[show abstract][hide abstract] ABSTRACT: 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.
[show abstract][hide abstract] ABSTRACT: 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.
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.
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.
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.
[show abstract][hide abstract] ABSTRACT: The study aims at a precise characterisation of intramuscularly varying recruitment patterns within the triceps brachii muscle (long and lateral head; proximal, medial, distal regions) in the time course of averaged step cycles during locomotion.
The triceps brachii muscle of 15 Hannover rats was investigated with a supramuscular 16-electrodes grid during treadmill locomotion. Multi-channel electromyogram (EMG) was recorded simultaneously with high-speed videography. The rectified and smoothed EMG was time-normalised. EMG profiles and dynamic EMG-map series were calculated. Differences between EMG distribution patterns were tested by multivariate analysis of variance.
In the pre-stance phase EMG activity increased especially in the proximal long head. It most likely propagated from lower muscle layers of the long head. During stance phase the EMG activity of the lateral head rose steeply and exceeded those of the long head in short time. The fastest steps show the highest EMG amplitudes.
EMG registrations with grid electrodes help in the identification of intramuscular co-ordination processes during locomotion. While the EMG profiles characterise the time course, the topographical distribution is better represented in dynamic EMG interference maps. The dynamic changing activation patterns of triceps brachii depend on the phase of the step cycle. This clearly indicates the different functions of the muscle heads.
[show abstract][hide abstract] ABSTRACT: Multichannel surface EMG recordings of a multiheaded skeletal muscle during cyclic locomotion combined with cineradiography
were analysed in a chronic experiment. The resulting detailed two-dimensional activation pattern from the long and lateral
triceps brachii heads of the rat during treadmill locomotion were combined with gait characteristics and fibre typing of the
muscle. Shortly before ground contact of the forelimb, maximum muscle activity was found in the proximal part of the long
head of the muscle. During the stance phase maximum activity was observed in the proximal part of the lateral head. The frequency
dependent behaviour of cross-covariance functions over both muscle heads confirmed this selective shift in activation. In
the lateral triceps brachii head of the investigated rats, exclusively type II fibres were found. In the long head the frequency
of type I fibres was the highest in the deep muscle layers, proximally more than distally, whereas type II fibres were dominant
in more superficial muscle layers. A combination of physiological and histological findings supports an anticipating mechanism
whereby fine-tuning of the vertical foot down manoeuvre is mainly achieved by the (type I fibre dominated) proximal deep compartment
of the biarticular long triceps brachii head and force generation is predominantly executed by the monoarticular lateral triceps
Experimental Brain Research 04/2001; 138(1):26-36. · 2.22 Impact Factor