The influence of wrist and forearm position, handle diameter, and grip exertion on palmar hand force distribution

Includes bibliographical references (pages [120]-124).In order to reduce the risk of occupational cumulative trauma disorders of the upper extremity, it is important to understand the factors that have been linked to the incidence of such disorders. This study focuses on quantifying the effects of forearm position (pronated and semipronated), wrist position (30 flexion, neutral, and 30 extension), handle diameter (1.0,1.5, 2.0, and 2.5 inches), and submaximal exertion level (25%, 50%, and 75% of maximum voluntary contraction). A full factorial design was used to analyze the palmar force distribution and electromyographic activity of the forearm flexor muscles that resulted from combinations of these factors. Force data was analyzed for nine force-sensing resistors (FSRs) that were placed on the phalanges and metacarpophalangeal joints of ten subjects during isometric power grip on cylindrical handles. The muscular efficiency of the forearm flexor muscles was also evaluated by calculating the force-to-EMG ratio. The results indicated that the force distribution was significantly affected by all factors. Average EMG activity was significantly affected by all factors except wrist position. In terms of force generation and muscular efficiency, and for the factors studied, the optimal conditions for forceful tasks involving a power grip on cylindrical handles were determined to consist of: 1) a semipronated forearm position, 2) a wrist angle between neutral and 30 extension, and 3) a handle diameter of 1.5 inches. The 50% MVC exertion level was found to exhibit the best muscular efficiency among the exertion levels tested. In order to reduce between-subject variability, anthropometric grip diameter was successfully used as a blocking factor for the EMG activity data. However, blocking by grip diameter did not significantly improve the force distribution results.M.S. (Master of Science