Two Layers of Stretch
Gently drop the chin and place the hands on the back of the head as before. Now engage the muscles of the back of the neck and try to lift the head up. At the same time gently pull down on the head with the arms. You are now in a tug-of-war with yourself. Your arms are trying to pull the head down, but the neck muscles are trying to lift the head up.
In this experiment, you control both sides of this tug-of-war. You can allow the neck muscles to overpower the arm muscles and slowly raise the head. Or you can allow the arm muscles to overpower the neck muscles and slowly pull the head down.
If you try this experiment, you will discover that as long as the neck muscles are engaged, you will not be able to stretch the back of the neck completely. You should also feel that if you keep your head in a vertical position, your neck is stalemated between the effort to lift up and the effort to pull down. This muscular tension can become very vigorous, but there is no stretch on the joints of the neck.
This is the most important point of these demonstrations: if there is no stretch on the joints, then there is no stretch on the ligaments.
The Lower Spine
Sitting in a chair with hands on knees, passively drop forward to stretch the lower spine. As in the neck, the muscles are on the left and right sides of the spine and the ligaments are on the centerline. While bent forward, move the torso to the right to increase the stretch on the muscles on the left side. Moving the torso to the left, you can better stretch the muscles on the right side. Dropping straight forward, you can better isolate the ligaments.
You can increase the stretch of the lower spine by using your stomach muscles to round your spine. You can also do the opposite by using your back muscles to straighten the spine and lift the chest. By alternately rounding and straightening your spine, you can feel how rounding stretches the joints of the back and straightening prevents the joints from stretching.
As with the neck, you can engage in a tug-of-war between your stomach muscles and back muscles. One set of muscles is trying to round the spine, and the other is trying to straighten it.
As with the neck, the muscular tug-of-war between the stomach and back muscles can be vigorous. This can help develop muscular strength and control, but the joints of the lower spine are not stretching. If the joints are not stretching, then the ligaments are not being exercised.
Muscle and Ligament