We hypothesize that plasma volume decrease (ΔPV) induced by high-altitude (HA) exposure and intense exercise is involved in the limitation of maximal O2 uptake (V˙o2 max) at HA. Eight male subjects were decompressed for 31 days in a hypobaric chamber to the barometric equivalent of Mt. Everest (8,848 m). Maximal exercise was performed with and without plasma volume expansion (PVX, 219–292 ml) during exercise, at sea level (SL), at HA (370 mmHg, equivalent to 6,000 m after 10–12 days) and after return to SL (RSL, 1–3 days). Plasma volume (PV) was determined at rest at SL, HA, and RSL by Evans blue dilution. PV was decreased by 26% ( P < 0.01) at HA and was 10% higher at RSL than at SL. Exercise-induced ΔPV was reduced both by PVX and HA ( P < 0.05). Compared with SL, V˙o2 max was decreased by 58 and 11% at HA and RSL, respectively.V˙o2 max was enhanced by PVX at HA (+9%, P < 0.05) but not at SL or RSL. The more PV was decreased at HA, the moreV˙o2 max was improved by PVX ( P < 0.05). At exhaustion, plasma renin and aldosterone were not modified at HA compared with SL but were higher at RSL, whereas plasma atrial natriuretic factor was lower at HA. The present results suggest that PV contributes to the limitation ofV˙o2 max during acclimatization to HA. RSL-induced PVX, which may be due to increased activity of the renin-aldosterone system, could also influence the recovery ofV˙o2 max.
656 BIOELECTRICAL IMPEDANCE ANALYSIS (BI): ROLE OF PLASMA VOLUME EXPANSION IN THE VALIDITY OF BODY COHPOSITION IN LEAN MALES