Comparative Effectiveness Randomised Controlled Trial of Hybrid Muscle Conditioning

Inclusion Criteria: * adults aged 18-50 years * unilateral CNSNP of more than 3 months' duration with mechanical nature (neck pain provoked or aggravated by cervical posture or movement) * baseline neck pain ≥3/10 on Numerical Pain Rating Scale (NPRS) * baseline functional disability ≤25/50 on Neck Disability Index (NDI) * baseline funcctional diability ≤60/100 on Disabilities of the Arm, Shoulder and Hand (DASH) * impaired deep cervical flexor performance verified by \<26 mmHg on craniocervical flexion test (CCFT) activation score (Jull et al., 2004) * positive scapular reposition test verified by an immediate reduction in pain or improvement in cervical range of motion during manual scapular repositioning (Van Dillen et al., 2007; Wannaprom et al., 2021) Exclusion Criteria: * neck pain caused by trauma or with a specific diagnosis (including radiculopathy, disc herniation, or spinal stenosis, or if neurological deficits or congenital cervical deformity) * history of previous surgery of the cervical or thoracic spine or shoulder * marked restriction of cervical mobility verified by extension \<30° or rotation \<60° (Cleland et al., 2010; Wainner et al., 2003) * inability to achieve full shoulder elevation required for the prescribed exercise * BMI ≥25 kg/m² * comoborities orthopaedic, neurological, or systemic conditions * high fear-avoidance beliefs verified by Tampa Scale for Kinesiophobia score ≥37 (Vlaeyen and Linton, 2000); psychological distress (SF-12 Mental Component Summary score ≤40) (Yu et al., 2015) * regular use of analgesics, muscle relaxants, or vasoactive medications * dizziness or vertigo suggestive of vestibular dysfunction or vertebrobasilar insufficiency * any contraindications to electrical stimulation for muscle endurance index measurement (any mental or neural implant, seizure)