METHODOLOGICAL LIMITATIONS OF EMG-BASED BIO-MECHANICAL MOTION ANALYSIS

The purpose of the present study was to investigate the influence of different methods on the identification of the onset of EMG and force. Using the example of electromechanical delay (EMD), results show a rather distinct dependence of onset times of both EMG and force on the applied method and within the threshold values. However, no automatic method has been found for providing reliable and comparable results. For determination of time sensitive values such as EMD, the visual method seems to be the only advisable method regarding accuracy and reliability. This method provides the earliest onset times, lowest threshold levels and a muscle independent course of EMD related to initial muscle length. For other cases of motion analysis or motor research, with some provision for acceptable inaccuracies of about ±20-30ms, this study illustrates why the preferable method should use a moderate low-pass filter and low percentage thresholds. KEY WORDS: methods, electromechanical delay, EMG-onset, force-onset INTRODUCTION: Electromyography and dynamography are the only basic methods used in biomechanical motion analysis, providing information about non-visible activities and forces. E.g. lifting a leg from a horizontal position requires a force generation greater than th