Comparative Effects of Low-Frequency High-Intensity and High-Frequency Low-Intensity TENS on Neuromuscular Activation in Myofascial Pain Syndrome: A Randomized Controlled Trial

Abstract Myofascial pain syndrome (MPS) of the upper trapezius is characterized by trigger-point–related pain, restricted cervical motion, and altered muscle activation patterns. Electrical stimulation is a widely used noninvasive intervention, yet the influence of different frequency–intensity combinations remains insufficiently defined. This randomized controlled trial compared the short-term effects of low-frequency high-intensity (LFHI) and high-frequency low-intensity (HFLI) transcutaneous electrical nerve stimulation (TENS) on pain, cervical range of motion (ROM), muscle tone, and muscle activation in adults with upper trapezius MPS. Thirty participants were randomly assigned to either the LFHI or HFLI protocol and received 20-minute treatments twice daily for five days. Pain intensity (numeric rating scale), pressure pain threshold, cervical ROM, upper trapezius muscle tone, and surface electromyography (sEMG) of the upper trapezius, middle deltoid, and levator scapulae were assessed before and after intervention. Both LFHI and HFLI stimulation significantly reduced pain intensity and increased pressure pain threshold ( p < .01). Cervical ROM in all directions improved significantly in both groups ( p < .01), accompanied by reductions in upper trapezius muscle tone ( p < .01). sEMG analysis revealed decreased upper trapezius and levator scapulae activity and increased deltoid activation in both groups ( p < .01). Although no significant intergroup differences were observed for most parameters, the deltoid-to–upper trapezius activation ratio increased significantly only in the HFLI group ( p < .05), indicating a more favorable motor recruitment pattern. These findings demonstrate that both LFHI and HFLI electrical stimulation protocols effectively relieve pain, reduce muscle hypertonicity, and enhance cervical mobility in individuals with MPS. While clinical outcomes were comparable, HFLI stimulation may provide additional benefits in normalizing shoulder muscle activation. Electrical stimulation represents a practical and accessible modality for restoring short-term neuromuscular function in MPS.