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Soleus H-reflex dynamics during fast plantarflexion in humans
Masaki Fumoto1, Tomoyoshi Komiyama, Yoshiaki Nishihira
1Department of Physiology, Toho University School of Medicine, Tokyo, Japan.
Summary
The soleus Hoffmann (H-) reflex size changes dynamically during plantarflexion, showing a non-linear relationship with background electromyographic (EMG) activity. This suggests presynaptic inhibition is modulated by force level and movement phase.
Area of Science:
- Neuroscience
- Human Physiology
- Motor Control
Background:
- The Hoffmann (H-) reflex is a measure of Ia afferent nerve activity.
- Background electromyographic (EMG) activity influences H-reflex amplitude.
- Understanding H-reflex modulation is crucial for motor control research.
Purpose of the Study:
- To investigate the relationship between soleus H-reflex size and background EMG during plantarflexion.
- To examine how varying force levels affect this relationship.
- To explore the role of presynaptic inhibition in motor control.
Main Methods:
- Seven healthy males performed plantarflexion at 10%, 20%, 50%, and 80% MVC.
- Soleus H-reflex and M-wave amplitudes were recorded.
- Background EMG activity was monitored throughout the contractions.
Main Results:
- H-reflex size increased initially and then decreased during plantarflexion, irrespective of background EMG.
- H-reflex amplitude was larger during the rising than falling phase of EMG activity for the same background EMG level.
- H-reflex size showed poor correlation with exerted force, while F-response size was proportional to force.
Conclusions:
- The H-reflex exhibits a non-linear relationship with background EMG during plantarflexion.
- Presynaptic inhibition onto Ia terminals is modulated by force level and movement phase.
- These findings provide insights into the neural control of voluntary movements.