BACKGROUND: Cervical disc herniation (CDH) is a common musculoskeletal disorder characterized by chronic neck pain, impaired proprioception, kinesiophobia, and functional limitations, often requiring multimodal conservative care. Myofascial techniques, including Instrument-Assisted Soft Tissue Mobilization (IASTM) and percussion massage therapy (PMT), have emerged as supportive physiotherapy interventions. This randomized controlled trial compared the effects of IASTM and PMT on pain, disability, kinesiophobia, and proprioceptive function in individuals with CDH. METHODS: In this double-blinded RCT, 57 participants with CDH were randomly allocated to Conventional Therapy (CT), CT + PMT, or CT + IASTM (n = 19 each). Interventions were delivered three times per week for 3 weeks. PMT was applied with a percussion massage device (33-40 Hz) for 3 min to each target muscle group (trapezius, levator scapulae, cervical paravertebral) using longitudinal strokes. IASTM used stainless-steel tools on trapezius, splenius, and suboccipital muscles, with sweep and fan techniques at 30°-60°, for 9 min per session. Primary outcomes were pain (VAS) and disability (NDI); secondary outcomes included kinesiophobia (TSK) and joint position sense (JPS). Between-group differences were analyzed using ANCOVA with baseline values as covariates. RESULTS: All groups showed significant within-group improvements across all outcomes (p < 0.001). Compared to CT, both PMT and IASTM produced greater improvements in pain, kinesiophobia, and JPS (p < 0.001). VAS-rest reductions were - 4.00 ± 0.89 (d = 4.49) for IASTM, - 3.38 ± 1.95 (d = 1.74) for PMT, and - 2.13 ± 1.49 (d = 1.43) for CT. VAS-activity decreased by - 4.89 ± 1.44 (d = 3.41) for IASTM and - 3.89 ± 1.84 (d = 2.11) for PMT. NDI improved by - 11.47 ± 4.23 (d = 2.71) in IASTM, - 12.11 ± 6.86 (d = 1.76) in PMT, and - 6.63 ± 5.47 (d = 1.21) in CT, all exceeding the MCID threshold of 7.5 points. JPS-flexion improved by - 3.80 ± 1.61 (d = 2.36) in IASTM, - 3.67 ± 1.34 (d = 2.73) in PMT, and - 1.09 ± 0.84 (d = 1.29) in CT. Similar patterns occurred for extension, right rotation, and left rotation. Overall, IASTM and PMT yielded comparable improvements, suggesting similar clinical efficacy. CONCLUSIONS: IASTM and PMT provide added benefits over conventional therapy alone in managing CDH, especially in reducing pain and kinesiophobia and enhancing proprioception. Both can be effectively integrated into conservative rehabilitation programs targeting sensorimotor deficits in CDH. TRIAL REGISTRATION: Prospectively registered in the ClinicalTrials.gov registry (NCT06903000) on 24/03/2025.