08/13/2025
The reduction of pain and disability from spinal manipulation is well recognized and clinically documented. Gillette suggests that spinal adjustments may initiate both a short-lived phasic response triggered by stimulation of superficial and deep mechanoreceptors, and a longer-lived tonic response triggered by noxious-level stimulation of nociceptive receptors. The phasic response is hypothesized to initiate a local gating effect, but pain inhibition terminates with cessation of therapy. The tonic reponse initiated by noxious levels of mechanical stimulation is more powerful and capable of outlasting the duration of applied therapy.
Adjustments that induce joint cavitation and capsular distraction may be a source of nociceptive stimulation capable of initiating relatively long-lasting pain inhibition. This concept supports the premise that the slight discomfort that may be associated with adjustments is causally associated with a positive therapeutic effect.
The potential for spinal adjustments to act directly on the pain system opens up the possibility that manipulation may have the ability to diminish persistent pain that is neuropathic in origin. Chronic neuropathic pain may result from plastic changes and central sensitization of the nervous system. Central sensitization refers to plastic changes in the nervous system that result from persistent amplification of nociceptive synaptic transmission. This can result in the persistence of pain states even after the offending peripenial pathologic injury and inflammation have resolved.
The short-term burst of proprioceptive and nociceptive input associated with adjustments, much like transcutaneous electrical nerve stimulation and acupuncture, have also been theorized to increase the levels of neurochemical pain inhibitors. Both a local release of enkephalins, initiated by stimulation of the neurons of substantia gelatinosa, and a systemic increase in plasma and cerebrospinal fluid endorphin levels, initiated by stimulation of the hypothalamic pituitary axis, have been proposed. Both substances act as endogenous opioid pain inhibitors and may play a role in the analgesic effects of adjustments...
~ Chiropractic Technique (Third Edition)- Principles and Procedures
( Thomas F. Bergmann, David H. Peterson).