Effect of friction and load on pinch force in a hand transfer task

The effect of friction and load on pinch force was studied in a simple hand transfer task using a repeated measures design and ten men. Subjects moved a container between two targets, 450 mm apart, at a slow, self-paced speed. The levels of mass in the container were set at 0.8, 2.5 and 4.2 kg (7.5, 24.5 and 41.5 N respectively). The handle materials were sandpaper and smooth aluminum. Applied pinch force was measured via a strain gauge mounted in a specially-designed handle attached to the container. Dependent variables were peak and 'steady-state' pinch force. The main and interaction effects of load and friction were significant. The friction effect was significant only for the highest load which, on average, elicited peak pinch forces of 16-70% of maximum voluntary force. This suggests that these men were not sensitive to friction effects at the lower loads. Results suggest that the use of tool handle friction enhancements may reduce required pinch forces for objects requiring upwards of 50% or more of maximum pinch strength.