Acute effects of transcutaneous electrical nerve stimulation on passive muscle stiffness and pain in patients with neck pain: a parallel-group randomised controlled trial

Aims: Neck pain is a prevalent complaint often accompanied by increased cervical muscle stiffness. The aim of this study was to assess the immediate effects of transcutaneous electrical nerve stimulation (TENS), which is widely used for analgesia, on passive muscle stiffness and pain.

Methods: This randomised controlled trial was conducted according to CONSORT 2025 guidelines. Twenty-four adults (16 females, 8 males) with neck pain were randomly allocated to either the intervention group (IG) (n=12) or the control group (CG) (n=12). The IG received 20 minutes of bilateral TENS to the upper back and cervical region; the CG remained inactive for the same duration. The level of self-reported neck pain was measured using the Visual Analogue Scale (VAS). Muscle stiffness in the upper, middle, and lower trapezius, sternocleidomastoid (SCM), and cervical extensors was assessed with MyotonPro immediately before and after the intervention.

Results: The IG demonstrated significantly greater pain reduction than the CG (change in VAS:-2.83±0.58 vs -0.08±0.29; p<0.001). For muscle stiffness, the IG showed markedly larger decreases than the CG in the lower trapezius (-40.67±25.22 vs -5.17±8.00; p<0.001) and in the SCM (-29.42±18.03 vs -2.28±7.59; p<0.001). Changes in the middle trapezius (p=0.054) and cervical extensor (p=0.072), upper trapezius changes were not significant (p=0.846). Stiffness reductions in the SCM (r=0.722, R²=0.521) and lower trapezius (r=0.681, R²=0.464) strongly predicted pain improvement. Changes in the lower trapezius and
SCM stiffness together explained 66.1% of the variance in pain reduction (p<0.001).

Conclusion: A single TENS session provides immediate pain relief and reduces stiffness of the SCM and lower trapezius.