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15. 7. 2012.

Altitude: optimizing training and performance

Does altitude training improve sea-level performance?

Athletes have hypothesized for decades that training under hypoxic conditions, for example in an altitude chamber by simply breathing low-oxygen gas mixtures, can improve sea-level endurance performance. Since many of the beneficial changes associated with altitude acclimatization are similar to those conferred by aerobic training, can combining the two be even more beneficial? Can altitude training improve sea-level performance?
A strong theoretical argument can be made for altitude training. First, altitude training evokes substantial tissue hypoxia(reduced oxygen supply). This is thought to be essential for initiating the conditioning response. Second, the altitude-induced increase in red blood cell mass and hemoglobin levels improves oxygen delivery on return to sea level. Although evidence suggests that these latter changes are transient, lasting only several days, this still should provide an advantage for the athlete. Furthermore, studies from the 1960s and 1970s appeared to show that training at altitude did indeed enhance performance at sea level. Unfortunately, those studies did not test control groups who trained and competed at sea level, so it was impossible to tell whether the improved performance of the altitude-trained athletes was due to the training or the altitude.
More recent studies have shown that there is no additional benefit of living and training at altitude for increasing sea-level VO2max or improving sea-level performance. In addition, living at sea level and training in a hypobaric chamber to simulate altitude do not appear to provide any advantage over sea-level training. In the few studies in which altitude training was found to influence postaltitude sea-level performance, the subjects were not well trained before going to altitude. This makes it difficult to determine how much of their postaltitude improvement was attributable solely to training, independent of altitude.
Studying athletes as altitude poses additional problems because they are often unable to train at the same volume and intensity of effort as when at sea level. This was demonstrated in a group of elite female cyclists who performed self-selected maximum power outputs during high-intensity interval training. They completed trials under the following conditions: breathing atmospheric air(normoxia) and breathing a hypoxic gas mixture simulating 2,100m, or 6,888ft. The athletes’ sustained(10 min) and short-term(15s) power outputs at maximal intensity were reduced under hypoxic conditions. Training at even higher elevations, where acclimatization effects would be even more beneficial, causes even greater disruptions in training.
In addition, living and training at moderate to high altitude often causes athletes to dehydrate and to lose blood volume and muscle mass. These and other side effects tend to diminish the athletes’ fitness and their tolerance for intense training. As a result, studies are difficult to interpret, and the debate over the value of altitude training for optimal performance continues.

Optimizing performance at altitude

What can athletes who normally train at sea level but must compete at altitude do to prepare most effectively for competition? Although not all combinations have been attempted and research thus far is not conclusive, it appears that athletes have two viable options. One option is to compete as soon as possible after arriving at altitude, and certainly within 24h of arrival. This does not provide the beneficial effects of acclimatization, but the altitude exposure is brief enough that the classic symptoms of altitude sickness are not yet totally manifest. After the first 24h, the athlete’s physical condition often worsens because of the untoward effects of acute altitude exposure, such as dehydration, headache, and sleep disturbances.
Another option is to train at higher altitudes for a minimum of two weeks before competing. But not even two weeks is sufficient for total acclimatization. That would require a minimum of three to six weeks. Several weeks of intense aerobic training at sea level to increase the athletes VO2max will allow them to compete at altitude at a lower relative intensity(% VO2max) than if they had not trained aerobically.
Training for optimal adaptations at altitude requires an elevation between 1,500m(4,921ft), which is considered the lowest level at which an effect will be noticed, and 3,000m(9,840ft), which is the highest level for efficient conditioning. Work capacity is reduced during the initial days at altitude. For this reason, when first reaching higher altitudes, athletes should reduce workout intensity to between 60% and 70% of sea-level intensity, gradually working up to full intensity within 10 to 14 days.
Adaptations to altitude are generally responses to the hypoxia experienced there, so we might anticipate that people could achieve similar adaptations simply by breathing gases with a low PO2. But no evidence supports the idea that brief periods(1-2h per day) of breathing hypoxic gases or hypobaric mixtures induce even a partial adaptation similar to that observed at altitude. On the other hand, alternating periods(lasting between 5 and 14 days) of training at 2,300m(7,546ft) and at sea level adequately stimulated altitude acclimatization in group of elite middle-distance runners. Staying at sea level for up to 11 days did not interfere with the usual adjustments to altitude as long as training was maintained.

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