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Jeffrey P. Okeson


Local twitch responses (LTRs) can be elicited by snapping palpation of myofascial trigger points (TrP) or TrP injections. Objective: To characterize the LTR elicited by TrP injection and snapping palpation on surface electromyography (sEMG) in subjects with myofascial pain in 14 female subjects. Methods: Surface EMG electrodes were placed around the TrP and a control site on the trapezius muscle. Then the following protocol was carried out: tension and contraction of the ipsilateral trapezius muscle, baseline resting activity (five minutes), snapping palpation of the TrP and the control sites, TrP injection, and final resting activity (five minutes). The following data were recorded: pain ratings, areas of referred pain, presence of LTR, and sEMG recordings. Results: During the TrP injection, the investigator found LTRs in only 36% of the subjects, while 64% of the subjects reported that they felt the LTR, and the sEMG recorded only one LTR in one subject. Despite the low percentage of LTRs elicited clinically (36%), a large number of subjects (71%) reported more than 50% immediate reduction in pain intensity after the TrP injection. Conclusion: The sEMG is unable to register the LTR elicited by snapping palpation and TrP injection.