A Different Chemical Environment Near Trigger Points

Using fine microdialysis needles, researchers have directly sampled the tissue fluid surrounding active myofascial trigger points and found significantly elevated concentrations of substance P, calcitonin gene-related peptide (CGRP), bradykinin, and inflammatory cytokines compared to both non-tender muscle and distant control sites (Shah & Gilliams, 2008). This "biochemical milieu" is thought to sensitise local nociceptors, contributing to the spontaneous tenderness characteristic of an active trigger point.

Engaging a Spinal Reflex

Mechanically disrupting a taut band of muscle fibre with a needle can elicit a local twitch response — an involuntary, brief contraction of the muscle fibres mediated by a spinal cord reflex arc, rather than a voluntary or centrally-initiated movement (Hong, 1994). Needling is also thought to normalise the abnormal electrical activity recorded at dysfunctional motor endplates, a key feature of the integrated hypothesis of trigger point formation (Gerwin et al., 2004).

Effects Beyond the Needle Site

Dry needling's effects are not limited to the local tissue. Needling can engage the same descending pain-inhibitory pathways activated by other forms of manual therapy, and segmental and even generalised changes in pain sensitivity have been recorded following treatment of a single trigger point — evidence that the nervous system, not merely the local muscle fibre, is a genuine target of the intervention.

References & Further Reading

  1. Shah JP, Gilliams EA. Uncovering the biochemical milieu of myofascial trigger points using in vivo microdialysis: an application of muscle pain concepts to myofascial pain syndrome. J Bodyw Mov Ther. 2008;12(4):371-384.
  2. Hong CZ. Lidocaine injection versus dry needling to myofascial trigger point: the importance of the local twitch response. Am J Phys Med Rehabil. 1994;73(4):256-263.
  3. Gerwin RD, Dommerholt J, Shah JP. An expansion of Simons' integrated hypothesis of trigger point formation. Curr Pain Headache Rep. 2004;8(6):468-475.