A principle function of the sacroiliac joint is to transmit the weight of the trunk and arms to the legs, while also transmitting ground forces in the reverse direction. In this sense, it serves as the central point of movement in weight transfer, shock absorption, and cranio-sacral motion.

Muscular Influence on Sacroiliac Movement
Most of the muscle groups in the body attach to the sacrum and/or innominate bones, yet muscular influence on movement of these bones has long been disputed. In fact, some anatomy books list the function of muscles that attach to the pelvis only by how they influence the extremities or spine, while ignoring their effect on the pelvis; as if the pelvis is a non-moveable base that anchors the muscles. However, research [1, 2] has demonstrated that afferent information from the pelvic ligaments can influence muscle activation patterns to move the pelvis and lumbar spine.

Accordingly, the Serola Theory proposes that sacroiliac joint movement occurs through forces generated by the muscles that attach to the sacrum and/or innominates. Each muscle, depending on its attachment points and angles of pull, acts through independent vectors to induce either nutation or counternutation, not only at the sacroiliac joint, but throughout most of the musculoskeletal system. The movement pattern is in accordance with the alignment of the articular (synovial) region but is regulated by the ligaments, which are mostly derived from the syndesmosis (ligamentous) region. Table 1 accompanies the descriptions of some muscles, along with their origin, insertion, and action of promoting either nutation or counternutation.
One important thing to recognize is that muscular activation, or inhibition, patterns occurring in nutation and counternutation, express the natural coordination that is inherent during respiration, gait, craniosacral motion (cerebral spinal fluid flow) and musculoskeletal response to injury. The motion of nutation and counternutation is an unconscious, innate movement pattern apparent in the similar muscle firing patterns evidenced in these different movements. Although each is a separate system, and occurs independently, either can influence the others. Although innate, each may be altered by superimposing one’s will upon the system. By varying movements, load, posture, rate of walking, or breathing, or by restricting or mobilizing the sacrum or cranium, one can influence the rate and depth of movement.

In the Serola Theory, I have created many animated videos that depict the role of individual muscles in inducing nutation or counternutation, with descriptions of their origins, insertions, and functions, as well as information from the medical literature on various aspects of their applications to my theory.

Respiration
Comroe & Schmidt [3] demonstrated that respiration was affected by limb movement and the influence came from structures within the joints. This indicates a proprioceptive signal from the joint ligaments influencing breathing rate and/or depth.

Ro [4]p226 described the action of muscles while breathing. During inspiration, the (deep) erector spinae contract and the rectus abdominis and pelvic diaphragm relax, resulting in the innominates being pulled into anterior tilt (counternutation). During expiration, the rectus abdominis and pelvic diaphragm contract and the (deep) erector spinae relax, therefore the innominates are pulled into posterior tilt, while the sacral base moves anteriorly and inferiorly (nutation). Respiration alone, at about 12 to 20 breaths a minute, occurs about 20,000 times a day.

Note: there is some misunderstanding as to the function the pelvic diaphragm muscles, of which the piriformis is a part. Although, in Ro’s study, they contract during expiration as part of a stabilization group to hold the trunk motionless, they are actually counternutators and contract during the movement of inspiration. It is only when movement stops, and stabilization begins, that the pelvic diaphragm contracts regardless of whether the person is in inspiration or expiration. Because the contraction in stabilization is stronger than in regular movement, it may appear to relax in inspiration if measure relative to each other. (See Stabilization Groupings)

Mitchell & Pruzzo [5] used double exposed x-rays of 32 subjects during normal inhalation and exhalation. They measured the position of the sacral apex relative to the ischial spine. Their findings demonstrated that the sacrum moves into nutation on exhalation and counternutation on inhalation.

Gait
Gracovetsky & Farfan [6], using electromyography (EMG), found a pattern of trunk movement controlled by muscular actions during gait. Although their discussion is about gait, we can look at it as an example of an alternating nutation/counternutation pattern. In their example, left sided muscles develop a counternutation pattern while, concurrently, right sided muscles develop a nutation pattern. They state: “As the left leg advances and the right leg is in extension, contraction of the lateral flexors forces the spine to flex to the left, as viewed from the back. The left facets engage and the spine flexes as it bends to the left thereby reducing lordosis. The coupled motion of the spine induces a clockwise torque, as viewed from above, as well as the reduction in lordosis. Hence, when viewed from above, L5 rotates clockwise with respect to L1. Therefore, the pelvis rotates clockwise, and the left hip moves forward, while the trunk, shoulders, and upper extremities move in the opposite direction. The counter-rotation of the shoulders is enhanced by the simultaneous action of the right pectoralis major, anterior deltoid, and anterior serratus, and the action of the left trapezius, posterior deltoid, and latissimus dorsi. The left shoulder moves backwards, as the spine winds up and flexes to the left.”

In the above example, a left counternutation pattern occurs as the spine bends and rotates to the left and the left lumbar curve straightens. The muscles that develop counternutation on the left are the left trapezius, posterior deltoid, and latissimus dorsi, which pull the left shoulder backward. The muscles that develop nutation on the right are the right pectoralis major, anterior deltoid, and anterior serratus, which pull the right shoulder forward.

Once the limit of motion is reached, the spine begins to rotate to the opposite direction. Gracovetsky & Farfan continued by stating that “When the spine derotates, it is necessary to increase the lordosis (on the left), maintain axial compression, and reduce shear. This can be done by an inferior and anterior pull on the convexity of the spine (on the right side). The right psoas is the only muscle that can perform this task. The psoas-induced and controlled axial counterclockwise torque generates a lateral bend to the right (counternutation shifts to the right). This effect is enhanced by the combined action of the (right) erectores, the right latissimus dorsi, and (right) trapezius. The resulting torque reverses the pelvic motion” [6].It should be noted that the right psoas creates a counternutation response, inducing an increased lordosis on the left while decreasing the lordosis on the right. Gait occurs at about 2,000 steps per day, which puts significant stress into the sacroiliac joint.

Shock Absorption
In gait, as the right heel strikes the ground, the weight of the upper body is held by the sacrum, forcing the right side of the sacrum to move inferiorly and anteriorly. A corresponding ground reaction force is transferred up through the right leg to the pelvis where it forces the right innominate to rotate superiorly and posteriorly. Both forces induce nutation on the right side. At the same time, the left side of the pelvis goes into counternutation. As one continues, and the left heel strikes the ground, the forces are reversed. This alternating left/right nutation/counternutation movement travels superiorly though the spine to the head, in a rhythmic oscillation. Similarly, the reverse motion can occur inferiorly through the spine to the legs [6]. The same pattern will occur with any axially directed force. Whether lifting an object, braking hard, climbing a ladder, or landing on one’s feet, the force transmitted will create a nutation effect at the center of the body’s shock absorption system, the sacroiliac joint.

Cerebral Spinal Fluid Pumping Mechanism
Another mechanism of influence to cranio-sacral movement was discovered by an osteopath, W.G. Sutherland, and later proven by another osteopath, Viola M. Frymann. In her study, Frymann [7] studied cranial movements with extremely sensitive instrumentation. On May 30, 1973, she recorded the “first unmistakable recording of a cranial rhythmic impulse”. She stated that “The recordings show that there is a cranial motility slower than and distinguishable from the motility of the vascular pulse and thoracic respiration, and that such motion can be recorded instrumentally. She went on to comment “The perpetual outpouring of impulses from the brain to maintain postural equilibrium, chemical homeostasis, and so on conceivable may multiply the activity of individual cells into a rhythmic pattern of the whole brain, small enough to be invisible to the naked eye, but large enough to move the cerebrospinal fluid, which in turn moves the delicately articulated cranial mechanism.”

DeJarnette, a chiropractor and osteopath, along with other craniopaths, have taught that the movement of cerebral spinal fluid, which bathes the brain and spinal cord, is coordinated with reciprocating movement of the cranium and sacrum. DeJarnette says that this movement is felt to be at about 9 pulses per minute (8-14/minute), for about 13,000 movements per day,
whereas respiration is about 14 pulses per minute (12-20/minute)

Even with Frymann’s study, there is still considerable controversy within the research community about whether this mechanism actually exists independently of respiration and cardiac rhythms. The considerable skill needed to determine and separate the different types of motion leaves room for doubt with those who have not acquired the necessary skill. However, there are both chiropractic and osteopathic techniques that, through gentle and sensitive palpation, are able to identify and manipulate cranial motion, freeing locked segments and balancing cerebrospinal fluid flow.

References:
1. Indahl, A., et al., Sacroiliac joint involvement in activation of the porcine spinal and gluteal musculature. Journal of Spinal Disorders, 1999. 12(4): p. 325-30.
2. Tichy, M., et al., Pelvic Muscles Influence the Sacroiliac Joint. Journal of Orthopaedic Medicine, 1999. 21(1).
3. Comroe, J., Jr. and C. Schmidt, Reflexes from the limbs as a factor in the hypernoea of muscular exercise. Amer. J. Physiol., 1943. 138: p. 536-547.
4. Ro, C.-S., Sacroiliac Joint, in Low Back Pain, J.M. Cox, Editor. 1990, Williams and Wilkins: Baltimore, MD. p. 214-242.
5. Mitchell, F.L., Jr. and N.A. Pruzzo, Investigation of voluntary and primary respiratory mechanisms. J Am Osteopath Assoc, 1971. 70(10): p. 1109-13.
6. Gracovetsky, S. and H. Farfan, The optimum spine. Spine, 1984. 11(6): p. 543-73.
7. Frymann, V.M., A study of the rhythmic motions of the living cranium. J Am Osteopath Assoc, 1971. 70(9): p. 928-45.