Trigger points or trigger sites are described as hyperirritable spots in skeletal muscle that are associated with palpable nodules in taut bands of muscle fibers. Trigger point practitioners believe that palpable nodules are small contraction knots[ambiguous] and a common cause of pain. Compression of a trigger point may elicit local tenderness, referred pain, or local twitch response. The local twitch response is not the same as a muscle spasm. This is because a muscle spasm refers to the entire muscle contracting whereas the local twitch response also refers to the entire muscle but only involves a small twitch, no contraction.
The trigger point model states that unexplained pain frequently radiates from these points of local tenderness to broader areas, sometimes distant from the trigger point itself. Practitioners claim to have identified reliable referred pain patterns, allowing practitioners to associate pain in one location with trigger points elsewhere. Many practitioners of chiropractic and massage therapy find the model useful, but the medical community at large has not embraced trigger point therapy. There is no consistent methodology for diagnosis of trigger points and a dearth of theory to explain how they arise and why they produce specific patterns of referred pain。