Mechanism #1: Extra-segmental Analgesia
In 1974 it was proven that acupuncture increases pain threshold. This was performed through a process called Neuromodulation.1 Neuromodulators are opioid peptides. Four of them have been confirmed to release during an acupuncture treatment.2 One in particular, beta-endorphin, plays an important role in acupuncture analgesia. Studies show that beta-endorphin is released in pain patients receiving acupuncture, whereas a control group had no increased numbers of this neuromodulator. 3
Mechanism #2: Central Regulatory
Acupuncture also stimulates deeper parts of the brain, e.g. the limbic system. 4,5 Many of the ways we perceive and respond to pain is the responsibility of the limbic system. Perhaps this is why "sham acupuncture" has some therapeutic affect and can possibly cause confusion during research.
Mechanism #3: Local Affects
Two decades ago, it was determined that a neuropeptide called calcitonin gene related peptide (CGRP) is released at the needle insertion site. CGRP causes vasodilation and increases blood flow to the affected local injured tissues. This helps speed up the healing process.
Mechanism #4: Segmental Analgesia
As we know, pain signals travel via unmyelinated C fibers to the spinal segment and go through the dorsal horn. This is known as the pain or nociceptive pathway. When performing acupuncture near the site of pain or an area innervated by the same spinal segment, we are able to block those pain signals traveling to the dorsal horn. How? Acupuncture stimulates alpha delta fibers which have been shown to decrease the activity in the dorsal horn.6
Mechanism #5: Myofascial Trigger Point Release
Most trigger points develop due to injury (acute or repetitive stress) and tend to develop around the area that is affected. Trigger points have more electrical activity (detected by EMG7) which, in turn, causes a release in acetylcholine (ACh). It is the presence of ACh that leads the endplates of a muscle fiber to inhibit the calcium pump. This depolarizes in an uncoordinated way and leads to local contraction of the sarcomeres in the area. As a result, the muscle will shorten.8 By needling the trigger point, it physically disrupts the dysfunctional muscle and causes vasodilation of the area which helps the tissues to heal.
1. Han J. Acupuncture and Endorphins. Neuroscience Letters, 2004 May 6; 361(1-3):258-261.
2. Han J, Terenius L. Neurochemical basis of acupuncture analgesia. Annual review of Pharmacology and Toxicology, 1982;22:193-220.
3. Clement-Jones V, et al. Increased beta-endorphin but not met-enkeph-alin levels in human cerebrospinal fluid after acupuncture for recurrent pain. Lancet, 1980 Nov 1;2(8201):946-949.
4. Hui K, Liu J, et al. Acupuncture modulates the limbic system and subcortical grey structures of the human brain: Evidence from fMRI studies in normal subjects. Human Brain Mapp, 2000;9(1):13-25.
5. Hui K, Liu J, et al. The integrated response of the human cerebro-cerebellar and limbic systems to acupuncture stimulation at ST 36 as evidenced by fMRI. Neuroimage, 2005 Sept;27(3):479-496
6. Sandkuhler J. Learning and memory in pain pathways. Pain, 2000 Nov;88(2):113-118.
7. Hubbard D, Berkoff G. Myofascial trigger points show EMG activity. Spine, 1993 Oct 1;18(13):1803-1807.
8. Mense S, Simons D. Muscle Pain: Understanding Its Nature, Diagnosis and Treatment. Philadelphia: Lippincott Williams, & Wilkins, 1999.