Strain-based biomarkers at the skin surface differentiate asymmetries in soft tissue mobility associated with myofascial pain

Soft tissue manipulation is used widely to assess myofascial tissue qualitatively but lacks objective measures. To quantify the mobility of myofascial tissue, this effort derives optical biomarkers from the skin surface, as observed in the hands-on workflow of clinicians. Digital image correlation using three high-resolution cameras captures the cervicothoracic region as a clinician deeply engages and stretches the skin and myofascial tissue. Nineteen participants were positioned prone and marked with semi-permanent tattoos, optimized for tracking tissue without compromising its natural mechanics. Tissue mobility was then clinically assessed both bilaterally (left and right sides of body) and directionally (superior and inferior directions of pull). Eleven strain-based biomarkers were derived per tissue pull. With participants' data aggregated, the sides of the body were indistinct, though pull in the superior direction was distinct from that in the inferior direction. Given substantial variance in the biomarkers’ absolute values between participants, we then evaluated each person individually. Therein, distinct tissue behaviors were observed. In particular, bilateral differences were identified in nine participants, eight of whom reported discrepancies in pain between their left and right sides, while directional distinctions were observed in sixteen participants, as expected given similar anatomical tissue structures between individuals. In our sample of participants, optical skin surface tracking and derived strain-based biomarkers identified asymmetrical distinctions in bilateral mobility, which correspond with self-reported pain. Such objective assessment of myofascial tissue stiffness is important in monitoring and treating chronic musculoskeletal pain, which afflicts half of the U.S. adult population.