Yes, from the title I have also expected a much more complete explanation about how to hit for a successful tameshi-wari (test of breaking). In the martial art

Yes, from the title I have also expected a much more complete explanation about how to hit for a successful tameshi-wari (test of breaking). In the martial arts there are 5 or 6 traditional rules for how to hit for a maximum effect, and all of them can be explained by modern physics. The most important 3 are the following. To achieve maximum acceleration, you need maximum force. For maximum force, you need as many muscles as possible to participate in striking. The most powerful muscles are those of the legs, so they must also participate when hitting with the hand, by rotating the hips, whose movement must be transmitted through the abdomen and thorax until the hitting hand. To achieve maximum final velocity of the hand, the hitting arm must not move like a rigid stick, but like a flexible whip (more accurately like an articulated flail), with a wave propagating along it so that the extremity will achieve a maximum speed, much higher than the speed of the extremity of an arm-length stick that would rotate around the shoulder. For this, all the muscles that do not contribute to the acceleration of the hand must be as relaxed as possible. To achieve a maximum transfer of energy into the hitting target, it is necessary for the body part used for hitting to have a maximum equivalent mass. For maximum equivalent mass, the ideal is for the entire body to behave as a rigid body. This can be achieved by a contraction of most muscles. So in contrast with the time before the hand reaches the target, when most muscles should be relaxed, during the very short time of the impact most muscles must be contracted. In many Japanese martial arts this is somewhat confusingly explained by some mumbo-jumbo about "kime".