Biomechanical assessment of sitting pivot transfer tasks using a newly developed instrumented transfer system among long-term wheelchair users

This paper describes the technical characteristics of a transfer assessment system, along with details on three-dimensional (3D) upper extremity (U/E) kinematics required to compute U/E joint forces and moments using inverse dynamics during a displacement of the body in a sitting position from an initial surface to a target one (sitting pivot transfer (SPT)). This system includes five instrumented surfaces designed to measure position (center of pressure (COP)), magnitude and direction of the tri-axial force components underneath the feet, hands (leading and trailing) and buttocks (initial and target seats) during SPTs. Linearity, COP position and natural frequency tests were performed to confirm the accuracy of the transfer assessment system outcomes. Preliminary data of one person with spinal cord injury performing SPTs toward a target seat of same height (50 cm) and additional ones toward a raised target seat (60 cm) are presented. The transfer assessment system was found to be safe, versatile in terms of height- and width-adjustment ranges, portable within a laboratory environment, easy for experienced rehabilitation scientists to use, and allowed for valid quantification of reaction forces during SPTs as confirmed by the overall accuracy test results. Combined with the 3D U/E kinematic and anthropometric parameters, the transfer assessment system outcomes allowed for the quantification of U/E joint forces and moments. Preliminary results highlight the kinematic and kinetic specificities of the leading and trailing shoulders and elbows during SPTs. The impact of modifying target seat heights on the kinematic and kinetic outcomes during SPTs is explored. The transfer assessment framework proposed is useful for research and offers a wide spectrum of possibilities for acquiring new biomechanical knowledge on SPTs that may strengthen clinical practice guidelines, targeting the preservation of U/E integrity following SCI.