The SCMs are reliable neck flexors when they fire in proper order. However, they serve as poor substitutes for longus capitis due to their insertion at the mastoid process. When reciprocally weakened, longus capitis muscles give way to powerful SCMs which are forced to fire first, causing the head to cock back into extension (not flexion). 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.
When the neck’s usual firing-order sequence is disrupted, synergistic muscles can torsion and compress facet joints, causing chronic degenerative conditions such osteoarthritis, migraines and dowager’s humps. The brain rectifies by layering the area with protective spasm, which perpetuates pain-spasm-pain cycles as the neck’s firing order pattern is further disrupted. Luckily, the trained eye 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.