In this study, a four-bar linkage with coupler point is designed to guide the arm motion exercise for muscle strength rehabilitation. The hand grasps the coupler point during rotation. The coupler point can generate different shape of trajectories by changing the coupler point’s relative location and the linkage’s dimensions. The rotating coupler point is used to guide the user’s hand to exercise arm muscles for rehabilitation. A two-dimensional (2D) musculoskeletal arm model is used to simulate the arm motion. The inverse-dynamics-based optimization method is used for trajectory reconstruction to determine the joint torque and muscle forces. The effect of different shapes of coupler point trajectory on specific muscle force excise is investigated, such as kidney shape, heart shape, and woven shape trajectories.