Hypoxia affects tissue oxygenation differently in the thigh and calf muscles during incremental running.

<bold>Purpose: </bold>The present study was performed to determine the impact of hypoxia on working muscle oxygenation during incremental running, and to compare tissue oxygenation between the thigh and calf muscles.<bold>Methods: </bold>Nine distance runners and triathletes performed incremental running tests to exhaustion under normoxic and hypoxic conditions (fraction of inspired oxygen = 0.15). Peak pulmonary oxygen uptake ([Formula: see text]) and tissue oxygen saturation (StO2) were measured simultaneously in both the vastus lateralis and medial gastrocnemius.<bold>Results: </bold>Hypoxia significantly decreased peak running speed and [Formula: see text] (p < 0.01). During incremental running, StO2 in the vastus lateralis decreased almost linearly, and the rate of decrease from warm-up (180 m min-1) to [Formula: see text] was significantly greater than in the medial gastrocnemius under both normoxic and hypoxic conditions (p < 0.01). StO2 in both muscles was significantly decreased under hypoxic compared with normoxic conditions at all running speeds (p < 0.01). The rate at which StO2 was decreased by hypoxia was greater in the vastus lateralis as the running speed increased, whereas it changed little in the medial gastrocnemius.<bold>Conclusions: </bold>These results suggest that the thigh is more deoxygenated than the calf under hypoxic conditions, and that the effects of hypoxia on tissue oxygenation differ between these two muscles during incremental running. [ABSTRACT FROM AUTHOR]