Shotokan's Secret

Futi is the basic principle of wrist rotation. It is used in nearly all karate hand techniques.

You can recognize the karate sensei driving along in traffic because instead of snapping his fingers in time to the radio he snaps his wrist back and forth instead. This strengthens his futi, and at the same time drives his family crazy. I once woke up in the middle of the night to find that I had been practicing futi in my sleep by doing inside blocks against the bedstead. My wife was not impressed by my dedication.

There are two sides to futi. One is the sharp, snappy rotation of the wrist which puts a painful “edge” on blocks. The other is the fully-rotated focus which locks the punching wrist before impact. There might be something else, but futi has at least these two aspects.

• Futi is used to put a sharp “snap” into (nearly) all blocks. It is especially apparent in the inside and outside forearm blocks, but it is there in the other blocks as well. We use futi everywhere, just like we use hip vibration everywhere. Futi drives quite a bit of pain into the opponent’s punching arm, with little blowback into your own.
  
• As a focus technique for a front punch, futi is the ability to twist your wrist into the final position (palm toward floor, back of hand parallel to ceiling) without disconnecting the punch by rotating your elbow out to the side. This is extremely difficult to do, and when accomplished, it causes such a severe clenching of the forearm that all flexibility disappears from the wrist joint. Your arm feels like solid wood from the elbow to the knuckles. It isn't clear to me that this adds any power to the punch, but it seems to protect the wrist against spraining during impact.