What did the Levine and Stray-Gundersen research actually measure?
Their study tested whether living at a moderate altitude of 2,500 meters while training at a lower altitude of 1,250 meters improved sea-level performance more than training entirely at sea level or entirely at altitude. The result was an average sea-level performance improvement of about 1.5 percent, with individual responses ranging from no benefit at all up to a 6 percent gain, and the improvement lasting at least three weeks after athletes returned to sea level. The researchers tied the effect to an 8 percent increase in red cell volume among the group that lived high and trained low, which correlated with the gains they saw in VO2max, the standard measure of maximal oxygen uptake. That correlation, not just the headline percentage, is what turned the study into a reference point for exercise physiologists rather than a one-off finding.
