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.