Kinematic and kinetic analysis of sit-to-stand and stair-walking with dynamic robot-assisted body weight unloading.

Body weight unloading (BWU) can be achieved by applying a vertical upwards force to the body centre of mass, which reduces the kinetic requirements of walking, hence it may be useful for supporting bipedal locomotion in persons with severe mobility limitations. However, the applicability of BWU for sit-to-stand and stair-walking tasks has not been well investigated. Thus, the present study aimed to perform kinematic and kinetic analysis of sit-to-stand and stair-walking in young healthy adults using dynamic robot-assisted BWU. Twenty participants performed sit-to-stand and stair-walking at a self-selected speed at 0-50 % BWU. Ground reaction forces (GRFs), sagittal plane ankle, knee, and hip joint angles, and body centre of mass displacement and velocity were obtained using 3D motion capture and a force plate. To compare different BWU conditions, signal trajectories were time-normalised and analysed using Statistical Parametric Mapping (SPM). Signal trajectories were subsequently analysed to separate amplitude and temporal effects. Main effects of BWU were observed for all kinematic and kinetic variables obtained (p < 0.05) during sit-to-stand and stair-walking. Post-hoc analyses revealed progressive reductions in GRFs and concurrent modulations in lower limb joint angles at increasing BWU (p < 0.01). As hypothesised, dynamic robot-assisted BWU yielded reduced kinetic requirements during sit-to-stand and stair-walking in young healthy adults. However, statistical separation of amplitude versus timing effects revealed significant alterations in joint angle trajectories, especially at higher BWU intensities. Regardless, robotic-assisted BWU may facilitate sit-to-stand and stair-walking movements with variable loading-intensities.