The effect of normocapnic hypoxia and the duration of exposure to hypoxia on supramaximal exercise performance

Summary

Two investigations were designed that (a) evaluated the effect of the respiratory alkalosis that accompanies breathing an hypoxic (H) gas mixture and (b) examined the influence of the duration of breathing this H mixture on the subsequent performance of 45 s supramaximal dynamic exercise. In experiment 1, 12 men performed a 45-s Wingate Test (WT) on three occasions breathing a normoxic (N; 20.9% 02), H (11.3% 02), or normocapnic hypoxic (H + CO₂; 11.5070 O₂, 2.25% CO₂) gas mixture for 20 min prior to performing the WT. For experiment 2, nine men performed a 20-min normoxic (N20) and three hypoxic WT trials which consisted of breathing an 11070 O₂ balance N₂ gas mixture for 10 min (H10), 20 min (H20) or 30 min (H30) prior to the WT. For experiment 1,VO₂ was significantly reduced during the 45-s H [mean (SD); 1.22 (0.23) 1] and H + CO₂ [1.12 (0.18)1] trials compared with the N trial [1.78 (0.18) 1]. Peak power output (W _peak) during WT was similar across trials. However, a small (less than 3070) but significant reduction in the mean power output (W) was observed in both the H and H + CO₂ trials [6.8 (0.6) W · kg⁻¹] compared with the N trial [7.0 (0.6) W · kg⁻¹]. Prior to performing the WT, blood pH andPCO₂ were similar [7.40 (0.02) and 5.3 (0.3) kPa, respectively] for the N and H + CO₂ trials. A respiratory alkalosis accompanied the H condition [7.46 (0.02) for pH and 4.6 (0.3) kPa forPCO₂. For experiment 2,VO₂ also was significantly lower during the 45-s WT for H10 [1.16 (0.16) 1], H2O [1.17 (0.16)1], and H30 [1.18 (0.26) 1] compared with N20 [1.84 (0.41) 1].W _peak was similar across trials but a significant reduction in meanW was observed again for the H trials [7.1 (0.4) W · kg⁻¹] compared with N20 [7.4 (0.4) W · kg⁻¹]. These data conflict with our previous findings and suggest that breathing an 11% H gas mixture will reduce the mean power produced during 45 s of supramaximal exercise.