Considering Task Force Requirements for Hand Posture Predictions

Abstract

This work is concerned with how finger, wrist, elbow and shoulder postures are affected depending the orientation and magnitude of hand force exerted. Six participants, 3 females and 3 males from the ages of 18-25, where asked to perform three exertions (100%, 30% and 10% MVC) perpendicular to an aluminum plate in 45°, 0°, 45° and 90° pitch at elbow height. Exertions were performed using the whole hand and the fingertips. We recorded inter-digit joint angles as force is applied to compute joint moments, and hand and finger motions so that they can be modeled and mapped for each condition. Results show that posture changes depending the force exerted and the threshold for significant changes is at force levels below 50%MVC. Comparing exertions over 50%MVC with exertions of 50%MVC or lower, elbow and wrist angles were significantly greater, and forearm was more perpendicular to the surface. Distance between hand and shoulder increases by decreasing the required %MVC. At 0° pitch males exerted all the required forces using shoulder abduction. Awkward postures, such as shoulder abduction, are some of the contributing factors to develop upper extremity musculoskeletal disorders and must be taken into account while designing tasks.