Microneurographic studies of the mechanisms of sympathetic nerve responses to static exercise in humans.

Abstract

The purpose of this study was to determine the contribution of muscle afferents and central command in regulating sympathetic nerve activity during static exercise in humans. In 20 healthy subjects, we recorded heart rate, arterial pressure, and efferent sympathetic nerve activity in the leg during arm exercise. Microelectrodes were inserted percutaneously into a fascicle of the peroneal nerve to measure sympathetic discharge to muscle. Measurements were obtained in nine subjects during sustained handgrip (30% maximal voluntary contraction) followed by relaxation or by arrested circulation of the forearm. Heart rate and arterial pressure increased during the first and second minutes of handgrip. Muscle sympathetic nerve activity increased from 261 +/- 46 to 504 +/- 97 units (mean +/- SE; units = burst frequency X amplitude; P less than 0.05) during the second minute of handgrip. During forearm ischemia following handgrip, heart rate returned promptly to control, whereas arterial pressure and muscle sympat...