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The "classical" body-powered above elbow arm prosthesis continues to be used by a large majority of arm prosthesis users, even though many more modern devices are available. The authors present a set of experiments designed to compare performance of unimpaired arms and body-powered prostheses of 6 unilateral amputees. The experiments were designed to measure qualitatively how well the body-powered prosthesis can be used to perform free-motion tasks, as well as to study the qualitative features of movement common to both the prosthesis and unimpaired arm. It was found that regular peaks in velocity were common to both the unimpaired arm and prosthesis movements, suggesting that movements were composed of a sequence of successive actions. In addition, it was found that the body-powered prosthesis generally required more movements than the unimpaired arm to meet an accuracy constraint and could not keep up with the unimpaired arm when a speed constraint was imposed, even though the body-powered prosthesis was able to match the unimpaired arm in a simple nondynamic task.