**2.5. Synchronicity of respiration and gait**

The right hemipelvis configuration is opposite relative to the left; it is posteriorly rotated. The right lateral abdominals are better positioned to exhale, but are more restrictive to inhale. Compensatory strategies to maximize breathing capacity in order to meet respiratory need will then rely on the accessory muscles of respiration, including the psoas, paraspinals, muscles of the upper back, chest, and anterior neck. With these compensatory changes in breathing mechanics, left anterior ribcage flares and right anterior ribcage restriction may progress along this diagonal trajectory, resulting in the common scoliosis pattern of right posterior ribcage prominence and left posterior ribcage concavity [1–4]

**2.4. Right-side dominance, the functional result of physiological asymmetry**

Humans almost universally exhibit right-dominant postural and movement patterns resulting from physiological asymmetry. Preferential standing on the right leg and increased breathing efficiency of the right hemidiaphragm are major contributors to this fundamental bias. Additionally, 90% of the population is right-handed, a defining characteristic of humans [11, 15]. Use of the right upper extremity for manipulative and reach activity dates far back in human history and has been correlated with early human brain asymmetrical development [11]. Right arm swing accompanies right stance phase of gait and coordinates with left leg swing-through. Right arm swing, consistent with right reach activity, promotes left trunk rotation to balance lumbar spine and pelvis right orientation, present in right unilateral stance. However, it is important to emphasize that handedness does not define side dominance [34]. Left-right asymmetry is a fundamental, ancient characteristic of animal development present in the earliest large multicellular organisms according to fossil records [14, 34]. Strong right-hand preference for manipulative and expressive tasks is thought to correspond to the emergence of language. These developments occurred with

**Figure 5.** (A) EOS of common scoliosis pattern used with permission. (B) Common costal deformity in scoliosis used with permission from The Martindale Press, Three Dimensional Treatment for Scoliosis, 2007 by Lehnert-Schroth, C.

(see **Figure 5A** and **B**).

142 Innovations in Spinal Deformities and Postural Disorders

During breathing, the thoracic diaphragm and the pelvic diaphragm (pelvic floor muscles) function synergistically, linking gait and respiration [4, 36]. Internal obliques and transverse abdominis muscles are key participants in this process. Acting as a force couple, these lateral abdominals assist the hamstring's postural activity to maintain a neutral pelvis position as they simultaneously assist ribcage position and motion [25, 26, 31, 37]. Concurrently, lateral abdominal and hamstring lengths are determined by pelvic position due to their respective pelvic insertions.

When the thoracic diaphragm descends for inhalation, the abdominal muscles and the muscles of the pelvic floor *eccentrically* lengthen to allow for visceral displacement caudally [16]. As the abdominal muscles elongate, the ribcage expands and externally rotates, and the pelvic crest migrates forward into anterior rotation, abduction, and external rotation, while the ischial tuberosities approximate, allowing the pelvic floor to descend. The femur remains oriented anteriorly to keep the feet in a forward trajectory. Relative to the acetabulum, the femur is in an externally rotated *unlocked* position, described as "Acetabular Femoral External Rotation" (AFER), which facilitates the swing phase of gait [1–4] (see **Figure 6**).

**Figure 6.** Frontal view of left AFER and right AFIR illustration created by Elizabeth Noble for the PRI copyright. Used with permission from the PRI®. Copyright 2017, www.posturalrestoration.com

Active exhalation relies on *concentric* activation of the internal obliques and transverse abdominis muscles to assist ribcage contraction, internal rotation, and thoracic diaphragmatic ascension. As the lateral abdominals shorten, they assist posterior rotation, adduction, and internal rotation of the pelvis. This pelvic position assists ascension of the pelvic floor as the ischial tuberosities move laterally as pelvic crests move medially [4, 25, 26]. The two diaphragms coordinate their pistoning activity, moving as a unit cephalically on exhalation and caudally on inhalation. While the pelvis rotates posteriorly with adduction and internal rotation, the stance leg maintains its forward orientation. The now internally rotated configuration of femur to acetabulum, described as "Acetabular Femoral Internal Rotation" (AFIR), *stabilizes* the hip joint (see **Figure 6**). Muscles of the hip—hamstrings, adductors, and gluteals—synchronize with lateral abdominals to stabilize the pelvis [1–4].

These functional relationships occur during gait. Gait is a highly complex movement task, which requires multisystem coordination and integration. Visual-vestibular, somatosensory, respiratory, and cardiovascular systems all give input and guidance [38]. Biomechanically, the challenge is to stay upright as the body advances through space balanced over one limb. When one side is in stance phase of gait, the contralateral side is in swing phase. The opposite arm and leg swing forward together (see **Figure 7**). This reciprocal extremity activity balances the torso around a vertical axis and assures nonstressful upright balance. In stance phase, the pelvis and lumbar spine are rotated toward the stance leg. The trunk is rotated opposite to the stance leg at or above the upper aspect of the diaphragm and is side bent ipsilaterally due to ipsilateral forward arm swing and ribcage kinematics [39]. This configuration mechanically supports shortening of the stance leg side abdominals, further assisting ribcage contraction and diaphragmatic ascension. Efficient gait requires the right and left sides of the body to be relatively equally competent in both stance and swing phases of gait. Gait is the best measure of balanced, biomechanical asymmetry [2].

**Figure 7.** Alternating reciprocal gait viewed from above used with permission from the Postural Restoration Institute®. Copyright 2017, www.posturalrestoration.com

However, anatomical and physiological asymmetry biases the body toward greater competency in right stance. When musculoskeletal function is not relatively balanced, the left side does not achieve full stance phase of gait or full exhalation phase of respiration, and the right side will likely not achieve effective swing phase of gait or efficient inhalation phase of respiration. The daily repetitive nature of these basic activities of life reinforces and strengthens unbalanced asymmetrical function. Without intervention, the unequal stresses placed on musculoskeletal elements will likely progress to structural changes.

#### **2.6. Muscle chain activity of the right-side dominant pattern**

and internal rotation, the stance leg maintains its forward orientation. The now internally rotated configuration of femur to acetabulum, described as "Acetabular Femoral Internal Rotation" (AFIR), *stabilizes* the hip joint (see **Figure 6**). Muscles of the hip—hamstrings, adductors, and gluteals—synchronize with lateral abdominals to stabilize the pelvis [1–4]. These functional relationships occur during gait. Gait is a highly complex movement task, which requires multisystem coordination and integration. Visual-vestibular, somatosensory, respiratory, and cardiovascular systems all give input and guidance [38]. Biomechanically, the challenge is to stay upright as the body advances through space balanced over one limb. When one side is in stance phase of gait, the contralateral side is in swing phase. The opposite arm and leg swing forward together (see **Figure 7**). This reciprocal extremity activity balances the torso around a vertical axis and assures nonstressful upright balance. In stance phase, the pelvis and lumbar spine are rotated toward the stance leg. The trunk is rotated opposite to the stance leg at or above the upper aspect of the diaphragm and is side bent ipsilaterally due to ipsilateral forward arm swing and ribcage kinematics [39]. This configuration mechanically supports shortening of the stance leg side abdominals, further assisting ribcage contraction and diaphragmatic ascension. Efficient gait requires the right and left sides of the body to be relatively equally competent in both stance and swing phases of gait. Gait is the best measure

However, anatomical and physiological asymmetry biases the body toward greater competency in right stance. When musculoskeletal function is not relatively balanced, the left side does not achieve full stance phase of gait or full exhalation phase of respiration, and the right side will likely not achieve effective swing phase of gait or efficient inhalation phase of respiration. The daily repetitive nature of these basic activities of life reinforces and strengthens unbalanced asymmetrical function. Without intervention, the unequal stresses placed on

**Figure 7.** Alternating reciprocal gait viewed from above used with permission from the Postural Restoration Institute®.

musculoskeletal elements will likely progress to structural changes.

of balanced, biomechanical asymmetry [2].

144 Innovations in Spinal Deformities and Postural Disorders

Copyright 2017, www.posturalrestoration.com

The development of muscle compensation follows a predictable pattern based on the model of human right-side dominance. Interventions to restore balance to a dysfunctional system will be maximally effective if the underlying baseline is understood and accounted for in the intervention. To this end, PRI describes muscle patterns based on a right-side dominant model. These patterns identify polyarticular muscle chains within the body, defined as a series of muscles, which overlap one another having fibers in the same direction and spanning multiple joints and thereby working synergistically together [2].

The anterior interior chain (AIC) governs the pelvis, lumbar spine, and lower extremities (see **Figure 8A**). It is so named because it is comprised of muscles located anterior to the spine and situated within the abdominal cavity. Muscles of the AIC are active during swing phase of gait (see **Figure 8B**). Swing phase of gait corresponds to the left nondominant muscle bias. The leftside pattern is, therefore, exemplified by the body's configuration during swing phase of gait.

**Figure 8.** (A) Muscles of the left anterior interior chain. Copyright—3D4 medical modified with permission by the Postural Restoration Institute®. (B) Left anterior, interior chain in left swing phase of gait.

The biomechanical elements are already familiar from earlier description: the lumbar spine, sacrum, and pelvis orient to the right. The left hemipelvis rotates anteriorly, abducts and externally rotates, facilitating muscles that promote left swing through. These AIC muscles include the left diaphragm, the left psoas major, the left iliacus, the left tensor fasciae latae, the left biceps femoris, and the left vastus lateralis. Simultaneously, the left anterior ribcage elevates and externally rotates as the left diaphragm flattens into an inhalation position. The left lumbar spine is pulled forward and downward by the psoas and forward and upward by the diaphragm, resulting in increased lumbar lordosis [3] (see **Figure 4**).

This is the normal swing through configuration. However, when body neutrality is lost, the left AIC pattern remains tonically active. Persistence of the left swing through pattern interferes with full recruitment of its opposite, the muscles of left stance [31]. Consequently, left stance performance is weakened and less stable. Left AIC patterning thereby reinforces rightside dominance that is neurologically encoded as the new normal posture. Biomechanical strategies to compensate for this maladaptive left stance phase often involve overuse of the right lower extremity and/or malpositioning and stress of the left lower extremity joints. The right AIC muscle chain is not constrained by underlying positional insufficiency, and it supports right stance well. However, the efficiency of right swing through may be limited due to left-side instability during left stance as well as due to persistent overactivity of the right adductors and lateral abdominals.

The upper trunk muscle chain described by PRI is named the "Brachial Chain" (BC) (see **Figure 9A**). The BC balances rotational forces generated by the AIC by counterrotating the spine and ribcage to a forward direction. A right BC pattern complements the left AIC pattern by promoting left thoracic rotation (see **Figure 9B**). Counterrotation takes place in the approximate region of T7–9 [1]. The respiratory diaphragm inserts on the inner surfaces of ribs T7–12 and to the anterior aspect of vertebrae L1–3 on the right and L1,2 on the left. In its normal, exhalatory rest position, the dome of the diaphragm is at about T8. Therefore, the trunk could be considered to be the portion of the torso above the diaphragm. This counterrotation of the trunk is accompanied by ipsilateral side bend due to ipsilateral forward arm swing and to ribcage kinematics [39].

**Figure 9.** (A) Muscle of the right brachial chain. Copyright—3D4 medical modified with permission by the Postural Restoration Institute®. (B) Right brachial chain in left swing phase of gait.

Right arm reach is facilitated by this configuration. As the mid and upper trunk turn leftward, opposite to the right rotation of the lumbar spine and pelvis, ribcage kinematics re-form the shape of the ribcage and its muscular attachments. Left trunk rotation results in right ribcage approximation and internal rotation, and left ribcage expansion and external rotation [39]. This configuration encourages airflow from inhalation to the already-expanded left ribcage and lung while decreasing airflow to the right internally rotated approximated side. Muscles of the BC supporting right ribcage internal rotation include the right triangularis sterni, right sternocleidomastoid, right scalenes, right pectoralis minor and right intercostals, and also muscles of the right pharynx and anterior neck.

left lumbar spine is pulled forward and downward by the psoas and forward and upward by

This is the normal swing through configuration. However, when body neutrality is lost, the left AIC pattern remains tonically active. Persistence of the left swing through pattern interferes with full recruitment of its opposite, the muscles of left stance [31]. Consequently, left stance performance is weakened and less stable. Left AIC patterning thereby reinforces rightside dominance that is neurologically encoded as the new normal posture. Biomechanical strategies to compensate for this maladaptive left stance phase often involve overuse of the right lower extremity and/or malpositioning and stress of the left lower extremity joints. The right AIC muscle chain is not constrained by underlying positional insufficiency, and it supports right stance well. However, the efficiency of right swing through may be limited due to left-side instability during left stance as well as due to persistent overactivity of the right

The upper trunk muscle chain described by PRI is named the "Brachial Chain" (BC) (see **Figure 9A**). The BC balances rotational forces generated by the AIC by counterrotating the spine and ribcage to a forward direction. A right BC pattern complements the left AIC pattern by promoting left thoracic rotation (see **Figure 9B**). Counterrotation takes place in the approximate region of T7–9 [1]. The respiratory diaphragm inserts on the inner surfaces of ribs T7–12 and to the anterior aspect of vertebrae L1–3 on the right and L1,2 on the left. In its normal, exhalatory rest position, the dome of the diaphragm is at about T8. Therefore, the trunk could be considered to be the portion of the torso above the diaphragm. This counterrotation of the trunk is accompanied by ipsilateral side bend due to ipsilateral forward arm

**Figure 9.** (A) Muscle of the right brachial chain. Copyright—3D4 medical modified with permission by the Postural

Restoration Institute®. (B) Right brachial chain in left swing phase of gait.

the diaphragm, resulting in increased lumbar lordosis [3] (see **Figure 4**).

adductors and lateral abdominals.

146 Innovations in Spinal Deformities and Postural Disorders

swing and to ribcage kinematics [39].

The "left AIC, right BC" pattern can be understood as the normal configuration of one half of the gait cycle, i.e., right stance. A *right* AIC, *left* BC pattern would reflect the other half of the gait cycle, i.e., left stance (see **Figure 10**). Human physiological asymmetry and right-side dominance predispose the body for greater right competency. Although left-side function will never be as efficient as the right, left stance can achieve near-equal stability with musculoskeletal balance or body neutrality.

**Figure 10.** Right swing phase of gait illustrating the right anterior interior chain and left brachial chain.

This Left AIC, right BC pattern explains the biomechanics predisposing the development of a right thoracic, left lumbar spinal curvature, which describes 90% of curves [5–7] (see **Figure 11A**). The left AIC, right BC pattern underlies all human posture and movement (see **Figure 11B**). While different circumstances may result in different pathological compensations, generating a variety of stresses and/or structural changes, this innate human asymmetrical bias will be present [1–4].

**Figure 11.** (A) Muscles of the left anterior interior chain and right brachial chain. Copyright—3D4 medical modified with permission by the Postural Restoration Institute®. (B) A classic example of a Left AIC, right BC pattern.
