The Effects of Combined tDCS and Sling Exercise on Cervical Muscle Properties: A Randomized Controlled Trial

Objective: Neck instability and altered muscle activation are frequent contributors to musculoskeletal dysfunction. While sling exercise enhances proprioceptive input and neuromuscular control, transcranial direct current stimulation (tDCS) provides cortical modulation; however, their combined effects remain unclear. Therefore, this study compares the immediate effects of tDCS combined with a sling on cervical muscle changes, verifying peripheral and central approaches while exploring clinical applicability. Design: Randomized, controlled, single-blind, assessor-blind trial. Methods: Forty-five healthy adults aged20-30 years without recent neck or shoulder pain were randomly assigned tothree groups: sling exercise (SL), tDCS combined with sling (tSL), and tDCScombined with stabilization exercise (tST). The interventions had a duration of20 minutes, and the outcomes were assessed pre- and immediatelypost-treatment. Muscle tone,stiffness, and elasticity of the sternocleidomastoid (SCM) and upper trapezius(UT) were primarily measured. The secondary outcomes were SCM and UTthickness by musculoskeletal ultrasonography and pressure pain threshold (PPT)of the UT by algometry. Results: AAll groups had significantreductions in tone, stiffness, elasticity, and muscle thickness (p<0.05)with no statistically significantbetween-groupdifferences. The tSL group had the largest effect sizes, including left SCM tone (p<0.01, d=0.87), right SCMelasticity (p<0.05, d=0.85), and left UT tone (p<0.05, d=0.68). Therewere no statistically significant changes in PPT. Conclusions: Peripheral (sling) and central (tDCS) interventions acutely improvedcervical muscle mechanical properties, and their combination had the strongest effects, supporting the potential use of integrated neuromodulation and exercise approaches in future rehabilitation studies.