The Science

Polyarticular Chain Description

Polyarticular ChainTemporomandibular Cervical Chain (TMCC)

Muscles: Temporalis (ant. fiber), Masseter, Medial pterygoid, Rectus capitis posterior major, Obliquus capitis, Rectus capitis anterior, Longus capitis, Longus colli

Brachial Chain (BC)

Muscles: Anterior-Lateral Intercostals, Deltoid-Pectoral, Sibson’s Fascia, Triangularis Sterni, Sternocleidomastoid, Scaleni, Diaphragm

There are two brachial polyarticular muscular chains lying over the anterior pleural and cervical area. These chains influence cervical rotation, shoulder dynamics and apical inspirational expansion. They are composed of muscle that attaches to the costal cartilages and bone of ribs four through seven and xiphoid to the posterior, inferior occipital bone, anterior, inferior mandible and coracoid process of scapula. These two tracks of muscles, one on each side of the sternum, are anterior to the medial/upper mediastinum and upper thoracic cavity. They are composed of the triangular sterni, sternocleidomastoid, scalene, pectoralis minor, intercostals and muscles of the pharynx and anterior neck. They provide the support and anchor for cervical-cranial orientation, rotation and rib position. The right brachial chain muscle is opposed by the right posterior back muscles (PEC), lower trap, serratus anterior, external rib rotators and left internal abdominal obliques. The brachial chain muscle on the left is opposed by the left posterior back muscles (PEC), lower trap, serratus anterior, external rib rotators and right internal abdominal obliques.

Anterior Interior Chain (AIC)

Muscles: Diaphragm, Iliacus, Psoas, TFL, Vastus Lateralis, Biceps Femoris

There are two anterior interior polyarticular muscular chains in the body that have a significant influence on respiration, rotation of the trunk, ribcage, spine and lower extremities. They are composed of muscles that attach to the costal cartilage and bone of rib seven through 12 to the lateral patella, head of the fibula and lateral condyle of the tibia. These two tracts of muscles, one on each side of the interior thoraco-abdominal-pelvic cavity, are composed of the diaphragm and the psoas muscle. With the iliacus, tensor fasciae latae, biceps femoris and vastus lateralis muscles this chain provides the support and anchor for abdominal counter force, trunk rotation and flexion movement.

The Left AIC & Right BC Polyarticular Pattern

Individuals experiencing symptoms at the knee, hip, groin, sacral-iliac joint, back, top of shoulder, between the shoulder blades, neck, face or TMJ will demonstrate inability to fully adduct, extend or flex their legs on one or both sides of their body. They usually have difficulty in rotating their trunk to one or both directions and are not able to fully expand one or both sides of their apical chest wall upon deep inhalation. Cervical rotation, mandibular patterns of movement, shoulder flexion, horizontal abduction and internal rotation limitations on one or both sides will also complement the above findings. Postural asymmetry will be very noticeable with one shoulder lower than the other and continual shift of their body directed to one side through their hips.

The pattern that is most often prevalent involves the left anterior interior chain, right brachial chain and right posterior back muscles (PEC) of the body. The left pelvis is anteriorly tipped and forwardly rotated. This directional, rotational influence on the low back and spine to the right, mandates compulsive compensatory movement in one or more areas of the trunk, upper extremities and cervical-cranial-mandibular muscle. The greatest impact is on rib alignment and position, therefore influencing breathing patterns and ability. Respiratory dysfunctions associated with asthma or daily, occupational or repetitive work positions can also influence pelvic balance and lead to a compensatory pattern of an anteriorly tipped and forwardly rotated pelvis on the left.

Other common, objective findings secondary to compensatory physical attempts to remain balanced over this unlevel pelvis include elevated anterior ribs on the left, lowered, depressed shoulder and chest on the right, posterior rib hump on the right, overdeveloped lower right back muscle, curvature of the spine and asymmetry of the head and face.

This particular pattern of neuromuscular imbalance is enhanced and generated usually at early ages of development in the pre-adolescent and adolescent years. Since the fibers from our diaphragm that attach to the front of low spine and our diaphragm in general is stronger on the right, we all have a tendency to shift and rotate our spine to the right sooner and more often than to the left. The liver also assists this directional pull on the spine and pelvis because it keeps the right larger diaphragm better positioned for respiratory activity. We do not have a liver on the left side. The left diaphragm leaflet is much smaller and does not have the advantage to pull the ribs up and out upon inhalation. There is a tendency to relax the left abdominal wall. Consequently, these abdominal muscles on the left become weak.

This pattern complements our right dominance of extremity use, our daily shifting of weight to the right and overcompensating patterns of activity concerning our pelvic floor. Airflow, for example, will generally move more easily into the left chest wall than into the right because of the rotational influence of the ribs, as previously described. Lack of underlying structural support exists on the right that does not exist on the left due to pericardium position. Rotation of the upper trunk to the left will generate less activity on the neck when in this pattern because of this dynamic, respiratory, structural phenomena. However, rotation of the upper trunk to the right limits air movement into the left chest wall. This created torque on soft tissue, secondary to movement on an imbalanced foundational structure, usually results in chronic muscle overuse, inflammation and pain similar to fibromyalgia.


ZOA Position & Mechanical Function

The diaphragm’s mechanical action and respiratory advantage depends on its relationship and anatomic arrangement with the rib cage8,16. The cylindrical aspect of the diaphragm that apposes the inner aspect of the lower mediastinal (chest) wall, constitutes the zone of apposition. Its region extends from the diaphragm’s caudal insertion near the costal margin, cephalid to the costophrenic angle, where the fibers break away from the rib cage to form the free diaphragmatic dome16,17. The area of apposition of diaphragm to rib cage has a cephalad extreme at the beginning of dullness by percussion and a caudal extreme just above the costal margin16. For many of us the cephalid extreme begins immediately below T8 or below the cephalid aspect of the diaphragm’s dome. The zone of apposition, for the most part, is not influenced by height of diaphragm dome but rather by the orientation of the rib cage. Individuals with elevated anterior, externally rotated ribs will have a decrease in their zone of apposition on one side or both sides of their thoraco-abdominal, depending on their pattern of diaphragm opposition, abdominal weakness and use.

The area of apposition of diaphragm to rib cage makes up a substantial but variable fraction of the total surface area of the rib cage. It accounts for more than one half of the total surface at residual volume and decreases to zero at total lung capacity16. During quiet breathing in the upright posture, it represents one fourth to one third of the total surface area of the rib cage16. The zone of apposition has anatomic importance because it is controlled by the abdomen and oblique muscles and directs diaphragmatic tension. Accessory respiratory muscle overuse, chest wall mobility and lung hyperinflation are all influenced by diaphragm and zone of apposition resting positions at the end of exhalation10.

The rib cage and abdominal pathway are therefore always mechanically coupled through the zone of apposition1. Abdominal muscle resting tension opposes the inspiratory action of the diaphragm by facilitating an increase in pressure in the abdominal compartment rather than outward protrusion of the abdomen during diaphragmatic contraction19. Therefore, the zone of apposition and dome shape of the diaphragm are maintained during inspiration by abdominal muscle resting tension supporting the abdominal viscera and stomach up against the diaphragm’s undersurface.

In summary, the dome of the diaphragm corresponds to the central tendon and the cylindrical portion corresponds to the portion directly apposed to the inner aspect of the lower rib cage called the zone of apposition. In relationship to its function, the diaphragm can be considered as an elliptical cylindroid capped by a dome (see figures). In standing humans at rest, this zone of apposition represents about 30 percent of the total surface of the rib cage. When the diaphragm contracts during inspiration its muscle fibers shorten. The axial length of the apposed diaphragm diminishes and the dome of the diaphragm descends relative to its costal insertions. The height of the zone of apposition in normal subjects actually decreases by about 1.5 cm during quiet inspiration, while the dome of the diaphragm remains relatively constant in size and shape. Thus, the most important change in diaphragmatic shape, the one responsible for most of the diaphragmatic volume displacement during breathing, is a piston-like axial displacement of the dome related to the shortening of the apposed muscle fibers5. The most important change in diaphragmatic change, ie shortening of the apposed diaphragm muscle, is also dependent therefore on opposition of the anterolateral abdominal muscle for diaphragmatic respiratory mechanical advantage, action and position11.

ZOA Restoration

Apposition of the diaphragm can be lost unilaterally, almost always on the left or bilaterally; resulting in a left Anterior Interior Chain pattern (L AIC) or Posterior Exterior Chain pattern (PEC), respectfully.

Abdominal muscle, internal obliques and transverse abdominis are primarily responsible for ipsilateral diaphragm leaflet opposition and for ipsilateral lower leaflet opposition upon contraction during inspiration, resulting in contralateral upper rib cage and apical chest wall expansion, especially during trunk rotation or gait. Loss of ipsilateral or bilateral abdominal opposition and diaphragm apposition results in hyperinflation. Studies have demonstrated that changes in diaphragm dimensions produced by chronic hyperinflation occur exclusively in the zone of apposition. Contraction of the diaphragm has been demonstrated to reduce the proportion of surface area apposed to the rib cage³.

Reducing physical and physiological symptoms associated with hyperinflation, paradoxical breathing and accessory respiratory muscle overuse requires repositioning and re-training of the diaphragm for normal zone of apposition activity.

Using the Postural Restoration Institute® L AIC manual technique, one can guide the rib cage and diaphragm into a position where the left leaflet of the diaphragm regains proper mechanical advantage to efficiently contract via the central tendon and where the dome can rest at expiration since tangential force is no longer needed for postural stabilization.

Proper position of the diaphragm is reached when expansion of the abdominal wall is no longer required during maximal opposition (internal rotation of the ipsilateral rib cage) at inspiration. Although simultaneous “belly” expansion and chest wall expansion is desirable upon inhalation via the nose without using accessory muscles of the neck; contralateral apical flexibility and chest wall mobility is needed during ipsilateral diaphragm apposition contraction for diaphragmatic breathing to occur effortlessly with assistance from external barometric pressure, chest wall re-coil, pleural elastic properties and negative internal mediastinal pressure.

A good example of active established ZOA occurs when one can perform a successful standing reach test, fingers to toes in standing, and inhale with anterior mediastinal compression and posterior mediastinal expansion. Passive ZOA can be reached through PRI manual techniques, if active ZOA is unobtainable. Maximum ZOA is completed passively, in supine, when at the end of the exhalation phase the trans-diaphragmatic strength during active ZOA contraction is the strongest at thoraco-lumbar flexion and the weakest at thoraco-lumbar extension. At the end stage of a L AIC manual restoration technique the anterior lower leaflet of the sighing patient will easily depress caudally and “drop” posteriorly, through internal rotation of the rib cage.

ZOA References

To read more peer reviewed journal articles about PRI click HERE.

What Is Posture?

Posture is the reflection of patterned airflow.

Airflow is a reflection of the “position” of many systems that are regulated, determined and created through limited functional patterns. These patterns reflect our ability and inability to breathe, rotate, and rest, symmetrically with the left and right hemispheres of our axial structure.

“Limited functional patterns” refers to movement that is restricted in directions, planes or normal boundaries of functional range, as a result of improper joint, muscle, and mediastinum rest position. Function is therefore limited because soft tissue and osseous restrictions prevent one from using muscles and joints in their normal range. Adaptation and compensation for these limitations require neuromotor encoding and hyperactivity of muscle that is placed in improper positions that exceed normal physiological length, or in positions that make them a mover or counter-mover in planes and directions that are not observed when one is in a neutral or more symmetrical state of rest. This compensatory activity and hyperactivity usually becomes dysynchronous in the accessory muscles of respiration and at the appendicular flexors and axial extensors, thus limiting functional rotation at the trunk and through the lumbo-pelvic-femoral and cranial-mandibular-cervical complex. - Ron Hruska Jr., MPA, PT