H Ch Scholle | PubMed Health

PubMed2005

Improved evaluation of back muscle SEMG characteristics by modelling.

Surface EMG (SEMG) as non-invasive method is a valuable tool in functional studies of movement co-ordination. The interpolation of the SEMG power (EMG mapping) gives information about intra- and inter-muscular co-ordination. It has been shown that SEMG maps of low back pain patients and healthy subjects differ. The only major drawback to SEMG is that volume conduction of muscle tissue, fat, and skin decreases the spatial and temporal resolution of signals. To improve the interpretation of SEMG signals, we have applied high pass filtering of cross covariance functions, which has proved to be useful in increasing the spatial resolution, to SEMG data of the back region. Experimental data demonstrate that SEMG signals from the back extensors show only rarely signs of action potential propagation. This behaviour, also described in the literature, can be explained by a model assuming short, deep muscle fibres, having bipolar end effects, with overlapping positions parallel to the fibre direction. This condition is fulfilled by the mm. multifidii et rotatores which are part of the m. erector spinae. Although the model is simplistic, the agreement between simulations and experiments is good.

Journal Article↗

PubMed2003

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.

Action Potentials↗