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Reciprocal inhibition versus unloading response during stretch reflex in humans
C D Manning1, P L L McDonald, C D Murnaghan
1Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC V5A 1S6, Canada.
Experimental Brain Research
|January 29, 2013
Summary
This study investigated muscle activity during joint rotation. Findings suggest that decreased antagonist muscle activity results from active inhibition, not just unloading, indicating complex reflex pathways.
Area of Science:
- Neuroscience
- Human Physiology
- Biomechanics
Background:
- Joint rotation elicits stretch reflexes (M1, M2) in stretched muscles.
- Simultaneously, shortened antagonist muscles show decreased electromyographic (EMG) activity (rINHIB).
Purpose of the Study:
- To determine if decreased antagonist muscle activity (rINHIB) is solely due to spindle unloading.
- To investigate the role of active inhibition via inhibitory interneurons in rINHIB.
Main Methods:
- Used a torque motor to apply rectangular rotational pulses (25-150 ms) to wrist flexors/extensors.
- Measured joint rotation peak times (T(peak) 75-160 ms) and EMG activity termination in antagonist muscles.
Main Results:
- Stretch reflex M1 magnitude remained constant with shorter rotation durations.
- Stretch reflex M2 magnitude decreased with shorter rotation durations.
- Termination time of rINHIB in shortened muscles was independent of T(peak).
Conclusions:
- The consistent termination time of rINHIB suggests active inhibitory reflex pathways contribute to decreased antagonist muscle activity.
- Unloading of antagonist muscle spindles alone does not fully explain the observed EMG reductions.
- Short- and long-latency inhibition mechanisms are implicated in regulating antagonist muscle activity during joint rotation.
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