In this open, uncontrolled trial, 20 patients with upper trapezius muscle trigger point pain and ipsilateral masseter muscle pain received a single trigger point injection of 2% lidocaine solution ...

It may be related to excessive accumulation and release of acetylcholine (a neurotransmitter ... trauma to the muscle helps to create a “trigger point" (tight lump or knot in the muscle).

Active MTrPs were found in the infraspinatus muscle in 56 subjects and in the upper trapezius muscle in 42 subjects. In addition, active MTrPs were highly prevalent in the middle trapezius (n = 31 ...