An elbow joint boost device has first and second frames to be attached to the forearm and lower arm of a patient. A guide mounted on the first frame extends generally along the respective one of the forearm and upper arm. A link is mounted on the guide for sliding movement along the guide, and a spring acts in tension between the sliding link and a point on the second frame remote from the patient's elbow. As the patient straightens and bends the elbow, the link can slide along the guide, varying the leverage of the tension spring.
