The effect of hypoxia on performance during 30 s or 45 s of supramaximal exercise

Summary

The purpose of this study was to evaluate the effect of hypoxia (10.8±0.6% oxygen) on performance of 30 s and 45 s of supramaximal dynamic exercise. Twelve males were randomly allocated to perform either a 30 s or 45 s Wingate test (WT) on two occasions (hypoxia and room air) with a minimum of 1 week between tests. After a 5-min warm-up at 120 W subjects breathed the appropriate gas mixture from a wet spirometer during a 5-min rest period. Resting blood oxygen saturation was monitored with an ear oximeter and averaged 97.8 ± 1.5% and 83.2 ± 1.9% for the air (normoxic) and hypoxic conditions, respectively, immediately prior to the WT. Following all WT trials, subjects breathed room air for a 10-min passive recovery period. Muscle biopsies from the vastus lateralis were taken prior to and immediately following WT. Arterialized blood samples, for lactate and blood gases, were taken before and after both the warm-up and the performance of WT, and throughout the recovery period. Opencircuit spirometry was used to calculate the total oxygen consumption (Vo₂), carbon dioxide production and expired ventilation during WT. Hypoxia did not impair the performance of the 30-s or 45-s WT.Vo₃ was reduced during the 45-s hypoxic WT (1.71±0.21 I) compared with the normoxic trial (2.16±0.261), but there was no change during the 30-s test (1.22±0.11 vs 1.04±0.171 for the normoxic and hypoxic conditions, respectively). Muscle lactate (LA) increased more during hypoxia following both the 30-s and 45-s WT (67.1±25.0 mmol· kg⁻¹ dry weight) compared with normoxia (30.8 ± 18.0 mmol · kg⁻¹ dry weight). Hypoxia did not influence the change in intramuscular adenosine triphosphate, creatine phosphate and glucose-6-phosphate. The performance of WT during hypoxia was associated with a greater decrease in muscle glycogen (P<0.06). Throughout the recovery period, blood LA was lower following the hypoxia (8.43±2.88 mmol · l⁻¹) comparedwith normoxia (9.15±3.06 mmol · 1⁻¹). Breathing the hypoxic gas mixture prior to the performance of WT increased blood pH to 7.44±0.03, compared with 7.39±0.03 for normoxia. Blood pH remained higher during the 10-min recovery period following the hypoxic WT trials (7.24±0.08) compared with the normoxic WT (7.22±0.06). BloodP _{CO 2} was reduced prior to and immediately following WT during hypoxia, but there were no differences between the normoxic and hypoxic trials during the 10 min recovery period. These data indicate that more energy was transduced from the catabolism of glycogen to lactate during the hypoxic WT trials, which offset the reduced O₂ availability and maintained performance comparable with normoxic conditions. It is suggested that the induced respiratory alkalosis associated with breathing the hypoxic gas could account for the increased rate of muscle LA accumulation.