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Central command increases muscle sympathetic nerve activity during intense intermittent isometric exercise in humans
R G Victor1, N H Secher, T Lyson
1Copenhagen Muscle Research Center, Department of Anaesthesia, Rigshospitalet, University of Copenhagen Denmark.
Circulation Research
|January 1, 1995
Summary
Central command significantly impacts muscle sympathetic nerve activity (MSNA) during intense intermittent exercise. This neural control synchronizes muscle sympathetic activity with motor commands, even when force output is reduced.
Area of Science:
- Exercise Physiology
- Neuroscience
- Autonomic Nervous System
Background:
- Central command's influence on muscle sympathetic nerve activity (MSNA) is minimal during sustained isometric exercise.
- The effect of central command on MSNA during intermittent contractions remains less understood.
Purpose of the Study:
- To investigate the impact of central command on MSNA during intermittent isometric handgrip exercise.
- To differentiate the effects of central command from muscle afferent feedback on MSNA.
Main Methods:
- Muscle sympathetic nerve activity (MSNA) was recorded using microelectrodes in the peroneal nerve.
- Intermittent isometric handgrip contractions were performed at varying intensities (25%, 50%, 75% MVC) with paced breathing.
- Neuromuscular blockade (curare) was used to isolate central command's influence by minimizing voluntary force output.
Main Results:
- At 75% MVC, handgrip synchronized MSNA, increasing it significantly during contraction periods compared to relaxation periods.
- This synchronization persisted even after neuromuscular blockade reduced force output to below 25% of initial MVC.
- Lower intensities (25%, 50% MVC) did not affect MSNA.
Conclusions:
- Central command is a primary driver for the synchronization of motor and muscle sympathetic activity during intense intermittent isometric exercise.
- This finding highlights a specific neural mechanism linking central motor commands to autonomic outflow during dynamic physical exertion.