PREACCLIMATIZATION TO HIGH-ALTITUDE USING EXERCISE WITH NORMOBARIC HYPOXIC GAS-MIXTURES

Pre-acclimatiztion was conducted using a new method elaborated in our laboratory, combining high intensity exercise while breathing hypoxia normobaric gas mixtures. The training consisted in a daily training during three weeks, 6 days a week, two hours a day, on bicycle ergometer. Eighteen subjects aging 22.2 +/- 1.4 years (11 males, 7 females) were matched in two similar groups: one group trained in normoxic conditions (NG) while the other group (HG) trained with a progressive decreae of the fraction of inspired oxygen (from 12.2% to 10.0%). Maximal oxygen uptake (VO2max) were measured before and after the protocol period in both hypoxic (VO2max H, FIO2 = 10.4%) and normoxic (VO2max N) conditions, for the 2 groups. Training induced a similar O2max N increase in the two groups. The ratio VO2Max H/VO2max N was calculated. As expected, in NG group, this ratio decreased significantly (from 63.9 +/- 4.3 to 57.5 +/- 3.1%, p < 0.01) after the training period compared to the initial value, diminution associated with an elevation Of VO2max N (from 48.4 +/- 9.0 to 52.9 +/- 9.0 ml.min-1.kg-1, p < 0.01). Conversely, in HG group, this ratio was not significantly diminished (from 61.7 +/- 3.8 to 60.5 +/- 5.2 %, NS) in spite of a similar increase of VO2max N (from 47.5 +/- 5.5 to 50.7 +/- 4.9 ml.min-1.kg-1, p < 0.01). This does not follow the diminution of the ratio usually described when VO2max N reach higher values. This difference between the decrease observed in NG as well as in the literature on one hand, and the absence of diminution observed in our HG group on the other hand, appears related to the training in hypoxia; the specific significant elevation of the Hypoxic Ventilatory Response (HVR) in HG group could be part of the particular adaptative process observed in this group. Furthermore, the stability of the ratio VO2max H/VO2max N in group HG does represent an important advantage when exposed to extreme conditions.