Background muscle activity enhances the neuromuscular response to mechanical foot stimulation.
OBJECTIVE
The aim of the present study was to determine the modulating effect of background muscle activity on enhanced neuromuscular responses to mechanical foot stimulation.


METHODS
A small solenoid embedded within a platform provided nonnoxious stimulation to the lateral portion of the sole for 100 msecs at a 3-mm protrusion. The stimulation was applied during different contraction levels of the homonymous muscle and of remote, Jendrassik-like contractions. Peak amplitudes of the neuromuscular responses were measured from the soleus and lateral gastrocnemius muscles using root mean square electromyography.


RESULTS
Homonymous muscle contraction linearly increased peak amplitudes of the neuromuscular response induced by foot stimulation. Remote muscle contractions did not modulate the response. In all conditions, peak amplitudes of the reflex response reached 80-100% of maximal contraction levels. There was also a prolonged inhibition of homonymous contractions that lasted approximately 55 msecs after the excitatory neuromuscular response.


CONCLUSIONS
An application of mechanical foot stimulation enhanced neuromuscular activity of the triceps surae muscles; this enhancement was dependent on homonyomous background contraction levels.
Forth
Katharine Emily
KE
Laboratory of Integrated Physiology, University of Houston, Houston, Texas 77204-6015, USA.
Layne
Charles Shannon
CS
D000328:Adult; D004576:Electromyography; D005260:Female; D005528:Foot / Q000294:innervation / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009133:Muscular Atrophy / Q000534:rehabilitation*; D026201:Musculoskeletal Manipulations / Q000379:methods*; D010812:Physical Stimulation; D011446:Prospective Studies; D011999:Recruitment, Neurophysiological / Q000502:physiology*