Development of upper limb orthosis with shoulder joint tracking system

This study describes the use of a novel orthosis in individuals with restricted upper limb movement owing to decreased muscular strength. In such individuals, it would be effective to neutralize the influence of gravity so that they can freely move and hold their arms. Hence, we developed a novel orthosis that compensates for each joint moment. An auxiliary method of the orthosis involves weight compensation mechanisms that constitute only a spring, wire, and pulley, because assisting methods that involve electricity are disliked by users. Our novel orthosis has two advantages compared with the conventional orthoses: (1) it allows the use of the subject's arms in a wide range of motion and (2) external forces do not hinder upper limb motion because the auxiliary function make the upper limbs feel lighter. Therefore, there is negligible discomfort and skin irritation with the long-term use of this orthosis. We evaluated the effect of assisting muscular strength by applying our orthosis in healthy male subjects. Surface electromyogram measurements in the deltoid and trapezius muscles revealed remarkable reduction of muscular activity, which is necessary for improvement in upper limb motion. In conclusion, the novel orthosis enabled stress-free upper limb motion by means of a weight compensation mechanism.