Hassō-shutō uchi, literally translates as "all-eight directions knife-hand strike," because of it's versatility to hit different targets from different positions. Within Goshin-Jutsu, hassō-shutō uchi, is commonly called a downward knife-hand strike, since that is the most popular version used in waza practice.
Starting from a chambered position, raise the hand up along your torso to collarbone level. Then extend your arm directly forward, keeping your elbow pointed down. At the same time, chamber the opposite-side hand.
[videos of hasu-shutos, fast and slow from the front and from the side.]
Do not hold your upper arm fixed in front of you, while madly swinging your forearm with the elbow alone, as though you were performing a culturally-insensitive baseball cheer; there is no power in such a technique. When performing hassō-shutō uchi correctly, the elbow moves from guarding the floating ribs, and up to shoulder level; it should resemble a scissor jack.