**2. Fundamental PRI concepts**

The following fundamental concepts provide a new perspective on effective restorative techniques for treating scoliosis, other spinal dysfunctions, and postural disorders. The concepts explain the PRI baseline model of innate human asymmetry. Each is discussed in detail in this chapter: (1) human asymmetry arises from our innate anatomy and physiology and exerts significant influence on human posture and movement. (2) Ideal or neutral posture results from relative musculoskeletal balance of our asymmetrically organized body. (3) Anatomical and physiological asymmetries evident in the respiratory system are powerful contributors to our biomechanical function. (4) Right-side dominance is the functional result of physiological asymmetry. (5) The movement of the respiratory diaphragm and the pelvic diaphragm (pelvic floor muscles) is synchronized during breathing. The pelvis is a primary structure that facilitates gait. The synergistic activity of these two diaphragms links respiration and gait. (6) Gait requires integrated muscle activity, different on two sides of the body, in order to stay erect on one leg as the other advances the body through space. In the context of human asymmetry, right-side stance phase and left-side swing phase will be most competent. (7) Biomechanical dysfunction begins in the sagittal plane.

#### **2.1. Innate physiological human asymmetry**

**1. Introduction**

136 Innovations in Spinal Deformities and Postural Disorders

sate for the imbalance.

**2. Fundamental PRI concepts**

Recognition of inherent physiological asymmetry has not yet been applied to the understanding, assessment, or treatment of scoliosis or other spinal and postural disorders. Even without an accurate baseline model of human form and function, interventions to correct dysfunction can be successful; however, while a local dysfunction may be rectified, the underlying biomechanical imbalance will persist as will the musculoskeletal strategies developed to compen-

The Postural Restoration Institute® (PRI) methodology is a theoretical framework, which describes a model of universal human anatomical and physiological asymmetry. This unique model provides a new baseline for understanding common postures, movement patterns, and respiratory mechanics, which generate from our asymmetrical bias. It also explains the factors that support human right-side dominance. While human asymmetry can be understood as a positive factor that facilitates movement, overuse or misuse of the dominant muscle pattern will promote progressive imbalance within the body and will likely result in dysfunction. The treatment goal for dysfunction resulting from musculoskeletal imbalance needs to be restoration of the baseline in which there is relative balance between the dominant and nondominant muscle patterns [1–4]. Scoliosis is an example of a tri-planar, biomechanical dysfunction. In its most common form (90% of the cases), right thoracic convexity and left lumbar convexity [5–7], it exemplifies the extreme progression of normal human asymmetry according to the PRI model, which will be described in this chapter. Other postural disorders such as kyphosis and lordosis, exhibiting primary sagittal plane dysfunction, also belong to the spectrum of disorders developing from unbalanced human asymmetry. These conditions result in musculoskeletal stress, subsequent structural damage, loss of efficiency in movement and in respiratory function, as well as in a diminished quality of life. This chapter introduces the fundamental concepts of PRI's theoretical framework and its baseline model. It will then describe how PRI's clinical tests can more accurately evaluate a patient's status by taking into account the inherent human asymmetry. These tests guide exercise prescription and treatment progression. Some examples of exercises used in the treatment of scoliosis have been selected to demonstrate activity progression from supported target muscle isolation, to complex, unsupported, multiple muscle integration, all with a major emphasis on respiration. Three case studies are presented here to illustrate this process. Many similarities exist between PRI rehabilitation concepts and exercises and the well-known Schroth methodology [8, 9].

The following fundamental concepts provide a new perspective on effective restorative techniques for treating scoliosis, other spinal dysfunctions, and postural disorders. The concepts explain the PRI baseline model of innate human asymmetry. Each is discussed in detail in this chapter: (1) human asymmetry arises from our innate anatomy and physiology and exerts significant influence on human posture and movement. (2) Ideal or neutral posture results from relative musculoskeletal balance of our asymmetrically organized body. (3) Anatomical and physiological asymmetries evident in the respiratory system are powerful contributors to Studies of many aspects of human asymmetry abound in the literature [10–15]. Much of this fascinating material is beyond the scope of this chapter. However, asymmetries of the internal organization of the body, organ weight distribution, muscle mass, and muscle attachments are all factors that contribute significantly to human asymmetrical posture and movement patterns. For example, the heart and its vessels share the left upper quadrant with two lobes of the lung. The right upper quadrant is less full, housing three lung lobes. The weight of the heart is offset by the large, heavy liver, which sits—lower than the heart—in the right lower quadrant [14]. This weight distribution and placement difference facilitates a gravitational shift of the body onto the right lower extremity, thereby promoting right stance. The left lower quadrant is less weighty because of the small spleen and usually empty stomach [1–4] (see **Figure 1**).

**Figure 1.** Asymmetrical organ distribution. Scottff72 copyright 123RF.com

The upper and lower quadrants are separated by the respiratory diaphragm, a unique muscle that spans the internal dimension of the body. The diaphragm is comprised of a stronger, larger, and better-supported right leaflet, and a smaller, less efficient, left leaflet. The diaphragm's respiratory mechanics exert a powerful asymmetrical influence on the torso. The crura of the right leaflet, which inserts onto three lumbar vertebrae L1–3, is also stronger and thicker than the left crura, which inserts on only two lumbar vertebrae L1, 2 [16] (see **Figure 2**). This distribution exerts a right rotational influence on the lumbar spine, orienting it to the right. Articulation of the lumbar spine with the sacrum orients the sacrum to the right. Strong ligaments bonding the sacrum to the pelvis effect right rotation of the pelvis as well. This right rotational orientation of the lower spine and pelvis is enhanced by the gravitational shift of the body over the right leg due to the weight of the liver on the right side of the body [1–4].

**Figure 2.** Diaphragm with crura. Florida Center for Instructional Technology copyright 2004–2017.

Asymmetry facilitates movement. In a balanced system, asymmetry is a positive, vitalizing force. In the human body, loss of balanced musculoskeletal function precipitates and reinforces overuse of dominant postures and patterns because of the underlying structural bias toward right stance, influenced by organ placement, weight distribution, and muscle attachment. Habit and repetition perpetuate and reinforce dysfunction. Innate physiological human asymmetry may well be a factor in the onset and development of scoliosis and other postural disorders.

#### **2.2. Neutral posture reflects relative musculoskeletal balance**

Webster's New World Medical Dictionary defines "neutral posture" as the stance that is attained when the "joints are not bent and the spine is aligned and not twisted" [17]. Neutral posture gives rise to the concept of "ideal posture" in which the alignment of body segments involves a minimal amount of stress and strain and which is conducive to maximal efficiency in use of the body [18, 19]. Ideal posture is critical for proper respiratory action [20]. When the body is in its ideal or neutral alignment, diaphragmatic respiratory mechanics are optimized [16].

Due to physiological asymmetry, a neutral posture does not imply strict symmetry; rather, it describes a position of relative structural balance and a readiness for movement in any direction. Loss of relative musculoskeletal balance reflects persistence of a structural bias resulting from habitual, repetitive muscle activity. For example, hyper lumbar lordosis is a frequently seen, sagittal plane, postural disorder. Positional alignment of the ribcage and pelvis has become imbalanced. The lumbar paraspinals have shortened and tightened, and the abdominal muscles have become overlengthened and weak [19, 21]. Neither of these muscle groups exists in their neutral or rest position. The neutral position of a muscle is equivalent to physiological rest [19]. With hyper lumbar lordosis, all future movements will initiate from this unbalanced basis of the skeleton (ribcage and pelvis) now supported and reinforced by adaptive muscle imbalance. Movement into any direction will require compensation by other muscles or will not be accomplished. Compensatory muscle activity is less efficient, energy demands increase, and stress accumulates on poorly aligned joints. Restoration of musculoskeletal balance would address these multiple issues [1–4].

Respiration is a key component of posture [22–27]. Our ability to breathe efficiently affects all aspects of our daily function and our endurance for activity. Through its anatomic attachments, the position and functional efficiency of the respiratory diaphragm is highly dependent on musculoskeletal posture as well as on tonic muscular activity [23]. The average person takes 21,000 breaths per day [28] with the respiratory diaphragm as a key muscle of respiration [22, 25]. Thus, the respiratory pattern is powerful in its contributions to posture. Efficient respiratory mechanics are dependent on neutral body position and muscle function [16].

When the diaphragm is compromised, it not only causes inefficient breathing patterns but also becomes a key contributor to the persistence and progression of postural disorders, including hyper lumbar lordosis, [29] kyphosis, forward head posture [20], and changes in ribcage symmetry [9, 16] as seen in scoliosis.
