A Comparison Study between Electrical Muscle Stimulation and Transcutaneous Electrical Nerve Stimulation on Treatment of Myofascial Pain Syndrome

Background: Myofascial pain syndrome (MPS) originates from myofascial trigger points (MTPs)– hypersensitive nodules commonly found in the trapezius muscle (TM) that cause pain and functional limitations. While transcutaneous electrical nerve stimulation (TENS) is a conventional treatment, a novel approach combining electrical muscle stimulation (EMS) with active stretching (AS) has recently been developed (EMS + AS). Methods: EMS electrodes were placed transversely across muscle fibers to induce localized contractions and thus greater stretch of MTP-containing regions compared to AS alone. EMS plays a role similar to a therapist's hand in passive stretching in that it provides resistance force. Forty-one participants with MTPs in the TM received single sessions of EMS + AS, sham stimulation (SS) + AS, and TENS. Each session included three 10-s stimulations with 10-s rest intervals. Pain intensity (PI), pressure pain threshold (PPT), and surface electromyography (sEMG) for maximal voluntary contraction (%MVC) amplitude analysis of TM function improvement were the three outcome measures used to assess treatment effectiveness. To evaluate the immediate effects of short-duration treatments with EMS + AS compared to SS + AS and TENS. All three treatments were applied in a randomized order. Results: EMS + AS showed significant improvements in PI and PPT (t ₍₄₀₎ = −6.01 and t ₍₄₀₎ = 5.38, p < 0.001, respectively). EMS + AS showed a small sEMG activity during TM function improvement of 0.49 ± 0.056 %MVC at post-treatment, normalized to pre-treatment values. Compared to SS + AS and TENS, EMS + AS significantly increased PPT changes (F _(2,120) = 13.442, p < 0.001); however, there were no significant differences in PI or mean %MVC. Conclusions: This study demonstrates that EMS generates a local contraction instead of a full contraction for a muscle. EMS's effect is related to the aim of mimicking passive stretching performed by the therapist's hand. Ultimately, EMS + AS has the potential to be an effective approach for alleviating MPS symptoms.