<P> Trigger points form only in muscles . They form as a local contraction in a small number of muscle fibers in a larger muscle or muscle bundle . These in turn can pull on tendons and ligaments associated with the muscle and can cause pain deep within a joint where there are no muscles . The integrated hypothesis theory states that trigger points form from excessive release of acetylcholine which produces sustained depolarization of muscle fibers . Indeed , the trigger point has an abnormal biochemical composition with elevated concentrations of acetylcholine , noradrenaline and serotonin and a lower pH . These sustained contractions of muscle sarcomeres compresses local blood supply restricting the energy needs of the local region . This crisis of energy produces sensitizing substances that interact with some nociceptive ( pain ) nerves traversing in the local region which in turn can produce localized pain within the muscle at the neuromuscular junction ( Travell and Simons 1999 ) . When trigger points are present in muscles there is often pain and weakness in the associated structures . These pain patterns in muscles follow specific nerve pathways and have been readily mapped to allow for identification of the causative pain factor . Many trigger points have pain patterns that overlap , and some create reciprocal cyclic relationships that need to be treated extensively to remove them . </P>
where are trigger points located in the body
muscles