downward, the cervical spine curves forward, the thoracic spine curves backward, the lumbar spine curves forward again and the sacral spine curves backward again. Together, these four curves provide for resilience and the ability to resist gravity. This minimizes the stress to the vertebral joints, the core (paraspinal) muscles, and the surrounding tissues.

The fundamentals of upright posture require that a plumb line fall through the anatomical center of the body. From the side view, that line would intersect the back of the ear, through the center of the shoulder joint, through the center of the pelvis, and through the center of the ankles.

From the front view, the plumb line should fall through the center of the head, long the spine and right through the center of the sacrum, and land equally placed between the feet (see the diagrams, above).

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Posture in Motion
 

Of all the characteristics of being human, good posture has to do with the effortless ability to be bipedal—stand upright against gravity for long periods. But good posture does not stop there. We also desire to move around in our environment and do things. The ability to put one foot in front of the other and get from place to place requires a constant and pre-programmed updating of all the input that would allow that activity. Greater muscle tone produces greater resistance to stretch and faster response to perturbation.

The functional spine maintains its normal alignment of each vertebra to the next while standing, sitting, and/or lying down, with or without movement. The fundamentals of normal human movement support and encourage the proper relationship of spinal mechanics.
 

In contrast, the dysfunctional spine leads to improper posturing, especially when walking, or standing for long periods. Poor posture puts increased stress on the back causing discomfort and structural damage with an increased tendency to injury. Moreover, according to certain laws of orthopedics and spinal performance, a dysfunctional spine modifies or molds itself—the results of poly-anionic glycosaminoglycans (PAGs) that create arthritis—as a consequence of a person’s lifestyle. For example, sitting for long periods in ergonomically wrong positions makes people more prone to spinal stress and muscle pain from misalignments and joint breakdown.

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Postural flaws can also present with a forward tilt of the hips, an increase in the curve of the lumbar (lower back) spine, and a protruding stomach. This position places stress over both of the hip joints and lower back.

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​​Anti-gravity Muscle Function
 

Anti-gravity muscles move the bones into their compliant and supporting posture. When these muscles do their job, one could stand forever. However, the truth is that these muscles fail. How can you tell when they fail? A misfiring muscle is accompanied by a burning sense in that muscle. The joints often ache and movement is often difficult, slowed, and painful. However, it may be that there are no indications of muscle problems unless the muscles are tested.

 

Muscle testing can reveal the functional nature of those structural supporters. For example, when standing upright in the

neutral posture, all anti-gravity muscles should be functionally facilitated. There are many muscle tests that can be used, but most commonly two basic muscle tests—using the clavicular portion of the pectoralis major (PMC) and the latissimus dorsi (LD)—can give a satisfactory picture.
 

The Static Posture
 

The ability to stand upright stems from many factors, one of which is the positive support phenomenon. It is based on the perception that putting pressure on the feet as with standing from a seated posture turns on the muscles that resist gravity. It causes the muscles of the lower extremities to work together to stabilize the body and to support its weight.
Watch people as they stand. Check a friend. See the level of the base of their skull as it sits on the neck. Is it level, high on one side, or low on the other?
 

Next check the level of their shoulders. Is one shoulder held higher than the other? Are the shoulder blades level? Does the inside edge of the shoulder blades flare in whole or in part?
 

Check for any tension on one side of the spine relative to the other. The area immediately lateral to the spine is all muscle. Any tension on one side compared to the other can mean that the spinal joints are not moving symmetrically through that area. That can set up hemisphericity that contributes to this structural dysfunction.
 

Look at the highest part of the hips on each side. Is one hip held higher than the other? Place your thumbs on the hipbone—the posterior superior iliac spine, or PSIS—on either side and ask the patient to slowly lift one knee toward their chest, then the other one. The right response is for the hipbone on the side being tested to rise a bit relative to the hipbone on the other side (i.e., Trendelenburg’s test). If the PSIS on the side of the raised leg drops instead of rises, this is an indication of hip joint instability. As a result, you should also check their ankles and feet.
 

The ankles and feet must bear weight properly; they are the whole body’s structural foundation. Any flat-footedness can contribute to postural problems and the further breakdown of the anti-gravity muscles that make up the lower extremities like firm but compliant pillars. Recall what was stated earlier that foot or toe compromise can lead to ankle, knee, and hip involvement.

The Abnormal Posture
 

Abnormal posturing is different from "bad posture" or "slouching.” An abnormal posture is a deliberate or reflexive tendency to hold a particular body position, or to move one or more parts of the body in a particular way.
Certain abnormal posturing behaviors may indicate specific lesions to the nervous system. It could be a sign of some local involvement or it might be a more serious sign of central nervous system damage. However, there are other common causes of abnormal posturing—soft signs—nonetheless central nervous system lesions.

Normally, when a muscle contracts, the muscles on the opposite side of that joint provide some resistance to contraction to maintain stability. That is a type of posturing, too. Abnormal posturing occurs when damage to the central nervous system (brain and/or spinal cord) results in complete or partial lack of opposition to muscle contraction in various muscle groups.
While abnormal posturing is often observed as an involuntary flexion or extension of the arms and/or legs indicating severe brain injury, it also displays in more functional situations. The hard signs of abnormal posturing occur when one set of muscles becomes hampered while the opposing set is enabled, and an external stimulus such as pain causes the working set of muscles to contract. The posturing may also occur without a stimulus. The hard signs of abnormal posturing are an important indicator of the amount of damage that has occurred to the brain, and are one key to the severity of comatose states in both adults and children.

Soft postural signs can display much the same way as do hard postural signs, but without the pathology of frank tissue damage. The soft postural signs are functional, responding to dynamic processing problems in the central nervous system, but they can often be corrected with certain manipulative therapies.

Summary

Upright posture is one of several uniquely human traits. The bipedal posture allows humans to move about and interact with their environment. It only makes sense that that movement should be symmetrical and reciprocal, and accompanied by balance. However, as a result of inappropriate sensory input, the functional posture can easily lose its stability, and that is when joint and muscle problems develop leading to various types of aches and pains, and an increased potential for injury. Structural compromise also involves organ function, especially the eyes and ears, and the ability to remain upright in one’s own environment.