AUTHOR=Sumi Daichi , Kasai Nobukazu , Ito Hiroto , Goto Kazushige 

TITLE=The Effects of Endurance Exercise in Hypoxia on Acid-Base Balance, Potassium Kinetics, and Exogenous Glucose Oxidation

JOURNAL=Frontiers in Physiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2019.00504

DOI=10.3389/fphys.2019.00504

ISSN=1664-042X

ABSTRACT=<sec><title>Purpose</title><p>To investigate the carbohydrate metabolism, acid–base balance, and potassium kinetics in response to exercise in moderate hypoxia among endurance athletes.</p></sec><sec><title>Methods</title><p>Nine trained endurance athletes [maximal oxygen uptake (VO<sub>2max</sub>): 62.5 ± 1.2 mL/kg/min] completed two different trials on different days: either exercise in moderate hypoxia [fraction of inspired oxygen (FiO<sub>2</sub>) = 14.5%, HYPO] or exercise in normoxia (FiO<sub>2</sub> = 20.9%, NOR). They performed a high-intensity interval-type endurance exercise consisting of 10 × 3 min runs at 90% of VO<sub>2max</sub> with 60 s of running (active rest) at 50% of VO<sub>2max</sub> between sets in hypoxia (HYPO) or normoxia (NOR). Venous blood samples were obtained before exercise and during the post-exercise. The subjects consumed <sup>13</sup>C-labeled glucose immediately before exercise, and we collected expired gas samples during exercise to determine the <sup>13</sup>C-excretion (calculated as <sup>13</sup>CO<sub>2</sub>/<sup>12</sup>CO<sub>2</sub>).</p></sec><sec><title>Results</title><p>The running velocities were significantly lower in HYPO (15.0 ± 0.2 km/h) than in NOR (16.4 ± 0.3 km/h, <italic>P</italic> &lt; 0.0001). Despite the lower running velocity, we found a significantly greater exercise-induced blood lactate elevation in HYPO compared with in NOR (<italic>P</italic> = 0.002). The bicarbonate ion concentration (<italic>P</italic> = 0.002) and blood pH (<italic>P</italic> = 0.002) were significantly lower in HYPO than in NOR. There were no significant differences between the two trials regarding the exercise-induced blood potassium elevation (<italic>P</italic> = 0.87) or <sup>13</sup>C-excretion (HYPO, 0.21 ± 0.02 mmol⋅39 min; NOR, 0.14 ± 0.03 mmol⋅39 min; <italic>P</italic> = 0.10).</p></sec><sec><title>Conclusion</title><p>Endurance exercise in moderate hypoxia elicited a decline in blood pH. However, it did not augment the exercise-induced blood K<sup>+</sup> elevation or exogenous glucose oxidation (<sup>13</sup>C-excretion) compared with the equivalent exercise in normoxia among endurance athletes. The findings suggest that endurance exercise in moderate hypoxia causes greater metabolic stress and similar exercise-induced elevation of blood K<sup>+</sup> and exogenous glucose oxidation compared with the same exercise in normoxia, despite lower mechanical stress (i.e., lower running velocity).</p></sec>