Formulation of the Degree of Postural Instability Based on the COP and EMG Data

The purpose of this study is to formulate the degree of postural instability in working based on the data acquisition of center of pressure (COP) and surface electromyography (EMG). In the previous studies [1]-[4], the limits to which we could move the COP such as the functional stability limits and the balance limits were obtained. In this study experiments were carried out for ten male subjects to measure the COP displacements and EMG signals of leg muscles when the subjects leaned as far as possible while taking every four brief pauses in four directions. As a result, it was found that the muscle load increased exponentially with the COP displacement. Therefore we considered that postural instability also increased exponentially with the COP displacement. Finally we formulated the degree of postural instability. By installing the formulation into a digital human model Jack (Siemens), proactive evaluation of working postural stability could be conducted.