A simple device for kinematic measurements of human movement

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Abstract
A simple device for three-dimensional recording of human movement was developed. It consisted of four rigid bars linked together by three joints. At each joint an optical transducer, connected to a PC computer via an electronic interface, measured the joint angle, rendering it possible to compute the displacement of one end (measuring end) relative to the other (reference end). This kinematic arm was validated (i) in static conditions; (ii) in dynamic conditions; and (iii) during human jumping. The measured error was 0·4%±0·5% (mean±s.d.) on distance measurements in static conditions, 0·l%± 1·6% on 0·57 m.s−1 rotation velocity measurements and 3·2% ±3·3% on 3·56 m.s−2 rotation acceleration measurements, and l·6%±20·7% on force measurements during human jumping. These error values are equivalent to or lower than errors linked to tracking systems or to film or video analysis. Therefore, if the movement is not disturbed by the spatial limitation due to the mechanical link with the measuring end, the kinematic arm provides a simple and fast tool to study three-dimensional human movements.