Haitō uchi, the ridgehand strike, superficially resembles the famous “karate chop,” but it uses the other side of the hand. There are three variations of a the ridgehand strike that you should familiarize yourself with, as we will show below:
To form the ridgehand (haitō), touch your thumb to fleshy part of your palm at the base of the little finger. The thumb side of the hand, minus the thumb itself -- the "ridge of the hand" -- is the striking point. Please refer to the photo below:
[Photo of a ridge hand from the top, and side, with a circle drawn around the haito.]
Rising ridgehand strike
Starting with your hand at your hip, rotate your arm forward from the shoulder. Do not lock your elbow. When your hand is in front of your shoulder, drop your elbow to snap your hand upward, striking the opponent's groin with your ridge hand.
[Video of rising ridgehands from the front and the side]
Downward ridgehand strike
This technique generates lots of momentum, and it will break something -- if it's not the target, then it'll be your arm. This is why downward ridge-hand strikes are rarely used in Goshin-Jutsu Karate. However, they are used in other martial arts (e.g., Tae Kwon Do, Tang Soo Do), so you must understand them in order to counter against them. Irimi-nage also incorporates a similar motion.
Starting with your hand at your hip, rotate your arm backwards from the shoulder. Do not lock your elbow. Continue for a full 270°, striking the opponent in front of you with your ridgehand from overhead. The motion is similar to the windmill strums 80's rockers used to play power chords, or the forward arm circles used to warm-up stretch before exercising.
[Video of downward ridgehands from the front and the side]
Inside ridgehand strike
Inside ridgehand strikes are sneaky techniques, because it appears to be linear technique, but it turns into a round technique at the last second, when it snaps. This is a fun technique to use during sparring; when the opponent is about to 7-3 outside, throwing one of these into their anticipated path will have a great effect.
Inside ridgehand strikes start out like front-foot or reverse punches, except that as they turn over, the hand opens into a haitō and cuts across your centerline, and into your opponent's neck, temple, or jaw.
[Video of inside ridgehands from the front and the side]
Keep your hand in front of your shoulder. Anything else is wildly flailing, not striking. When the hand is behind the shoulder, the body cannot absorb all of the impact energy, leading to shoulder injuries.