In Vivo Assessment of Lower Limb Muscle Stress State Based on Shear Wave Elastography

This study aims to explore the possibility of assessing muscle stress state using shear wave elastography (SWE). Eight healthy males participated in the measurements, and the Young's modulus of 10 leg muscles of each participant were measured in six standard positions: lying, sitting, and four quasi-static walking postures. The contributions of each muscle in the four quasi-static walking postures were examined, and the relationship between the Young's modulus and simultaneously recorded plantar pressure was preliminarily explored for the most significant muscles. Results indicate that ICC3,1 ranges from 0.941 to 0.998, and 95% CI is in the range 0.909-0.999, CV ranges from 1.45% to 9.5%, and SEM ranges from 0.026 kPa to 0.824 kPa for all the tested muscles. This indicates that the Young's modulus of the muscles, measured by SWE, showed excellent retest reliability. In the lying and sitting positions, significant differences were observed in Young's modulus of 9 muscles with the only exception of biceps femoris (BF). In the heel strike and push off positions, strong linear relationships were found between the plantar pressure and Young's modulus of gastrocnemius medialis (GM) suggesting that muscle SWE measurement may be a good indicator of ground reaction forces. This study demonstrates that the SWE measures of the muscle Young's modulus can be used to reliably reflect the quantitative change in the stiffness of a muscle at different positions, and may also be employed to estimate the ground reaction forces and muscle stress state. Although this is a great progress in studying muscle force, it is still a great challenge to measure the Young's modulus of muscle and noninvasively evaluate the muscle force in vivo using SWE.