On the Design of an Assistive Knee Exoskeleton for Flutter Kick of Diving

During the flutter kick of diving, the thigh exerts force to drive the calf, then the calf drives the fins, and two legs alternately kick downward to provide propulsion. According to the biomechanics of lower limbs, the knee joint is prone to flexion during the process of pressing and kicking due to the force of the hip joint and the water resistance of the fins, which quickly leads to a decrease in propulsion. Divers often need a lot of muscle activation to maintain the knee joint extension. To reduce the activation and fatigue of the quadriceps femoris of the diver during kicking, this paper proposed an assistive knee exoskeleton based on an elastic structure of cam and flat leaf spring. During the downward stroke of the kicking, the cam raises the leaf spring during the knee flexion. The leaf spring stores elastic potential energy during deformation, thereby generating an extension moment to prevent further flexion of the knee. During the upward stroke of the kicking, the elastic potential energy stored in the leaf spring is released, assisting the extension of the knee. In this paper, we complete the parameter design of the rotation stiffness, cam, and flat leaf spring, as well as a prototype implementation. A platform experiment is to verify the tread between the generated torque and the theoretical design. Underwater diving experiments on two subjects were carried out under the conditions of wearing and not wearing the exoskeleton. The results show that the activation of the vastus medialis significantly decreased under the exoskeleton assistance.