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Changes in motor cortical excitability during human muscle fatigue
J L Taylor1, J E Butler, G M Allen
1Prince of Wales Medical Research Institute, Randwick, NSW, Australia.
The Journal of Physiology
|January 15, 1996
Summary
Motor cortex excitability changes during fatiguing contractions. Findings suggest increased excitation and inhibition within the motor cortex, independent of sensory input, during sustained maximal efforts.
Area of Science:
- Neuroscience
- Human Physiology
- Motor Control
Background:
- Motor cortex excitability is crucial for voluntary movement.
- Understanding how motor cortex function changes during fatigue is essential for rehabilitation and performance optimization.
Purpose of the Study:
- To investigate changes in motor cortex excitability during fatiguing elbow flexor contractions.
- To determine the role of afferent feedback in modulating these cortical changes.
Main Methods:
- Transcranial magnetic stimulation (TMS) was used to assess motor cortex excitability during sustained submaximal and maximal voluntary contractions.
- Electromyography (EMG) recorded muscle responses.
- Blood flow occlusion and tendon vibration were employed to manipulate afferent input.
Main Results:
- TMS-evoked EMG responses and silent periods in elbow flexors changed during sustained maximal voluntary contractions (MVCs).
- These changes were not observed during submaximal contractions or in a non-fatigued muscle.
- Blocking blood supply or using tendon vibration did not alter the fatigue-related changes in cortical excitability, suggesting they are not mediated by peripheral sensory feedback.
Conclusions:
- Fatigue during sustained MVCs leads to altered motor cortex excitability, characterized by increased excitation and inhibition.
- These cortical changes appear to be intrinsic to the motor cortex, rather than driven by altered afferent input.
- Findings suggest intrinsic cortical mechanisms and altered voluntary drive contribute to motor cortex changes during fatigue.