Investigation of Grip Force, Normal Force, Contact Area, Hand Size, and Handle Size for Cylindrical Handles

Objective: To investigate relationships among grip forces, normal forces, contact area for cylindrical handles, handle diameter, hand size, and volar hand area. Background: Data describing those relationships are needed to predict thrust forces and torque capability. Method: Additional analyses were performed retrospectively on data collected in two previous studies in which participants performed maximum grip exertions on cylinders (diameter 38-83 mm) while grip force, normal force, and contact area were recorded. The length, width, and volar area of the hand were measured. Results: Average total normal force on cylinders was 2.3 times greater than grip force measured using a split cylinder (R(2)=65%), regardless of the handle diameter examined. The ratio of handle diameter to hand length explained 62%, 57%, and 71% of the variances in grip force, normal force, and contact area, respectively. Estimated hand area (hand length x width) had a linear relationship with measured hand area (using photographs; R(2)=91%), although it was 8% less than the measured area. Conclusion: This work describes the relationship between normal force and grip force independent of handle size (for handle diameters from 38 to 83 mm). Normal force and contact area can be explained by the interaction between handle size and hand size. Hand area can be estimated by hand length times width. Application: The quantitative relationships described in this paper can be used in the design of objects and hand tools to determine optimal handle sizes for maximizing grip force, total normal force, or contact area.