Department of Human Health and Nutritional Sciences, University of Guelph , Guelph, Ontario , Canada.
Department of Kinesiology, University of Guelph-Humber , Toronto, Ontario , Canada.
Am J Physiol Heart Circ Physiol. 2018 Jan 1;314(1):H3-H10. doi: 10.1152/ajpheart.00494.2017. Epub 2017 Sep 22.
The contribution of central command to the peripheral vasoconstrictor response during exercise has been investigated using primarily handgrip exercise. The purpose of the present study was to compare muscle sympathetic nerve activity (MSNA) responses during passive (involuntary) and active (voluntary) zero-load cycling to gain insights into the effects of central command on sympathetic outflow during dynamic exercise. Hemodynamic measurements and contralateral leg MSNA (microneurography) data were collected in 18 young healthy participants at rest and during 2 min of passive and active zero-load one-legged cycling. Arterial baroreflex control of MSNA burst occurrence and burst area were calculated separately in the time domain. Blood pressure and stroke volume increased during exercise ( P < 0.0001) but were not different between passive and active cycling ( P > 0.05). In contrast, heart rate, cardiac output, and total vascular conductance were greater during the first and second minute of active cycling ( P < 0.001). MSNA burst frequency and incidence decreased during passive and active cycling ( P < 0.0001), but no differences were detected between exercise modes ( P > 0.05). Reductions in total MSNA were attenuated during the first ( P < 0.0001) and second ( P = 0.0004) minute of active compared with passive cycling, in concert with increased MSNA burst amplitude ( P = 0.02 and P = 0.005, respectively). The sensitivity of arterial baroreflex control of MSNA burst occurrence was lower during active than passive cycling ( P = 0.01), while control of MSNA burst strength was unchanged ( P > 0.05). These results suggest that central feedforward mechanisms are involved primarily in modulating the strength, but not the occurrence, of a sympathetic burst during low-intensity dynamic leg exercise. NEW & NOTEWORTHY Muscle sympathetic nerve activity burst frequency decreased equally during passive and active cycling, but reductions in total muscle sympathetic nerve activity were attenuated during active cycling. These results suggest that central command primarily regulates the strength, not the occurrence, of a muscle sympathetic burst during low-intensity dynamic leg exercise.
目前的研究旨在比较被动（非自愿）和主动（自愿）零负荷单腿循环期间肌肉交感神经活动（MSNA）的反应，以深入了解中枢命令对动态运动期间交感神经输出的影响。在 18 名年轻健康的参与者中，在休息时和被动和主动零负荷单腿循环的 2 分钟内收集血流动力学测量和对侧腿部 MSNA（微神经记录）数据。分别在时域中计算 MSNA 爆发发生和爆发面积的动脉压力反射控制。血压和每搏量在运动时增加（P <0.0001），但在被动和主动循环之间没有差异（P> 0.05）。相反，在主动循环的第一分钟和第二分钟，心率、心输出量和总血管传导率较高（P <0.001）。MSNA 爆发频率和发生率在被动和主动循环期间降低（P <0.0001），但在运动模式之间没有差异（P> 0.05）。与被动循环相比，主动循环的第一分钟（P <0.0001）和第二分钟（P = 0.0004）时，总 MSNA 的减少被减弱，同时 MSNA 爆发幅度增加（P = 0.02 和 P = 0.005）。与被动循环相比，主动循环时动脉压力反射对 MSNA 爆发发生的控制敏感性较低（P = 0.01），而 MSNA 爆发强度的控制不变（P> 0.05）。这些结果表明，中枢前馈机制主要参与调节低强度动态腿部运动期间交感神经爆发的强度，但不参与调节爆发的发生。
