Seiken

Making a fist, or Seiken, correctly is important in avoiding injury. Starting with the fingers fully extended and the thumb pointing upwards, fold the four fingers at the first and second joints until the fingertips touch the base of the fingers at the third joint. The fingers should be drawn in tightly. Continue to draw in the fingers until they are pressed tightly into the palm. The thumb is then folded firmly over the fingers and pressed against the index and middle fingers. 

If the thumb is not tucked in, it can get caught and damaged during contact. The thumb also provides support for the fingers. The thumb should never be extended over the top of the index finger. Finally, it is important that the forearm, wrist and fist form a straight line. If this is not done, the pressure on an angled wrist can cause serious damage. Contact is generally focused on the first knuckle of the index and middle fingers.