The purpose of this study was to determine whether the metabolic response and running performance during intermittent graded sprint running were affected by moderate hypobaric hypoxia (H; 2,500 m above sea level) in competitive middle-distance runners. Nine male runners performed intermittent graded sprint running until exhaustion, to evaluate the metabolic response and running performance in H and normobaric normoxia (N). The test constructed of incremental (25 m min-1) 20 s running bouts (4° inclination) interspaced with 100 s recovery periods. Maximal running speed was not different between conditions [453 (7) m min-1 vs. 458 (4) m min-1 in N vs. H]. V\textO2VO2 at each speed was lower in H than N (ANOVA; P < 0.05). Although, oxygen deficit (D\textO2 )DO2 at each speed was not different between N and H (ANOVA; P = 0.1), total accumulated D\textO2DO2 in all bouts was significantly higher in H than N [165 (10) ml kg-1 in N and 173 (10) ml kg-1 in H]. The ratio of D\textO2·V\textO2-1DO2VO2-1 was similar in all bouts, but higher in H than N. These results suggest that intermittent graded sprint running performance is not affected by moderate hypobaria despite a reduction in the energy supplied by aerobic metabolism due to a compensatory increase in the energy supplied by the anaerobic metabolism in competitive middle-distance runners.
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