Reliability of measuring human segment three-dimensional orientation using wearable sensor system

A new method for analyzing human segment three-dimensional orientation is presented. A wearable sensor system based on triaxial accelerometers alone was developed, and later was tested on a thigh to calculate the pitch and yaw angles of the thigh with the accelerations captured by the system. Wearing the developed system, eight volunteer subjects walked in the work space of a high-accuracy camera system at three self-selected slow, normal and fast walking speeds. Calculated pitch and yaw angles of the thigh in the local frame were compared with those measured from high accuracy camera system. The mean differences (e_mean) of the calculated angles range from 0.4478° to 1.1351° in the Yr direction and from 0.5667° to 0.8973° in the Xr direction at three different speeds. The correlation coefficients (R) were above 0.8113 in the Yr direction and above 0.9031 in the Xr direction across all conditions. The result shows that the wearable sensor system gives a reasonably accurate measurement of the pitch and yaw angles of the lower limb segment. Therefore, the original method using only one kind of sensor (accelerometer), since it´s accurate, inexpensive and simple, is suitable for the evaluation of human segmental orientation, for the purpose of assessing spatio-temporal gait parameters and monitoring the gait function of patients.