It was frequently observed that participants grasped the tip of the handles when clamping with the upsidedown gripping method. This grasping position increased the length of lever arm so that handle-squeezing forces in the starting phase were larger with the upside-down gripping method than with the pistol gripping method, especially at elbow and shoulder heights. However, this behavior was not found during the clamping phase and was not significant for clamping forces because participants controlled both handle-squeezing and clamping forces to reach a force level where they felt the wooden block was gripped tightly enough during the clamping phase regardless of gripping method.
Males produced larger clamping and handle-squeezing forces than females. Females exerted about 52 % clamping force of males in the ending phase and about 66% handle-squeezing force in the clamping phase. These findings more expected due to physiological and biomechanical difference between genders (Hallbeck and McMullin, 1993; Zellers and Hallbeck, 1995).
In conclusion, a bar clamp handle was redesigned and the redesigned clamp compared to the original clamp in this study. When using the redesigned clamp, objects could be clamped more tightly and also this redesigned clamp had better efficiency with less forearm fatigue. Based on these results, guidelines for the use of this type of clamp can be suggested. It should be used with both hands at or below the elbow height of operators, using the pistol gripping method. Through this study, it was shown that the application of ergonomic guidelines for handtool design could increase tool efficiency and usability.