Effect of Task Direction on the Maximal Pushing, Pulling, Twisting, and Grip Forces

Abstract

Objectiv e:The aims of this study are to understand the effects of task (pushing, pulling, and clockwise and counter clockwise twisting) direction on the maximal output and their grip forces and to explore the relationship between the maximal output and the grip forces.Background: Knowing the normative maximal grip force is not enough to design a good hand tool. The industrial designers should understand the required grip forces in various motions toward a specific direction to make an effective and efficient hand tool. Method:Eighteen healthy volunteers participated in the series of isometric maximal output force tests. A custom-made force measuring equipment collected the output and the grip forces for three seconds. Force measurements along the vertical, coronal and sagittal axes were randomly repeated three times. Results:The pulling was strongest and the pushing was weakest in all directions. The effect of motion on the output forces varied in different directions. The corresponding grip force increased in the order of pushing, pulling, clockwise twisting, and counter clockwise twisting in all directions. The maximal output and their grip forces were highly correlated but the relationship was affected by motion and direction. The regression coefficient was greatest in pulling and smallest in clockwise twisting. Conclusion:The effect of motion on the output forces varied in different directions. The maximal output and their grip forces were correlated but the relationship was affected by motion and direction.Application: Findings of this study can be valuable information for industrial designers to develop more productive hand tools and work stations to help preventing the musculoskeletal disorders at work.