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Examination of the myoelectric activity of back muscles during random vibration--methodical approach and first
1Department of Occupational Health, Federal Institute for Occupational Safety and Health, Group AM 4.3, Biological Effects of Vibration and Noise Nöldnerstr. 40-42 D-10317, Berlin, Germany.
Objective:
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.
Design:
A procedure involving wavelets and digital filtering has been used for the removal of artefacts from the electromyogram during whole-body vibration.
Background:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
Relevance:
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.