Starting from kamae ensure that you are not holding the mokuju too tightly. Perform the thrust with the hands moving in the straightest line to their final position.
As the thrust concludes ensure that you have “shimeru”. This is where everything is locked in position. From kamae to strike there should be no extra movements.
The front hand holds the mokuju between the two white lines. The V formed by the thumb and forefinger is along the line of the barrel and above it. Note carefully that the wrist doesn’t change position when striking as shown at 26 seconds. Rolling the wrist over is incorrect. Not maintaining the same position of the wrist also creates extra movements which will slow down the strike and hinder the final locked position.
At the end of the strike the barrel of the mokuju should be horizontal. Poetically speaking a drop of water should slowly roll down to the point or nose of the mokuju. If the nose of the mokuju is even slightly above horizontal your strike will be weaker. At 20 seconds Terada sensei demonstrates the “nose up” style of strike. As you can see the smallest angle above horizontal is easily noticeable and wrong. The rear hand should be in the area of your left nipple. Pay careful attention to the rear wrist, note that it is straight. If your wrist is bent when striking the impact will jar your wrist and you will likely end up with a very sore wrist. The left arm should be straight, if it is hyperextended you will again hurt yourself and if it is bent you will not achieve the locked position required for a good strike.
The backhand has the forefinger in front of the trigger and all fingers maintain contact with the mokuju. At 37 seconds you can see the mistake that Simon (thanks sensei – sl) often makes where his forefinger is not in contact with the mokuju. When in kamae the grip should be relaxed without strength or tension. Too much tightness in the grip will make the mokuju movements jerky and slow. Only as the strike concludes does the back hand tighten to provide the locked position required for a powerful strike.
When placing your rear hand on the mokuju do not place it from above. As you can see at 1:27 having the hand on top of the mokuju places the wrist and elbow in a position where they will have to be adjusted before the strike can be made. Instead grasp the mokuju from the side, tilt the mokuju 15 degrees and ensure the rear elbow is clear from the body. This way a strike can be made with minimal movement. Note that if your elbow is tucked in against your body it may be contributing to a bent rear wrist when striking so if your right wrist hurts double check your elbow placement in kamae.
Assuming you have your hands placed correctly and that you are standing side on to the opponent (hanmi) you shouldn’t have any holes or openings in your guard. Refer to the Kamae video showing how Terada sensei in kamae covers his target areas completely for more on this.
Remember to move your hands from kamae to the strike position in the straightest line possible. If your kamae is correct this will mean the point (kensaki) of the mokuju will move in a straight line as well. Straight lines are fastest.