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Sympathetic activation is associated with increases in EMG during fatiguing exercise
1Department of Exercise and Sport Sciences, University of Arizona, Tucson 85721.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|January 1, 1989
Summary
Sympathetic nerve activity increases with muscle fatigue during prolonged exercise. This study shows a direct relationship between muscle sympathetic nerve activity and the development of fatigue, impacting exercise adjustments.
Area of Science:
- Exercise Physiology
- Autonomic Nervous System Function
- Skeletal Muscle Physiology
Background:
- Muscle fatigue is a common outcome of prolonged exercise.
- The role of the sympathetic nervous system during exercise-induced fatigue is not fully understood.
- Previous research has not clearly established the link between sympathetic neural discharge and muscle fatigue development.
Purpose of the Study:
- To investigate the hypothesis that efferent sympathetic neural discharge is coupled with muscle fatigue during voluntary exercise in humans.
- To determine if sympathetic activation correlates with the development of fatigue during isometric handgrip exercise.
- To examine how repeated fatiguing contractions affect sympathetic neural adjustments during exercise.
Main Methods:
- 12 healthy subjects performed submaximal isometric handgrip exercise to exhaustion.
- Measured heart rate, arterial blood pressure, and muscle sympathetic nerve activity (MSNA) in the peroneal nerve.
- Recorded electromyographic (EMG) activity of the exercising forearm in a subset of participants.
Main Results:
- Heart rate and arterial blood pressure increased significantly within the first minute of exercise.
- Muscle sympathetic nerve activity (MSNA) and EMG activity did not increase significantly in the first minute but rose progressively thereafter.
- A strong positive correlation (r=0.85) was found between MSNA and EMG activity, indicating a parallel increase.
- Subsequent exercise trials showed greater increases in HR, AP, MSNA, and EMG at any given time point.
Conclusions:
- Sympathetic activation to non-contracting skeletal muscle is directly related to the development of muscle fatigue during prolonged isometric exercise.
- Previous fatiguing contractions alter the time course of sympathetic neural adjustments during exercise.
- Findings suggest a significant coupling between autonomic nervous system responses and the progression of muscle fatigue.