ALTITUDE TRAINING: WHO BENEFITS?
Smith, M. H., & Sharkey, B. J. (1984). Altitude training: who benefits? The Physician and Sportsmedicine, 12, 48-62.
Studies at moderate altitude are not conclusive in demonstrating a beneficial training effect for talented athletes who are already fully trained. Limitations are inherent in conclusions drawn from studies done at various altitudes [because varying degrees of stress invoke different forms of adaptation.]
Responses. When the body is subjected to a hypoxic environment, adaptive processes attempt to facilitate the intake, transport, and use of oxygen.
Opinions differ as to whether cardiac output is initially elevated or unchanged.
Cardiac output is reduced when compared to sea-level variables several days to weeks after exposure primarily through a reduced stroke volume. Once depressed, cardiovascular function remains depressed and does not recover with increasing length of exposure.
Hematological adjustments occur to augment the oxygen content of the blood. Hemoglobin concentration increases as the plasma volume decreases. RBCs increase due to a hypoxic-sensitive erythropoietic mechanism that alters HB and hematocrit values. The greater circulating volume of Hb increases the oxygen-carrying capacity of the blood.
Maximum aerobic power (VO2max) is a function of cardiac output and arteriovenous oxygen difference. The changes that occur raise the question of whether the altered conditions would increase sea-level performance because of the supranormal condition. The work in this area is conflicting.
Better studies that employ control groups and design considerations do not support any beneficial effect. This has been reported on swimmers:
"One of the major problems with these early studies was the lack of a control group, where an equivalent group underwent the same training program at sea-level. Without a control group, it is difficult to separate an improvement in fitness and performance caused by training from the possible potentiating effects of altitude." (p. 54)
The main difficulty is getting a good control group that is matched on critical potential confounding variables. In one study, one leg was trained at altitude, the other at sea-level in highly trained runners. Thus, subjects served as their own controls. No benefit from altitude was found. [Adams, W. C., Bernauer, E. M., Dill, D. B., & Bomar, J. B. (1975). Effects of equivalent sea-level and altitude training on VO2max and running performance. Journal of Applied Physiology, 39, 262-266.]
Individual response. Statistical analyses of groups may not be the most sensitive tests of effects. It is strongly supported in the literature that some individuals are assisted by altitude training while others are not and even some regress because of the stressful exposure.
The generalization of laboratory measurements to performance potential is also a source of error. The predictive reliability of laboratory physiological measures is not high. The question arises that in the few who seem to be benefited by altitude exposure what are the mechanisms?
"A critical reading of the literature casts doubt on the value of altitude training, at least for some athletes." (p. 59)
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