There is anatomical terminology in this one hope the basics make sense to everyone though.
Atlas Subluxation Affects on Muscles
From Dr Marshall Dickholtz, D.C. and NUCCA
A stressor has been defined as a condition in the body produced by an injurious factor and manifested by a syndrome (H.Selye). A subluxated C1 distorts the spine and the pelvis because it causes spastic contracture of the extensor (antigravity) muscle of the spinal column. Spinal and bodily distortion result. A subluxated C1- therefore, is acting as an injurious factor, manifesting itself as a syndrome, which is verifiable by measurement and can be correlated to the C1 subluxation. The patient with a subluxated C1 has a subluxated spinal column, an over-innervation of the motor neurons of the spinal cord, neuromuscular imbalance, loss of muscular synergism, distortion of the spinal column from the true axis of the body, and leg disparity. This is the C1 subluxation complex syndrome, and is correctable solely from a precise and predetermined C1 adjustment.
If disequalibrium and cervical spine displacement do not cause a state of subluxation until C1 moves laterally on the occipital condyles, what constitutes a normal lateral range of motion for C1? Vertebrae can be shown to displace and not cause detriment or insult to the nervous structure. If a vertebrae does displace and thereby causes insult to the nervous structure, it is logical to assume that it has abnormally moved, or moved beyond its normal range of motion. Because C1 cannot misalign laterally more than one half of a degree from its alignment to the occipital condyles (about the thickness of a sharp pencil mark), without imbalancing the neurological inhibitory mechanism of the reticular formation at the caudal end of the brain stem. C1 has practically no normal lateral range of motion.
This phenomenon has been observed and tested on over 10,900 cases over a period of many years. The C1 distortion syndrome has always manifested itself whenever C1 has moved laterally three-quarters of one degree or beyond on the occipital condyles when the vertebra was moving from its normal position toward the abnormal position.
The type of neurological detriment that is caused by the lateral displacement of C1 on the occipital condyles appears to be a mechanical tractionization of the caudal end of the brain stem. It has been noted in medical literature that pathological and traumatic situations affecting the brain stem can produce impairment or loss of the inhibitory control over the body's extensor musculature. National Upper Cervical Chiropractic Research Association (NUCCA) research on the effects of a subluxated C1 on the caudal end of the brain stem confirms the medical hypothesis.