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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 analyzed 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 R2 = 0.16), elasticity (p = 0.009, partial R2 = 0.11) and creep (p = 0.040, partial R2 = 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.

Keywords: dry needling, percutaneous electrolysis, percutaneous electrical nerve stimulation, upper trapezius, muscle mechanical properties, myotonometry, post-intervention pain

In asymptomatic adults, a single ultrasound-guided session of DN, PE or PENS applied to the upper trapezius was followed by small immediate changes in muscle mechanical properties, namely lower oscillation frequency and higher logarithmic decrement and creep, with no significant differences between techniques and with magnitudes below the minimal detectable change of the device. In contrast, the techniques clearly differed in tolerability: PE elicited the lowest procedural pain, significantly lower than DN, and also lower than PENS when the skewed distribution of pain scores was taken into account. These findings indicate that tolerability, rather than the immediate mechanical response, is the more discriminating criterion when choosing among these invasive techniques, and they position PE as a well-tolerated option for needling the upper trapezius. As this was a single-session study in a healthy sample without a sham control, these conclusions should be confirmed in symptomatic and older populations and over longer follow-up periods.