A marker-based measurement procedure for unconstrained wrist and elbow motions

A protocol is proposed to obtain the joint angles of wrist and elbow from t racked triads of surface markers on each limb segment. Cuffs placed on the limb support the rigidity of the triads. Additional markers are used to mar k the approximate positions of joints. Corrections of surface marker data f or skin motion are derived from a priori knowledge about plausible joint mo tions. In addition, ill-conditioned states are trapped when the elbow is ne arly fully extended. The: protocol is applied to sample motions which demon strate the use and the effect of the corrections. The results show that the model assumptions are reasonable and that accurate joint rotations can be obtained. The correction steps prove to be an essential part of upper-extre mity movement analysis. (C) 1999 Elsevier Science Ltd. All rights reserved.