Exercise mode affects muscle sympathetic nerve responsiveness

To compare the responses of remote sympathetic nerves to dynamic and static leg exercises, we recorded sympathetic nerve activity leading to skeletal muscle (MSNA) using a tungsten microelectrode during one-leg cycling at loads of 0, 25, and 50 W and during static leg extension (SLE) at 20% of maximal voluntary contraction. Oxygen uptake (Douglas bag method) and local fatigue sensation (LFS) of the working muscle were measured during cycling and SLE. MSNA decreased from the control value, respectively, by 25, 21, and 12% during cycling at loads of 0, 25, and 50 W. The differences from the control value were significant except during cycling at 50 W. On the contrary, MSNA increased from the control value by 83% during SLE. Oxygen uptake during 25 and 50 W leg cycling was greater than during SLE, whereas LFS was higher during SLE than during leg cycling at any load. The results indicate that the response of muscle sympathetic nerves to exercise does not exclusively reflect whole body metabolism, but is instead related to the local metabolic changes.