Aerobic performance at altitude: effects of acclimatization and hematocrit with reference to training.

The aim of the present investigation carried out on six members of the Swiss 1981 Mt. Lhotse Shar (8398 m) expedition was to assess the quantitative role of some of the determinants of VO2max at altitude. The loss of VO2max expected for the investigated altitude range was partially counterbalanced by the training undergone by the subjects during the approach to the base camp. delta VO2max was -18% instead of the expected 30%-35%. The VO2max value attained shortly after arrival at 5200 m was not significantly increased (38.4 +/- 4.4 SD vs 36.9 +/- 3.3 ml O2.kg-1.min-1) with a progressive rise of Hb from 16.4 +/- 0.8 to 18.2 +/- 1 g/100 ml of blood. Hemodilution, by oral administration of 2 liters of the isosmolar solution ISOSTAR, at 5200 m led to a 2.3% decrease of Hct and a 7.3% reduction of VO2max per kg of body weight. The product of heart rate times systolic arterial pressure ("double product") was somewhat (but not significantly) greater in hypoxia than in normoxia at all work loads. The maximum value for this product, however, was 10%-15% lower at 5200 than at 400 m. The increase of Hb from 15.1 +/- 0.7 to 17.1 +/- 1.6 g/100 ml of blood pre- to post-expedition was not accompanied by a significant increase of VO2max determined at 400 m either absolute or per kg of body weight.