Selective spatial information from surface EMG after temporal filtering: the application to interference EMG using cross-covariance analysis

• Published in: Clinical neurophysiology Vol. 114; no. 12; pp. 2338 - 2346
• Main Authors: Grassme, R., Stegeman, D.F., Drost, G., Schumann, N.P., Scholle, H.Ch
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 01-12-2003; Elsevier Science
• Subjects: Action Potentials; Biological and medical sciences; Cross-correlation; Electromyography - methods; Female; Fundamental and applied biological sciences. Psychology; Humans; Male; Models, Neurological; Muscle, Skeletal - innervation; Muscle, Skeletal - physiology; Selective muscle activation; Striated muscle. Tendons; Surface EMG; Vertebrates: osteoarticular system, musculoskeletal system; Cross-correlation; Selective muscle activation; Surface EMG; Human; Multichannel recording; Filtering; Coordination; Interference; Electrophysiology; Isometric muscular contraction; Surface electromyography; Striated muscle; High pass filter; Covariance; Biceps brachii muscle; Cross correlation; Spatial resolution
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/S1388-2457(03)00261-X

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.