Effect of Internal Forces of Human Hand on Rotational Stiffness of Handle

This study aims at clarifying the effects of internal force between human arms and a handle on the handle's rotational stiffness. Rotational stiffness of a handle is determined by internal force stiffness and stiffness of human arms. We use the two-link model to analyze the rotational stiffness due to the internal forces, and measure the rotational stiffness as a function of the internal force. Through theoretical calculation and experimental results, it is reveraled that the stiffness due to internal force is significantiy large in comparison with the stiffness due to the muscle conrtaction of arms. Moreover, it is clarified that one can effectively increase the rotational stiffness of handle by internal force if the handle is pulled.