Deviation Analysis of Upper Leg Angle Measurements: Insights into Inertial Sensor Placement Strategies

In order to preserve the health of workers, extensive ergonomic analyzes of the load on the human body are carried out, but in order to obtain concrete results and the possibility of better optimization of the work task, it is necessary to have reliable data that represent actual measured values. This paper provides an insight into the deviations of upper leg angle measurements depending on the placement position of the inertial sensors and offers guidelines on how to minimize measurement deviations. In this study, the values of the root square mean (RSM) deviation of the angles that occur when measuring with inertial sensors are presented. Comparison with previous studies showed that the deviations without improvement techniques are similar to the previously obtained results. Also, the possibility of a non/conventional way of attaching the sensor to the examinee's leg was examined and compared with previously obtained results. The improved measurement method resulted in angles whose average RMS was reduced by almost 78%.The values of RMS of improved method are 1.3° for hip flexion and extension and 0.57° for hip adduction and abduction, which brings inertial sensors to the level of accuracy and precision of other much more expensive and complex methods of recording angles of the human upper leg.