Selective spatial information from surface EMG after temporal filtering: the application to interference EMG using cross-covariance analysis.
OBJECTIVE
An increased spatial resolution in multichannel surface EMG recordings would provide new possibilities for the investigation of intermuscular and intramuscular coordination. A known analytical solution for volume conduction allows the conclusion that a high pass filtered surface electromyography (SEMG) signal contains information from a smaller environment near the recording electrode and therefore provides a higher spatial resolution.


METHODS
The present paper concerns experiments on 9 subjects to measure, from the human biceps brachii muscle during static isometric contraction, using multichannel surface EMG. Cross-correlation functions between bipolar SEMG channels were calculated and high pass filtered.


RESULTS
The correlation peaks showed the signs of propagating action potentials. The spatial width in the direction perpendicular to the muscle fibres decreased with increasing cut-off frequency. There exists an optimal cut-off frequency, which provides the best spatial resolution. It correlates with the thickness of the subcutaneous fat layer which causes a minimum depth of the active muscle fibres measured.


CONCLUSIONS
High pass filtered cross-covariance functions of bipolar SEMG channels have an increased spatial resolution perpendicular to the muscle fibre direction and the frequency content of the signals can potentially give an indication of the depth of the active muscle fibres.
Grassme
R
R
Motor Research Group, Institute of Pathophysiology, Friedrich-Schiller-University Jena, Erfurter Strasse 35, D-07740 Jena, Germany. rgra@moto.uni-jena.de
Stegeman
D F
DF
Drost
G
G
Schumann
N P
NP
Scholle
H Ch
HCh
D000200:Action Potentials; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008959:Models, Neurological; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology*