Influence of motoneuron firing synchronization on SEMG characteristics in
dependence of electrode position.
Kleine, Bert U., Dick F. Stegeman, Daniela Mund, and Christoph Anders.
1Motor Research Group, Institute of Pathophysiology, Friedrich-Schiller-University,
Jena, Germany; 2Department of Clinical Neurophysiology, Institute of Neurology,
University Medical Centre, Nijmegen, The Netherlands; 3Department of Neurology,
University of Tübingen, D-72076 Tübingen, Germany
APStracts 8:0339A, 2001.
The frequency content of the surface electromyography (SEMG) signal, expressed as
median frequency (MF), is often assumed to reflect the decline of muscle fiber
conduction velocity in fatigue. MF also decreases when motor unit firings synchronize,
and we hypothesized that this effect can explain the electrode-dependent pattern in our
previous recordings from the trapezius muscle. An existing motoneuron (MN) model
describes the afterhyperpolarization following a spike as an exponential function on
which membrane noise is superimposed. Splitting the noise into a common and an
individual component extended the model to a MN pool with a tunable level of firing
synchrony. An analytical volume conduction model was used to generate motor unit
action potentials to simulate SEMG. A realistic level of synchrony decreased the MF of
the simulated bipolar SEMG by ~30% midway between endplate position and tendon but
not above the endplate. This is in accordance with experimental data from the biceps
brachii muscle. It was concluded that the pattern of decrease of MF during sustained
contractions indeed reflects MN synchronization.
Received 26 December 2000; accepted in final form 29 May 2001
APS Manuscript Number A1237-0.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 29 June 2001