KempoJuJitsu stated:
Theres a movement after the "down block and several "inward blocks" your hand is on the inside of your arm. Right at the elbow joint. Using the method
Naihanchi is so rich in application, there are lots of potential applications at the point you mention above.
I see from your profile that you have a grappling background. So instead of trying to describe one against a standing opponent, I will give you something you can probably readily relate to.
Some preliminaries.
Each sweeping kick is followed by a big turn of the torso, but the arms basically don't move in relation to the torso. And the hips stay relatively in place. The shoulders rotate way further than the hips. This is not obvious in all systems, but it is clear in the Matsubayashi videos that RyuShiKan has provided a link for. Shotokan, also has a big movement.
One of my students trained previously in a Shotokan dojo that had a wonderful exercise for improving this turn of the torso. Two students would line up in Naihanchi dachi, back to back but not touching. One would have a big ball. They would rotate towards each other to one side and pass the ball, and then rotate in the other direction and do the same. Back and forth with the torsos. Passing the ball faster and faster.
Back to the movements. In many of the forms, as you rotate side to side, both arms move in unison. In some systems one hand touches the other arm, and in some systems they are separate. The Motobu gif shows the arms connected.
http://www.geocities.com/uchinati/kata.html
Now to ground fighting. First we will look at a simple ground and pound application from the mount (for the non-grapplers, on top). On the ground, like in naihanchi, your hips are, at times, pretty immobile, and you rely on your torso for power.
Let's say the opponent beneath you strikes with his right. Then you will pivot to your left, with your left hand up and your right arm flat across your torso. As you pivot to your left (counterclockwise) with your torso, the left arm blocks the opponent's right strike and your right elbow strikes the head/neck. The kata repeats in rapid succession to the other side. Here you can grab your left hand with your right hand for extra power. In fact, the kata then stacks the hands and counterpivots again with a double strike. That's a third elbow (your right), all with the torso for power. Or if the opponent has both hands out and strikes with one and then the other hand, you merely elbow the head with each block.
So you have a simultaneous block and strike (with the elbow to the head,) followed by an immediate second and perhaps third elbow to the head. In this movement, your hips are relatively stationary and your torso moves fully, just as in the kata. The actual position of your legs is quite a bit like Nainachi. Finally, you are using your elbows to strike the head and not your knuckles. Elbows are pretty resilient, especially compared with the finger bones below the knuckles which tend to break when hitting the jaw, cheekbone and brow.
There are other applications as well. The close-in arm on this can also be used to choke. Let's say it is the left arm with the hand at the elbow and the right arm has the hand high. Then you use your right forearm to drive your right hand down on one side, while you use your weight to drive your elbow down to the ground with the other.
How about another basic ground fighting technique. Let's say you block a strike and want to bring the striking arm up under your stomach to pin it and keep it out of the way. The first pivot brings both hands out towards the striking arm. Then both try to wrap/grab the arm and once engaged, you use the reverse torso rotation to drive the hand across his torso to pin it. If the opponent tries striking with the other, while you are doing this, your natural pivot towards that arm sets up a block.
Now lets go to the guard (on the bottom) with the attacker in the mount position. A common move in Ju Jitsu is to reverse position or pass the guard and proceeds is as follows:
Against a straight right arm next to our head (could be supporting weight, or could have just punched), you wrap the left arm over and around to set up a lock, and you bring your left foot underneath you, up as close to your groin as you can. Then you simultaneously rotate to your right and push off with your left foot. The rotation enables you to successfully push your right hand against the attackers neck, and work a good arm bar with your left. You roll over the top and reverse the guard.
Here is Naihanchi. The sweep to your left puts your foot in position for the reversal (leave it there). The rotation to the left uses the left arm to wrap and the right arm to either elbow (if the head is down, or just get in position for the following push to the neck. Then the rotation to the right accompanies the drive of the left leg down to make the reversal.
We can go on an on regarding ground fighting ideas. Yabu Kentsu said, "Karate begins and ends with Naihanchi". It seems like there are an endless supply of meaningful applications.
What do you think?