The thoracolumbar fascia is an extensive fascial system in the back that consists of several layers. It surrounds the erector spinae, multifidi, and quadratus lumborum, thus providing support to these muscles when they contract. Increased bulk in these muscles increases tension in the fascia, perhaps contributing the stabilizing function of these muscles.
The aponeurosis of the latissimus dorsi and fibers from the serratus posterior inferior, internal oblique, and transverse abdominis muscles blend together at the lateral raphe of the thoracolumbar fascia, so contraction in these muscles increases tension through the angled fascia, providing stabilizing forces for the lumbar spine.
Muscle Control in the Cervical Spine
The fulcrum of the head on the spine is through the occipital/atlas joints. The center of gravity of the head is anterior to the joint axis and therefore has a flexion moment. The weight of the head is counterbalanced by the cervical extensor muscles (upper trapezius and cervical erector spinae). Tension and fatigue in these muscles, as well as in the levator scapulae (which supports the posture of the scapulae), is experienced by most people who experience postural stress to the head and neck. The position of the mandible and the tension in the muscles of mastication are influenced by the postural relationship between the cervical spine and head.
Mandible.The mandible is movable structure that is maintained in its resting position with the jaw partially closed through action of the mandibular elevators (masseter, temporalis, and internal pterygoid muscles).
Suprahyoid and infrahyoid group. The anterior throat muscles assist with swallowing and balancing the jaw against the muscles of mastication. These muscles also function to flex the neck when rising from the supine position. With a forward head posture, they, along with the longus colli, tend to be stretched and weak so the person lifts the head with the sternocleidomastoid (SCM) muscles.
Rectus capitis anterior and lateralis, longus colli, and longus capitis. The deep craniocervical flexor muscles have segmental attachments and provide dynamic support to the cervical spine and head. The longus colli is important in the action of axial extension (retraction) and works with the SCM for cervical flexion. Without the segmental influence of the longus colli, the SCM would cause increased cervical lordosis when attempting flexion.
Multifidus. With its segmental attachments, the multifidus is thought to have a core stabilizing function in the cervical spine similar to its function in the lumbar region.
Neurological Control: Influence on Stability
The muscles of the neck and trunk are activated and controlled by the nervous system, which is influenced by peripheral and central mechanisms in response to fluctuating forces and activities. Basically, the nervous system coordinates the response of muscles to expected and unexpected forces at the right time and by the right amount by modulating stiffness and movement to match the various imposed forces.
Feedforward control and spinal stability. The central nervous system activates the trunk muscles in anticipation of the load imposed by limb movement to maintain stability in the spine. Research has demonstrated that there are feedforward mechanisms that activate postural responses of all trunk muscles preceding activity in muscles that move the extremities and that anticipatory activation of the transversus abdominis and deep fibers of the multifidus is independent of the direction or speed of the postural disturbance. The more superficial trunk muscles vary in response depending on the direction of arm and leg movement, reflective of their postural guy wire function, which controls displacement of the center of mass when the body changes configuration. There are reported differences in patterns of muscle recruitment in patients with low back pain with delayed recruitment of the transversus abdominis in all movement directions and delayed recruitment of the rectus abdominis, erector spinae, and oblique abdominal muscles specific to the direction of movement compared to healthy subjects.
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