ASC, b. gen topic Upper Cervical Discussion 16a. I think this muscular contraction is reflexive, and due to nociceptive input. An upper cervical subluxation is no different than any other with this, albiet big, exception. Generally, upper cervical practitioners look for these distortions as a pre-text to adjust the patient. Without these signs, most do not adjust.
Some research says yes, but the jury is still out.
The implications of postural distortion on a patient are not difficult to imagine. The tangible benefit is getting rid of this distortion. This causes the joint to be moved into positions that, prior to injury, it would not go. Adjustment re-sets the joint and reflexes back to normal, but there is some permanent loss of kinesthetic sensitivity. The atlas direction and degree of misalignment are very similar to what was noted before.