Hand-handle orientation and maximum force

Many industries today have very high incidence rates for cumulative trauma disorders (CTD). Several factors are known to contribute to the onset of CTDs including the application of high forces. A reasonable inference is that a tool and/or task design that requires less grasp muscle effort will less likely to contribute to CTD. The findings of a study by Jorgensen et al. (1989) indicated that the direction of power grasp force relative to the hand appears have a significant effect on the magnitude of the force exerted. This study was conducted to confirm and quantify these force magnitude differences for four orientations of opposition forces to the hand in a power grasp for two friction conditions and two handle shapes. The results showed that the orientations can be placed in two groups, one containing a single orientation and the other grouping containing the remaining three orientations. The orientation found to be superior to the other three was the pull resisting a force at the bottom of the hand (nearest digit 5). In this orientation, the hand is better able to oppose forces acting at the hand-handle interface than in two of the other orientations. The results of this research indicate that avoidance of the inferior orientations (those acting to ulnarly deviate the wrist) will be beneficial. Because current jobs are designed without considering the force direction, workers are exposed to unnecessary stresses. This study will give work task designers one more piece of information to help reduce the stresses on the hand and wrist.