As your practice progresses, you can add force to your stretches. When this is done appropriately, it will be enjoyable, and will also be totally without strain or discomfort. When more force is applied, there will be greater muscle tone that increases the extension of the body. The structural details will remain the same, while there is a more active elongation of the spine, and a greater decompression of the joint spaces throughout the body.
For example, during Backbend over Roll, the arms may be actively stretched upwards away from the torso, while the legs are actively extending down away from the torso. This will significantly increase the overall stretch. The Spinal Elongation Breath in any of the exercises may be practiced more strongly. Even the conscious practice of the alignment principles described in Structurally Aligned Standing Posture can be practiced strongly as well, once the relaxed practice is well-learned by the body.
A stronger practice of any of the exercises should only be investigated once the body has already been opened to some degree, and you are comfortable with the practice details while more relaxed. If you develop the more active form of practice in any of the exercises, a particular practice session for that exercise may involve: first aligning the body in the exercise with relaxation, then smoothly adding more force, holding the stronger position for a time, then smoothly releasing the added force, until you are again in relaxed practice. You might do this several times during a particular exercise depending on its duration.
Slightly stronger practice can be held comfortably for longer than much stronger levels of practice; so as you increase the applied force, this will usually be intermittent, and not for the entire duration of practice of a particular exercise. Be sure to add or release increased force smoothly during practice (and during all other body use as well). Smooth application and release of force need not take more than a few seconds, but should not be sudden or abrupt. Your body sense will clearly direct you as to appropriate timing for increasing and decreasing internally applied force.
It is not necessary to develop the more active form of any of the exercises in order to derive tremendous benefit from their practice. As with the whole system, the active form of practice is best learned from a competent teacher.