The aim of this study was to clarify the sympathetic nerve activity and cardiovascular response to dynamic exercise following hypoxic exposure. We determined muscle sympathetic nerve activity (MSNA), heart rate (HR), and arterial blood pressure (BP) during leg cycle exercise after hypoxic exposure, and compared these variables during exercise without hypoxic exposure. MSNA was measured from the right median nerve using the microneurographic technique. The experiments were performed on 2 separate days as the following, 1) baseline at rest for 5 min in normoxia, 2) breathing hypoxic or normoxic gas mixture at rest for 20 min (arterial O₂ saturation, 77.5±1.4% in hypoxia and 96.5±1.6% in normoxia, mean±SE), 3) breathing normoxic gas at rest for 10 min, 4) two consecutive 10-min exercises using the bicycle ergometer at 40% and 70% of peak oxygen uptake (VO₂peak) in normoxia. Hypoxic exposure led to significant (P<0.05) increases in minute ventilation (VE), HR, MSNA burst frequency (MSNA BF). VE and HR returned to baseline levels after the cessation of hypoxia, whereas hypoxiainduced increased MSNA BF persisted after the return to normoxia. During leg cycle exercise, MSNA BF increased significantly (P<0.05), but the magnitude of the increased MSNA BF following hypoxic exposure did not differ from that without hypoxic exposure. There were no significant differences in HR and BP responses to cycle exercise with or without prior hypoxic exposure. These results suggest that prior short-term hypoxic exposure does not affect to the sympathetic nerve activity and cardiovascular response to exercise.

DESCENTE SPORTS SCIENCE Vol.30/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE