![]() Microneurography is a technique that can be used to measure and record the electrical activity of the postganglionic sympathetic nerve. ![]() This review aimed to provide an updated comprehensive overview on the MSNA response to exercise including large-muscle, dynamic leg exercise, e.g., two-legged cycling, and its regulatory mechanisms in healthy humans. At that time, no data on the MSNA responses to dynamic leg exercise with large muscle mass were available. In 1991, Seals and Victor reviewed articles concerning MSNA responses to exercise in humans. These studies have revealed that the change in MSNA differs considerably depending on the exercise mode (static or dynamic), exercise intensity, duration of exercise, and environment (normoxia or hypoxia). Thereafter, numerous investigators have reported the MSNA response to exercise. ![]() reported, for the first time, an increase in muscle sympathetic nerve activity (MSNA) during sustained muscle contractions (handgrip and leg adduction). Therefore, direct measurement of sympathetic nervous activity is needed to provide more definitive insight into the effect of exercise. In addition, changes in plasma norepinephrine are progressing slowly, resulting in low time resolution. The main interpretive limitation of this measurement is that plasma levels are influenced by norepinephrine release and reuptake of norepinephrine. Alternations in sympathetic nerve activity during exercise have been inferred from changes in plasma norepinephrine concentrations. Central command (a feedforward mechanism originating from the cerebral cortex and/or subcortical nuclei), the exercise pressor reflex (a feedback mechanism originating from skeletal muscle, i.e., metaboreflex and mechanoreflex), the arterial baroreflex (a negative feedback mechanism originating from the carotid sinus and aortic arch), and cardiopulmonary baroreflex (a negative feedback mechanism originating from low-pressure mechanically sensitive stretch receptors located in the heart, vena cava and blood vessels of the lungs) work in concert creating complex interactions that regulate sympathetic vasomotor outflow during exercise. An appropriate regulation of sympathetic vasomotor outflow is key for maintaining arterial blood pressure and to facilitate the delivery of blood flow to active skeletal muscle. Precise cardiovascular and hemodynamic adjustments are necessary to meet the metabolic demand of active skeletal muscle. ![]()
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