External pressure at the hand during object handling and work with tools

Abstract

Hand size, pressure-pain threshold (PPT) and hand strength were measured on 15 subjects. External pressure on the hand was measured, using small capacitive pressure sensors, while grasping cylinders (Ø 10–100 mm) and handling tools. Subjective ratings of cylinder preference, pressure, discomfort and pain were recorded. PPT measured with six years interval differed significantly; however, the PPT was stable over shorter periods. For grasp tasks, the results indicate that hand size is critical when the external force requirement is constant, while there is an interaction between hand size and strength when it varies. When gripping a cylindrical object, the fingers were exposed to the largest pressure. The gripping action was dependent on cylinder diameter, and the subjects strongly preferred cylinders with 30–40 mm diameter. The average pressure during tool handling was 250 kPa or less, except for high-force tools (plate shears). In general, the fingers registered high external pressure and the carpal canal tunnel low pressures. The pain threshold was exceeded during short periods during work with tools. Subjective ratings of pressure and discomfort were significantly correlated with external pressure, but not significantly with pain.