Detecting intervention-specific change in soft tissue mobility aligned with regional pain through optically measured skin surface strains

Purpose: Soft tissue manipulation (STM) is a widely used massage-based intervention for myofascial pain, yet its effects on soft tissue mobility are primarily assessed through subjective clinical observations. Mechanical changes underlying symptom relief therefore remain unclear. No objective gold standard exists; current methods either measure stiffness in small regions, missing lateral mobility between fascial layers, or rely on clinical palpation. Optical measurement of tissue mobility from the skin surface offers an objective approach compatible with clinical practice. Methods: Digital image correlation captured skin surface deformation during hands-on assessment of the cervicothoracic region. Nineteen participants underwent a standardized STM protocol. Tissue mobility was measured immediately before and after intervention, considering tissue pull direction (superior vs. inferior) and bilateral anatomy (left vs. right). Eleven strain-based biomarkers evaluated tissue glide and deformation. Results: Several biomarkers changed significantly following intervention, with maximum pull increasing 3.4 mm. STM produced tissue mobility changes in nearly all treated participants, with 88% improving on at least one body side. Among participants with baseline bilateral pain asymmetries, 90% showed greater mobility gains on their more painful side. Bilateral mobility asymmetries were observed in 53% of participants, eight of whom reported pain asymmetries; in all cases, the less mobile side corresponded to the more painful side. Conclusion: Optically derived tissue glide and deformation measures can objectively detect soft tissue mobility changes immediately following STM. Mobility gains align with self-reported pain, supporting the clinical relevance of strain-based biomarkers and their potential to complement clinical assessment of myofascial restriction and therapeutic response.