A novel mechanism to support the sit-to-stand and squat-to-stand physical training for rehabilitation purposes

Abstract

In patients with neurological impairment, muscles become stiff, and the joint range of motion (ROM) is restricted. Physical rehabilitation training is required if they cannot perform tasks like sit-to-stand motion. The existing devices support the trunk with limited degrees of freedom (DOF) and fixed shank pad support that arrests ankle, knee, and hip joint ROM and its associated muscle activations. The manual transfer increases falls and the risk of lower back injury. This study proposes a mechanism that supports the shank and trunk by moving assistance in joint ROM. Natural sit-to-stand (STS) and squat-to-stand motion experiments were conducted in the motion capture system with twenty healthy participants. For Inverse kinematic and motion event/phases analysis, Visual 3D biomechanics software was used. From inverse kinematics, trunk & shank angle, velocity, and hip joint position were calculated. A 3-DOF mechanism design consisting of 13 links and 17 joints is proposed based on the inverse kinematics analysis of squat-to-stand movements that accommodate the STS joint ROM. A CAD model of the mechanism is created and imported into Simscape Multibody Dynamic (MATLAB 2023b) software for simulation. Simulated angular velocity and displacement of the trunk and shank compared with experimental data. The proposed mechanism facilitates physical rehabilitation training and reduces the physical burden on caregivers, nurses, and physiotherapists. The 3-DOF assisting trunk support provides coordination with the lower limb to follow the natural path. It includes toileting facility transfer due to its motion up to squat position. Safe transfer from hospital beds to wheelchairs. © The Author(s) 2025.