Design of an exoskeleton for strengthening the upper limb muscle for overextension injury prevention

Several methods have been proposed for upper limb muscle training using exercise devices or machines to strengthen the muscle groups. However, most exercises control the direction of resistance to isolate specific muscle groups that need to be trained. A compact and cost-effective upper limb exoskeleton design with a 3-DOF shoulder joint and a 1-DOF elbow joint allows a patient or a healthy individual to move the limb in different planes and increases resistance through adjustments of the spring length to train more muscle groups. The exoskeleton springs were designed to equalize the joint torques for the shoulder and elbow joints with the joint torques obtained from free-weight exercises. Experimental data of the joint torques for two healthy subjects for shoulder abduction–adduction, flexion–extension, and elbow flexion–extension exercises with the exoskeleton were compared to measurements obtained from the upper limb dumbbell lateral raise, the dumbbell frontal raise, and the dumbbell curl exercises. The results of our preliminary evaluation showed that this design had an equivalent effect on the joint torques of shoulder and elbow to the free-weight exercises without the risk of overextension injury. Ultimately, this study provided a design and prototype for an upper limb exoskeleton.

► We model an upper limb exoskeleton: 3-DOF shoulder joint and 1-DOF elbow joint.
► Motivation was a concern of overextension presented in free-weight exercise.
► Linear relationship in the external load and the loaded spring was determined.
► Design parameters of the exoskeleton for average-sized human beings were provided.
► Comparisons were made from the actual-measured data from the prototype evaluation.