Excerpted and some editing from "Uncovering the Treasure, Classical Tai Chi's Path to Health & Energy" by Stephen Hwa:
Please go to this link:
Internal Discipline Folding Movement Video Link
The folding move involves only one side of the body; but in this case it is not the entire side (includes legs which is shown in the photo above) which would be known as "hand follows foot , elbow follows knee", so please do not confuse this with that movement
This is just the upper quadrant of the body moving/folding as a unit. It is a QUARTER-BODY move. In the case shown in the video, the right side of the body is folding or unfolding by keeping the left side of the body stationary. The stationary part provides support, some of the power for the move but the lower 2 quadrants (legs) provide grounding. The Right side of the body is yang, the left side of the body is yin. The Yin-Yang junction is at the spine. One can visualize that the spine is a hinge, so each side of the torso, down through the buttocks is like a door which folds or unfolds using that hinge. If the leg was involved in the movement, it would be a HALF-BODY move.
Even though only a quarter of the body is moving it is still an important example of how to make a move but still keep a portion (in this case 3/4 of the body) still. It is also of importance as an example of how to make a move but keep a significant portion of the body alignment intact. Whether half body or quarter body, whether the leg moves with it or not it can only be achieved when the turning power comes from the waist and the entire back's muscles.
If this is done correctly , one will achieve a continuous energy flow in the body. It is a "neigong" exercise. It is tailor made to be a "silk reeling exercise" which might be defined as a continuous symmetrical simple internal movement or movements. Doing this, one will be able to learn gradually how to move with internal discipline and enjoy the sensation of internal energy circulation. This exercise emphasizes the stimulation of muscles, tendons and blood flow along the spine and the back. Those who practice this regularly experience a sense of rejuvenation and improved well being. If one has spare moments during the day, particularly if the exercise can be carried out in a casual and relaxed mood, there will be more chance for the subconscious to play a part. The ultimate objective is to learn internal movements like this in more or less a piecemeal fashion then integrate them into the Form play.