Riken-uchi

(back-fist strike). Actually, the striking surface here is the back of the two knuckles used in the straight punches. The elbow is pointed at the target, with the fist palm downward. Then, in the downward strike, the fist describes an arc in the vertical plane; in the sideways strike, in the horizontal plane. In both cases, the little finger side of the fist leads until the very last moment, when the fist is flicked over.