Muscle sympathetic nerve activity during handgrip and post-handgrip muscle ischemia after exposure to simulated microgravity in humans

Abstract To examine the effect of 6° head-down bed rest (HDBR) on vasomotor sympathetic responses to isometric forearm exercise, 16 healthy male subjects aged 20–36 years performed voluntary isometric handgrip (HG) at 30% of maximal voluntary contraction until fatigue, followed by 2 min of post-handgrip muscle ischemia (PHGMI) with 250 mmHg of cuff inflation, before and after 14 days of HDBR. Time to fatigue and maximal voluntary HG force were not affected by HDBR. Pre-exercise baseline muscle sympathetic nerve activity (MSNA, measured by microneurography), heart rate (measured by electrocardiogram) and mean blood pressure (measured by Portapres) increased after HDBR. Increases in MSNA were similar during HG but significantly lower during PHGMI ( P