Functional handgrip test to determine the coefficient of static friction at the hand/handle interface.

The aim was to devise a method of measuring friction at the hand/handle interface during a functional handgrip task. No descriptions of methods of this kind was found in the literature. An indirect technique of measuring normal grip force was employed to determine friction at the hand/handle interface while performing a functional handgrip action with a grabrail. The coefficient of static friction was calculated between palmar skin (dry, wet, and soapy hands) and five grabrail materials (stainless steel, powder-coated steel, chrome, textured aluminium and knurled steel). Thirty subjects participated (15 female, 15 male), who were aged from 17 to 45 years with a mean age of 30 years. Knurled steel produced a significantly larger mean coefficient of static friction than chrome, powder-coated steel and stainless steel, and textured aluminium had a significantly larger coefficient of static friction than stainless steel. Soapy hands produced the lowest mean coefficients (0.46+/-0.04), significantly less then dry (1.72+/-0.16, p <0.001) and wet hands (1.42+/-0.16, p <0.001). This study has demonstrated the influence of grabrail material and palmar skin treatments on static friction at the hand/handle interface. The use of a functional test that incorporates an indirect determination of normal handgrip force has provided a quantitative method of observing stability at the hand/handle interface.

Static friction properties between human palmar skin and five grabrail materials.

The purpose of this study was to investigate the static friction properties between human palmar skin and five grabrail materials (chrome, stainless steel, power-coated steel, textured aluminium and knurled steel) for dry, wet and soapy hands. Thirty subjects (15 female, 15 male) participated in this study, their ages ranging from 19 to 45 years with a mean age of 28 years. The normal force, friction force, and coefficient of static friction were determined by measuring three-dimensional forces while slipping the palm of the hand over the surface of a grabrail. A repeated measures ANOVA indicated that gender, age, hand size and trial effect had no significant influence (p>0.05) on these results. The coefficient of friction (p<0.001) and friction force (p<0.001) were significantly lower when the hand was soapy than when it was dry or wet. The normal force applied when the hand was soapy was significantly greater (p<0.001) than when it was dry or wet. No significant difference was found between dry and wet hands. The two textured materials displayed superior friction properties when the hand was soapy, while the smooth materials performed best when the hand was dry.