2018 Volume 51 Issue 1 Pages 11-20
In budo and sports, to understand complex movements scientifically, it is necessary to reduce them into simple models and to analyze them on the basis of mechanical laws. As the first step in the theoretical study of movements, Sakai et al. (2016) initiated the study of bar mechanics, which are applicable to various movements in sports. In particular, they focused on the effects of inertial force on human movements. One of the important consequences is the “braking effect”, which explains the phenomena that decelerating one end of a moving bar causes instantaneous acceleration of the other end. In this paper, as an extension of the previous work on the braking effect, we study the multistep braking effect on a single bar. This is motivated by the men-uchi (strike to the head) movement in kendo in which a time difference appears in the extensions of the left and right arms. We find that multistep brakes actually accelerate the end of a bar more efficiently. As the number of braking steps increases, the final velocity of the end point increases, but there is an upper limit. While a single brake increases the final velocity of the end point maximally by 150 percent, and by 162 percent with double brakes, as the number of the braking steps are infinite the final velocity approaches 172 percent of the initial velocity. We also discuss how we can apply these results to men-uchi movements.
