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Surface potentials generated by synchronous activation of different fractions of the motor pool
Author(s) -
Hughes A.R.,
Colebatch J.G.
Publication year - 1996
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/(sici)1097-4598(199607)19:7<836::aid-mus4>3.0.co;2-a
Subject(s) - compound muscle action potential , tonic (physiology) , reflex , electrophysiology , stimulus (psychology) , amplitude , chemistry , anatomy , f wave , evoked potential , neuroscience , psychology , physics , medicine , nerve conduction velocity , quantum mechanics , psychotherapist
Surface electromyogram potentials were recorded from the abductor pollicis brevis, abductor digiti minimi, and extensor digitorum brevis muscles in response to finely graded nerve stimuli. Successive potentials were subtracted to obtain intermediate potentials 2%, 5%, 10%, 20%, and 50% of the maximal compound muscle action potential (mCMAP). The average latency of the onset and negative and positive peaks, and the average duration of the negative phase and whole potential were similar for all degrees of fractionation, although smaller fractionation was associated with increasing variability. An initial positivity occurred with some of the smaller fractions of the CMAP, particularly those with the lowest stimulus threshold. Submaximal CMAPs closely resembled the mCMAP once their amplitude was greater than 5–10% of the mCMAP. Our results support the common practice of expressing H‐reflex amplitudes as a percentage of the M wave and may partly explain why reflexes “scale” in response to tonic activation. © 1996 John Wiley & Sons, Inc.