Hassō-shutō uchi literally translates as "all-eight directions knife-hand strike," because of it's versatility to hit different targets from different positions. This is the famous "karate chop", though within Goshin-Jutsu, hassō-shutō uchi, is commonly called a downward knife-hand strike.
Starting from a chambered position, raise the hand up along your torso to shoulder level. Then extend your arm directly forward, keeping your elbow pointed down, and your fingers pointing up, striking the opponent with your shutō. 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 up to shoulder level; like a scissor jack.