Biomechanical response and post-intervention pain after dry needling, percutaneous electrolysis, and percutaneous electrical nerve stimulation on upper trapezius muscle

Background Dry needling (DN), percutaneous electrolysis (PE), and percutaneous electrical nerve stimulation (PENS) are invasive techniques widely used in musculoskeletal rehabilitation. While their clinical effects on pain have been investigated, their immediate impact on muscle biomechanical properties remains unclear. This study compared the short-term effects of DN, PE, and PENS on upper trapezius muscle tone and viscoelasticity in asymptomatic adults and evaluated post-intervention procedural pain as an index of tolerability. Methods In this randomized parallel-group trial, sixty asymptomatic adults aged 18-65 years were allocated to DN (n = 20), PE (n = 20), or PENS (n = 20), all applied under ultrasound guidance. Muscle mechanical properties (frequency, stiffness, elasticity, relaxation and creep) were assessed using MyotonPRO before and immediately after the intervention. Post-intervention procedural pain was rated on a visual analog scale. Linear mixed models were used to assess time, group and interaction effects, and between-group differences in procedural pain were analysed with one-way analysis of variance and, as a sensitivity analysis, the Kruskal-Wallis test. Results Significant time effects were observed for frequency (p = 0.002, partial R 2 = 0.16), elasticity (p = 0.009, partial R 2 = 0.11) and creep (p = 0.040, partial R 2 = 0.07). Frequency decreased, whereas logarithmic decrement (indicating lower elasticity) and creep increased, with mean changes below the minimal detectable change of the device. No significant group × time interactions were observed for any myotonometric variable. Procedural pain differed between groups: PE showed lower scores (0.45 ± 0.99) compared with DN (1.75 ± 1.29; p = 0.001, d = −1.228), corresponding to a large effect size. PENS yielded intermediate values (1.20 ± 0.83); in the non-parametric analysis, PE scores were also lower than those of PENS (p = 0.008). No significant correlations were found between mechanical changes and procedural pain. Conclusion DN, PE and PENS were followed by small and comparable immediate changes in upper trapezius mechanical properties. PE elicited the least procedural pain and was the best tolerated technique, which supports its consideration when tolerability is a priority. Confirmation in symptomatic and older populations is required.