Effect of Mechanical Stress

The ligaments, facet capsules, periosteum of the vertebrae, muscles, anterior dura mater, dural sleeves, epidural areolar adipose tissue, and walls of blood vessels are innervated and responsive to nociceptive stimuli. Mechanical stress to pain-sensitive structures, such as sustained stretch to ligaments or joint capsules or compression of blood vessels, causes distention or compression of the nerve endings, which leads to the experience of pain. This type of stimulus occurs in the absence of an inflammatory reaction. It is not a pathological problem but a mechanical one because signs of acute inflammation with constant pain are not present. Relieving the stress to the pain-sensitive structure relieves the pain stimulus, and the person no longer experiences pain. If the mechanical stresses exceed the supporting capabilities of the tissues, breakdown ensues. If it occurs without adequate healing, musculoskeletal disorders or overuse syndromes with inflammation and pain affect function without an apparent injury. Relieving the mechanical stress (i.e., correcting the posture) along with decreasing the inflammation is important.

Effect of Impaired Postural Support from Trunk Muscles
Little muscle activity is required to maintain upright posture; but with total relaxation of muscles, the spinal curves become exaggerated, and passive structural support is called on to maintain the posture. When there is continued end-range loading, strain occurs with creep and fluid redistribution in the supporting tissues, making them vulnerable to injury.

Continual exaggeration of the curves leads to postural impairment and muscle strength and flexibility imbalances as well as other soft tissue restrictions or hypermobility. Muscles that are habitually kept in a stretched position tend to test weaker because of a shift in the length-tension curve; this is known as stretch weakness. Muscles kept in a habitually shortened position tend to lose their elasticity. These muscles test strong only in the shortened position but become weak as they are lengthened. This is known as tight weakness.

Effect of Impaired Muscle Endurance

Endurance in muscles is necessary to maintain postural control. Sustained postures require continual, small adaptations in the stabilizing muscles to support the trunk against fluctuating forces. Large repetitive motions also require muscles to respond so as to control the activity. In either case, as the muscles fatigue, the mechanics of performance change and the load is shifted to the inert tissues supporting the spine at the end ranges. As described above, with poor muscular support and a sustained load on the inert supporting tissues, creep and distention occur, causing mechanical stress. In addition, injuries occur more frequently after a lot of repetitive activity or long periods of work and play when there is muscle fatigue.

Pain Syndromes Related to Impaired Posture / Postural Fault and the Postural Pain Syndrome

A postural fault is a posture that deviates from normal alignment but has no structural limitations. Postural pain syndrome refers to the pain that results from mechanical stress when a person maintains a faulty posture for a prolonged period; the pain is usually relieved with activity. There are no abnormalities in muscle strength or flexibility; but if the faulty posture continues, strength and flexibility imbalances eventually develop.

Postural Dysfunction

Postural dysfunction differs from the postural pain syndrome in that adaptive shortening of soft tissues and muscle weakness are involved. The cause may be prolonged poor postural habits, or it may be a result of contractures and adhesions formed during the healing of tissues after trauma or surgery. Stress to the shortened structures causes pain. In addition, strength and flexibility imbalances may predispose the area to injury or overuse syndromes that a normal musculoskeletal system could sustain.

Postural Habits

Good postural habits in the adult are necessary to avoid postural pain syndromes and postural dysfunction. Also, careful follow-up in terms of flexibility and posture training exercises is important after trauma or surgery to prevent impairments from contractures and adhesions. In the child, good postural habits are important to avoid abnormal stresses on growing bones and adaptive changes in muscle and soft tissue.

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