Inability of surface electromyography to register the local twitch response elicited by trigger point injection and snapping palpation in myofascial pain patients

Objectives: This study aimed to characterize the local twitch responses [LTR] elicited by trigger point [TrP] injection and snapping palpation. Methods: The LTR was recorded with surface electromyography [sEMG] electrodes placed at the TrP and a control site on the trapezius muscle in 16 female subjects with myofascial pain. The following protocol was carried out: tension and contraction of the ipsilateral trapezius muscle, baseline resting activity, snapping palpation of the TrP and the control sites, TrP injection, and final resting activity. Results: During the TrP injection, the investigator found LTRs in 31 percent of the subjects, while 63 percent of the subjects reported that they felt the LTR, and the sEMG recorded only one LTR in one subject. Conclusions: The sEMG was unable to register the LTR.