Muscle sympathetic nerve activity in altitude acclimatized lowlanders during leg cycling exercise

Acute normobaric hypoxia augments muscle sympathetic nerve activity (MSNA) during dynamic cycling exercise; however, the effects of chronic hypobaric hypoxia exposure on this response remain unknown. The purpose of the present study was to determine MSNA reactivity to moderate intensity cycling exercise in lowlanders at sea‐level (344m; Kelowna, BC, Canada) and after 14–21 days of high‐altitude acclimatization (~4300m; Cerro de Pasco, Peru). MSNA (radial microneurography), mean arterial pressure (brachial artery catheter), and heart rate (electrocardiogram) were measured at rest and during cycling exercise (60% of peak workload) in six healthy male participants. Chronic exposure to hypobaric hypoxia increased resting MSNA burst frequency from 14.0 ± 3.2 burst/min at sea‐level, to 38.2 ± 4.5 burst/min (P<0.001). The increase in MSNA during semi recumbent cycling exercise during chronic hypobaric hypoxia exposure was significantly lower compared to sea‐level (Δ MSNA: sea‐level: 106 ± 46% vs. high‐altitude: 43 ± 15% vs; P<0.001). To our knowledge, this is the first investigation to compare MSNA between normobaric normoxia and chronic hypobaric hypoxia during leg cycling exercise. These data indicate that chronic hypobaric hypoxic exposure blunts the relative increase in MSNA during moderate‐intensity dynamic cycling exercise, potentially due to a sympathetic “ceiling” being reached. Support or Funding Information Wilderness Medical Society research in‐training grant (GM)