Experiments on wrist deviation in manual materials handling

One potential hazard in manual materials-handling (MMH) jobs is the wrist deviation required whena container is moved.Container handles may help control this deviation, but if container handles are to be designed to fit the operator, an evaluation of the effect of wrist deviation on MMH tasks is required. After a pilot experiment, a one-handed holding task was used to imposefive wrist deviations on the subject, ranging in equal steps from 20° ulnar to 200 radial. Two weights of container (9 and 13kg) were tested. Measurements of heart rate, psychophysical variables and angles of the hand and arm were taken on 15 male and 15 female subjects.No significantgender effects werefound but changes in imposed deviation wereequivalent to a 16% change in box weight. Radial deviation proved worsethan ulnar deviation. The hand and arm accommodated to the imposed deviation by deviating the wrist but mainly by allowing the box handle to slip within the hand.