of 4000m exhaustion occurs at just 40% of sea level VO₂ max, thus failing to elicit the relevant aerobic physiological adaptations. However, the live high-train low rationale (Stray-Gundersen and Levine, 2008) provides hope for the significance of the inclusion of altitude for athletes. This theory states that the combined haematological adaptations from altitude and the maintenance of training intensity at sea level results in an improved endurance performance at sea level, giving leave to a 7.8% increase in O₂ carrying capacity. An adaptation such as this is achieved by increases in red blood cell mass, haemoglobin and erythropoietin, therefore increasing the delivery of oxygen to the working muscles.

Overall it has been shown that the combination of living high and training low can enhance sea level performance. This allows for a high training intensity to be maintained whilst also attaining the important haematological alterations that are associated with a high altitude.

References

Stray-Gundersen J., Levine B. D. (2008) Live high, train low at natural altitude. Scandinavian Journal of Medicine & Science in Sports. (1) pp. 21-28.

Wehrlin, J. P. and Hallen, J. (2006) Linear decrease in VO₂ max and performance with increasing altitude in endurance athletes. European Journal of Applied Physiology (96) pp. 404-412