Cervico-Thoracic Fascial Densification and Altered Force Transmission Induced by Prolonged Smartphone Use: A Multimodal Ultrasonographic, Elastographic, and Electromyographic Investigation with Targeted Physiotherapy Modulation

Abstract Background: Smartphone-related neck disorders predominantly focus on postural kinematics and muscle activation patterns. The cervico-thoracic fascial system's role in altered load transmission during prolonged mobile device use remains uncharacterized. This study investigates fascial densification, shear-strain impairment, and myofascial force transmission dysfunction in smartphone users. Objective: To evaluate cervico-thoracic fascial biomechanical alterations in chronic smartphone users compared to controls, and to assess the efficacy of fascial-specific physiotherapy intervention in restoring load transfer mechanics. Methods: A prospective controlled trial enrolled 84 participants (42 smartphone-exposed ≥6 hours daily for ≥2 years; 42 matched controls <2 hours daily). Fascial stiffness was quantified via high frequency shear-wave elastography (SWE) at C4-C5 and T4-T5 levels. Dynamic fascial glide was assessed through B-mode ultrasonography during cervical flexion-extension and smartphone simulation postures. Superficial and deep cervical muscle recruitment patterns were evaluated via surface electromyography (sEMG) and intramuscular fine-wire EMG during graded cervical isometric flexion (12 N, 24 N, 36 N, 48 N). Cervical flexor endurance (CFE) was measured via pressure biofeedback dynamometry. Pressure pain threshold (PPT) at cervical, upper-thoracic, and lower-thoracic sites was determined via mechanical algometry. The intervention group (n=42) received 12 weeks of fascial-specific manual therapy combined with motor control retraining targeting deep cervical flexor–fascial coupling. Traditional cervical stabilization exercise served as the active control. Primary Outcome: Change in fascial shear modulus (kPa) from baseline to 12 weeks. Secondary Outcomes: Fascial glide displacement (mm), EMG recruitment ratio (deep:superficial normalized RMS), cervical flexor endurance time (seconds), PPT (kPa), and Neck Disability Index (NDI). Results: Smartphone users demonstrated significantly elevated cervico-thoracic fascial stiffness compared to controls (mean fascial shear modulus: 18.4±3.2 kPa vs. 11.6±2.1 kPa, p<0.001). Dynamic fascial glide was substantially impaired in the exposed group (glide displacement: 2.1±0.8 mm vs. 4.3±1.2 mm, p<0.001). Deep:superficial EMG recruitment ratio was significantly elevated, indicating preferential superficial muscle dominance (ratio: 0.42±0.15 vs. 0.68±0.18, p<0.001). Following 12 week fascial-specific intervention, exposed participants demonstrated significant improvements in fascial stiffness (reduction: 4.1±1.8 kPa, 22.3% change, p<0.001), fascial glide restoration (improvement: 1.8±0.9 mm, p<0.001), normalized EMG recruitment (improvement toward control values, p=0.002), and cervical flexor endurance (improvement: 18.4±8.6 seconds, p<0.001). The traditional exercise control group achieved modest improvements in endurance (9.2±6.4 seconds, p=0.031) with negligible changes in fascial metrics. NDI scores improved significantly more in the fascial-specific group (reduction: 8.4±3.2 points vs. 3.1±2.8 points, p<0.001). Conclusions: This investigation provides multimodal objective evidence that chronic smartphone use induces quantifiable cervico-thoracic fascial densification and compromised myofascial load transmission. Fascial stiffness represents a novel, biomechanically meaningful outcome reflecting functional impairment distinct from muscle activation patterns alone. Fascial-specific physiotherapy combining manual mobilization with motor control retraining targeting deep flexor–fascial coupling demonstrates superior efficacy compared to conventional exercise protocols, suggesting that addressing fascial substrate pathology should constitute a cornerstone of smartphone-related neck disorder management.