In basic defensive techniques, the retreating hand first goes forward as far as possible and the defending hand goes backward as far as possible. This makes the performer compact, closed, "small" when lunging.
Before completing the technique, the arms are quickly pulled in the opposite direction so that the retreating hand is stopped at the back of the hip and the defending hand is accelerated forward to the end point of the technique with a powerful tension. This makes the performer "big." This contrast - small-big - allows for maximum force due to the long distance. The generated interaction of the retracting arm and the performer, further amplifies the force that hits the target.
Here you will find all information about the techniques in the video