"The human body is not symmetrical. The neurological, respiratory, circulatory, muscular and vision systems are not the same on the left side of the body as they are on the right, and vice versa. They have different responsibilities, function, position and demands on them. This system asymmetry is a good thing and an amazing design. The human body is balanced through the integration of system imbalances. The torso, for example, is balanced with a liver on the right and a heart on the left. Extremity dominance is balanced through reciprocal function; i.e. left arm moves with right leg and vice versa.

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Postural Restoration Institute® (PRI) credentialed professionals recognize these imbalances and typical patterns associated with system disuse or weakness that develops because of dominant overuse. This dominant overuse of one side of the body can develop from other system unilateral overuse. For example, if the left smaller diaphragm is not held accountable for respiration as the right is, the body can become twisted. The right diaphragm is always in a better position for respiration, because of the liver’s structural support of the right larger diaphragm leaflet. Therefore, the left abdominals are always important to use during reciprocal function, such as walking, to keep the torso balanced.

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Keeping the right chest opened during breathing is also challenging since there is no heart muscle inside the right side of the chest. Standing mainly on the right lower extremity to offset the weight of the left upper torso, assists in moving the pelvis forward on the left and the shoulder complex down on the right. This asymmetry compliments the special functions of the two sides of the brain. Although the two sides (hemispheres) of the brain share responsibilities for some functions, each hemisphere has its own “specialties”. Each hemisphere controls the opposite side of the body. The left brain has more responsibilities for speech and language and thus the right upper extremity becomes a dominant extremity in communication, growth and development. PRI credentialed professionals recognize when this normal pattern is not balanced sufficiently with left extremity neurologic and muscular activity.

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When these normal imbalances are not regulated by reciprocal function during walking, breathing or turning, a strong pattern emerges creating structural weaknesses, instabilities, and musculo-skeletal pain syndromes. Balancing muscle activity around the sacrum (pelvis), the sternum (thorax) and the sphenoid (middle of the head) through a PRI approach best positions multiple systems of the human body for appropriate integrated asymmetrical function. PRI credentialed professionals incorporate reciprocal function to reduce ‘leading’ with the left pelvis and right arm, and respiratory function to maximize airflow in and out of the right lung.

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Vision, occlusion, hearing, foot pressure, occupational demands, in-uterine position, etc. can all influence asymmetrical tendencies and patterns. Humpback whales bottom-feed on their right side, lemurs tend to be lefties when it comes to grabbing their grub, toads use their right forepaw more than their left, chimpanzees hold a branch up with the left hand and pick the fruit with their right hand, and humans usually balance their center of gravity over their right leg for functional ease and postural security. PRI credentialed professionals recognize the more common integrated patterns of human stance, extremity use, respiratory function, vestibular imbalance, mandibular orientation and foot dynamics; and balance these patterns, as much as possible, through specific exercise programs that integrate correct respiration with left side or right side inhibitory or faciliatory function."

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Quoted directly from www.posturalrestoration.com