When performing blocks or strikes that utilize the arms, one arm typically moves out to either meet the target or to intercept the attack while the other is pulled back to what is often referred to as the chamber position, either the top of the hip bone or the floating ribs. In either case, the pulling hand refers to the hand being pulled back rather than the hand that is moving out. These two actions occur simultaneously.
Putting the concept of the pulling hand into practice, leading with the elbow the pulling hand should be pulled back forcefully so that it stays as close to the body as possible and that it travels the shortest possible distance back to the chamber position. Having been pulled back, the hand should finish in the chamber position, pressing strongly against the body. At this point, the elbow should be pointing directly back, squeezing slightly towards the centre of the back, while the top of the knuckles are facing down towards the ground and the thumb is facing up to the ceiling. Since the knuckles are now pointing downwards to the ground, it is necessary to twist the fist during the pull back. This twist should begin immediately as the arm is drawn back and should finish as it reaches the chamber position. From the chamber position, if you were to look straight ahead into a mirror, the elbow should not be visible.
In terms of why one would want to employ the pulling hand concept, there are certain benefits but it is important to understand that these benefits are accompanied by tradeoffs. In particular, in the beginning and intermediate levels the pulling hand is essential to maximize the instigation and synchronization of large torso muscle groups that then effect the technique being delivered (Dr. Ingber, 1981). This is the primary reason that the use of the pulling hand will be heavily emphasized until the student reaches an advanced level.
Another reason given by many instructors supporting the use of the pull hand is that it increases balance and adds rotational power. The theory underlying the balance argument is that for every action there is an equal and opposite reaction (Newton’s Law). This seems reasonable, but at the same time, I personally have never noticed any reduction in my balance if I did not use the pulling hand in performing a technique. In terms of adding rotational power, the effect of the pulling hand is minimal once the students have learned how to properly apply the power generation method.
Other possible benefits in using the pulling hand is that it can be used to stabilize an opponent for an attack, it can help inhibit the opponent from attacking by trapping one of his limbs, and that a big pull back motion also leaves the back hand in a position to deliver a very strong follow-up technique. However, at the same time, using a big pull back motion will leave the back hand in a position where it is not useful to defend. A point of that must not be ignored, this is the main drawback of the pull hand concept.