Parallel cross-correlators for investigating reliability of measurement of muscle fiber conduction velocity using surface EMG

Muscle fibre conduction velocity may be measured by cross-correlating two surface EMG signals detected at two different locations along the muscle fibres. However, it has been reported before that the velocity measured using this technique is dependent on the location of the electrodes on the skin surface of the muscle. Relatively high variations in the measured velocity are experienced when the electrodes are only slightly displaced from their positions. In this paper, eight parallel on-line polarity correlators, and an electrode array which permits various configurations of electrode geometry and spacing are used to investigate these variations. By carrying out simultaneous measurements from a number of successive locations along the path of propagation of action potential, the way the conduction velocity may vary along the muscle fibres is investigated. The variations of the measured velocity with time, as well as its dependence on the electrodes geometry and their location on the muscle are also investigated. The results obtained seem to suggest that the conduction velocity might not be uniform along the entire length of muscle fibres