Correlation between leg muscle movement and electrodes motion artifact during whole body vibration

Vibration treatment by oscillating platforms is more and more employed in the fields of exercise physiology and bone research. The rationale of this treatment is based on the neuromuscular system response elicited by vibration loads [1,6]. Surface Electromyography (EMG) is largely utilized to assess muscular response elicited by vibrations and Root Mean Square (RMS) of the electromyography signals is often used as a concise quantitative index of muscle activity; in general, EMG envelope or RMS is expected to increase during vibration [1]. However, it is well known that during surface bio-potential recording, motion artifacts may arise from relative motion between electrodes and skin and between skin layers. Also the only skin stretch, modifying the internal charge distribution, results in a variation of electrode potential [2,4]. The aim of this study is to highlight the movements of muscles, and the succeeding relevance of motion artifacts on electrodes, in subjects undergoing vibration treatments. EMGs from quadriceps of fifteen subjects were recorded during vibration at different frequencies (15-40 Hz); Triaxial accelerometers were placed onto quadriceps, as close as possible to electrodes, to monitor motion. The muscle displacements showed a peculiar behaviour reflecting the mechanical properties of the structures involved. Motion artifact related to the impressed vibration have been recognized and related to movement of the soft tissues. Signals spectra also revealed sharp peaks corresponding to vibration frequency and its superior harmonics, in accordance with accelerometers data. The knowledge of skin motion could help in a better description of motion artifact origin and in filter-out motion-related electrode signals.