Examination of the myoelectric activity of back muscles during random vibration--methodical approach and first results.

Abstract

To elaborate methods for an elimination of artefacts and the analysis of the relationship between random whole-body vibration and electromyographic responses of back muscles. A procedure involving wavelets and digital filtering has been used for the removal of artefacts from the electromyogram during whole-body vibration. Back muscle forces contribute essentially to the whole-body vibration-induced spinal load. The electromyogram can help to estimate these forces during whole-body vibration. 38 subjects were exposed to identical random low-frequency whole-body vibration. Artefacts caused by the electrocardiogram in the electromyogram were identified by appropriate wavelets and eliminated in the time-domain. After averaging the individual high-pass filtered and rectified undistorted electromyograms across subjects, the transfer function from seat acceleration to the average electromyogram was determined and used for the prediction of the electromyogram. A sufficient procedure involving wavelets and digital filtering has been elaborated for the removal of artefacts from the electromyogram of back muscles during whole-body vibration. A systematic relationship between random vibration and back muscle-response was obtained and described. The transfer function suggests two different reflex-mechanisms - one elicited below, the other above 4 Hz. The approach of analysing and predicting the muscle-response to random vibration by using the transfer function seems to be promising and could be a valuable tool for the future calculation of muscle forces as an input to active models. The knowledge of the extent and timing of the back muscle-response to random whole-body vibration is relevant for an improved evaluation of whole-body vibration with respect to health.