The possibility of estimating muscle passive force from shear modulus using shear wave elastography (SWE) has been reported. However, the relationship between the elastic modulus and the passive force of human skeletal muscles, which is necessary for applications to the human body, has not been elucidated. This study investigates the elastic–passive force relationship in human skeletal muscles at multiple sites. One rectus femoris (RF) muscle was dissected from a Thiel embalmed cadaver. The proximal origin and distal quadriceps tendon were each immobilized with clamps of a pulley device. Calibration weights (0–450 g in 90 g increments) were applied to the distal tendon via a pulley system, and elasticity was simultaneously measured using SWE. The elasticity of the RF was measured at the proximal, central, and distal parts. The results demonstrated that the relationships between the SWE elasticity and the passive muscle force were linear for all the tested sites with coefficients of determination ranging between 0.973 and 0.999. Our study demonstrated that SWE may be used as an indirect method to measure passive muscle force at any site within a muscle in humans.
