Assisted Spatial Sit-to-Stand Prediction-Part 1: Virtual Healthy Elderly Individuals

Sit-to-stand (STS) motion is a key determinant of functional independence for the senior people. This paper extends a predictive dynamics formulation previously reported to predict the assisted STS motion, i.e., the motion with a mechanical assistance, unilateral grab-rail bar which is placed on the right side of the virtual-individuals with a vertical orientation. The formulation is able to predict kinetics and kinematics not only in the sagittal plane, but also in frontal and transverse planes. Two different objective functions are tested: The first one is the dynamic effort and the second one is the dynamic effort plus the difference between right and left side support reaction forces (SRFs). Results show that sagittal plane kinematics and kinetics are not affected by the introduction of the grab-rail bar, whereas some significant differences are seen in the medial/lateral and anterior/posterior components of kinematics and kinetics. The healthy elderly group places a priority to the stability during an assisted STS task. The placement of the grab-rail bar on the right side results in a significant decrease in the left knee joint torque. Results in this study are consistent with those reported from the literature.