Publications

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.

Keywords: myofascial pain syndrome (MPS), transcutaneous electrical nerve stimulation (TENS), frequency–intensity parameters, pain reduction, muscle activity (sEMG)

This study compared the 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 activity in patients with myofascial pain syndrome (MPS). Both stimulation protocols showed comparable effects on pain, muscle tone, and cervical ROM, without significant intergroup differences, indicating similar clinical benefits. These findings indicate that both LFHI and HFLI electrical stimulation are effective non-invasive interventions for reducing pain and restoring neuromuscular function in individuals with MPS. While LFHI stimulation may provide prolonged analgesic effects through endorphin-mediated mechanisms, HFLI stimulation appears to facilitate improved muscle coordination and functional movement through rapid pain modulation based on the gate control mechanism. Clinically, electrical stimulation can be applied as a complementary and accessible treatment to relieve pain, decrease muscle hypertonicity, and improve movement performance in MPS patients.

Future studies should extend the intervention period and include follow-up assessments to examine the sustained effects of electrical stimulation on muscle fatigue, contraction onset and offset timing, and overall functional recovery.