Part Two: Bringing the Body Back into Balance
by Erik Dalton, PhD
Often seen as a structurally subtle body segment, the neck is burdened with the challenging task of supporting and moving the human head. Because of the tension, trauma and poor postural habits inherent in today’s workplace, it is no surprise that head-on-neck and neck-on-thorax disorders rank high among the most common pain generators driving people into bodywork practices.
This two-part series is excerpted from the author’s new textbook, Advanced Myoskeletal Techniques. Part One examined the causes, conditions and corrections for one of the most prevalent and painful of all structural disorders: forward-head postures. In this issue, common neck pathologies will be reviewed with special focus on the age-old “straight-neck” controversy and related conditions such as osteoarthritis, TMJ dysfiinction and Dowager’s hump.
The physiology of muscle imbalance
In the early 1900s, Sir Charles Scott Sherrington, an English physiologist and Nobel Prize recipient, first described the neurological concept of reciprocal innervation1 Simply stated, if a muscle receives a nerve impulse to contract, its antagonist simultaneously receives a nerve impulse to relax. Sherrington’s Law of Reciprocal Inhibition further describes how one muscle group neurologically weakens when length-tension imbalance occurs to paired antagonists; i.e., tight pectorals overpowering and reciprocally weakening rhomboid major and lower trapezius. But why do these substitution patterns develop? Altered length-tension imbalance patterns typically result from faulty posture, gravitational stress, repetitive movement, cumulative trauma, and loss of neuromuscular control.
Synergistic dominance Synergistic may be defined as “acting together; enhancing the effect of another force.” Therefore, if muscles perform the same task at a particular joint, they are termed synergistic. Synergistic dominance occurs as “helper” muscles are recruited to take over function when a “prime mover” muscle fails, much like when a football coach calls in the substitute players when a key player is injured. Synergistic stabilizers are designed to help but not be primary contributors to a particular movement.
Reciprocal inhibition is often the precursor to synergistic dominance. For example, in forward-head postures, the client’s suboccipitals are often maintained in a hypercontracted state as they battle gravity to keep the eyes level with the horizon. As the head cocks back and moves forward on the neck, the antagonist longus capitis muscles—which bind the anterior surface of the upper cervical vertebrae to the occipital base become overstretched and weak. Sensing the longus capitis muscles can no longer carry out their duty as primary head-on-neck flexors, the brain calls on the powerful sternocleidomastoids (SCMs) as pinch-hitters.
The SCMs are reliable neck flexors when allowed to fire in proper order. However, they serve as poor subs for longus capitis due to their insertion at the mastoid process. When reciprocally weakened longus capitis muscles give out, the powerful SCMs are forced to fire first, causing the head to cock back into extension (not flexion). Although the suboccipitals appreciate added hyperextension support from the SCMs, neural and vascular structures embedded at the posterior O-A joint aren’t so happy with the excessive compression. Therapists may choose from several strategies to unwind this common head-on-neck imbalance pattern. Two approaches for releasing tight suboccipitals and SCMs are demonstrated in Figures 1 and 2. The “chin-tucking” exercise shown in Figure 3 helps tonify weak deep-neck flexors.
When the neck’s normal firing-order sequence is disrupted, synergistic muscles can torsion and compress facet joints, causing chronic degenerative conditions such osteoarthritis, migraines and Dowager’s hump. The brain compensates by layering the area with protective muscle spasm, which perpetuates pain-spasm-pain cycles as the neck’s firing order pattern is further disrupted. Fortunately, the trained eye of structurally-trained pain-management therapists can usually spot synergistic dominance patterns. The client’s gait may reveal certain body parts that appear frozen in time, as chronically embedded compensations have caused the brain to sacrifice complexity of movement for stability. Fortunately, simple tests help determine if synergistic dominance exists at a particular joint.