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POINT-COUNTERPOINT
Levine and Stray-Gundersen focused on the association between maximum oxygen consumption (
O2max), red cell volume (RCV), and performance by splitting subjects into responders and nonresponders based on change in time trial performance. Responders had bigger changes in O2max and RCV than nonresponders, but these differences could be due at least partly to the responders’ higher intensity of interval training or to fluctuations in RCV unrelated to altitude exposure. Levine and Stray-Gundersen also used a model to argue that the changes in RCV and hemoglobin concentration accounted accurately for the changes in O2max in the two groups. The accuracy is probably accidental, because this model does not accurately predict the changes in one or more of their altitude groups (3).
Levine and Stray-Gundersen provided two references (3, 5) for their claim that "economy never changed" in their research on "n > 100" runners. Reference 5 is an early review in which we could find no assertions or data for changes in economy, despite exhaustive searching of all the references (mostly conference abstracts) therein. Reference 3 is a study in which there were no statistically significant differences in change in economy between a control and two attitude groups, each of 13 runners. Confidence limits for the changes would presumably be consistent with real improvements of 
1-2% after altitude training. We can think of no other straightforward way to reconcile this study with the six studies we cited showing clear-cut improvements in economy.
We grant Levine and Stray-Gundersen some stimulation of erythropoiesis, especially at high altitude, but its contribution to performance enhancement is unclear. They claim that low doses of exogenous erythropoietin produce effects on RCV that are virtually identical to those of altitude training, whereas other researchers (1) have shown that high doses of erythropoietin are needed to produce the large changes in RCV that Levine and Stray-Gundersen report.
Finally, Levine and Stray-Gundersen’s claim that low iron stores prevent altitude-associated performance enhancement of O2max and performance would be their best evidence, were true. A low iron store unquestionably prevents an increase in RCV, but astonishingly, neither reference cited to support their claim (2, 7) included data on O2max or performance. Similarly, the reference for their claim that infection inhibits erythropoiesis and prevents an increase in O2max or performance (8) actually only suggests the possibility, based on other studies, of erythropoiesis and only in tissue cultures and animals. Even their claim that "no other effects of altitude acclimatization... can be manipulated independently... to improve athletic performance" is wrong: some kinds of resistance training enhance endurance performance by increasing economy selectively (6).
In summary, the evidence presented by Levine and Stray-Gundersen is consistent with an unclear role for erythropoiesis, RCV, and O2max in the effects of altitude training on endurance performance. The role of the only plausible alternative, exercise economy, is also unclear. Furthermore, a fall in fractional utilization could partially or completely offset the effects of increases in O2max and economy. We therefore repeat our call for more research to clarify the relative contribution of these three aerobic determinants of endurance in altitude studies.
REFERENCES
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