Graded leg cycling at 20% VO2max suppressed MSNA burst frequency by 28% (23 vs. 33 bursts/min for control), with linear increases at higher exercise intensities.
Does graded leg cycling alter muscle sympathetic nerve activity in healthy volunteers?
Light exercise suppresses muscle sympathetic nerve activity, likely due to baroreflex inhibition, while heavier exercise increases it via muscle metaboreflex activation.
Effect estimate: 28% suppression
Absolute Event Rate: 23% vs 33%
The aim of this study was to clarify the relationship between sympathetic outflow to skeletal muscle and oxygen uptake during dynamic exercise. Muscle sympathetic nerve activity (MSNA) was recorded from the right median nerve microneurographically in eight healthy volunteers during leg cycling at four different intensities in a seated position for a 16-min bout. Work loads selected were 20, 40, 60, and 75% of maximal oxygen uptake (VO2max). Heart rate and blood pressure were measured during each exercise test. MSNA burst frequency was suppressed by 28% during cycling at 20% VO2max (23 vs. 33 bursts/min for control). Thereafter, it increased in a linear fashion with increasing work rate, with a significantly higher burst frequency during 60% VO2max than the control value. Both heart rate and mean blood pressure rose significantly during 20% VO2max from the control value and increased linearly with increased exercise intensity. During light exercise, MSNA was suppressed by arterial and cardiopulmonary baroreceptors as a result of the hemodynamic changes associated with leg muscle pumping. The baroreflex inhibition may overcome the muscle metaboreflex excitation to induce MSNA suppression during light exercise. These results suggest that during light exercise MSNA is inhibited, perhaps due to loading of the cardiopulmonary and arterial baroreflexes, and that during heavier exercise the increase in MSNA occurs as muscle metaboreflexes are activated.
Saito et al. (Sun,) conducted a other in Healthy (n=8). Graded leg cycling vs. Control was evaluated on Muscle sympathetic nerve activity (MSNA) burst frequency (28% suppression). Graded leg cycling at 20% VO2max suppressed MSNA burst frequency by 28% (23 vs. 33 bursts/min for control), with linear increases at higher exercise intensities.