Purpose Skeletal muscle is commonly modeled as a transversely isotropic medium; however, the behavior of its anisotropy under active loading remains insufficiently characterized. In this study, we used ultrasound time-harmonic elastography (THE) to quantify direction-dependent shear-wave speed (SWS) in the vastus lateralis (VL) muscle at rest and during low isometric contraction intensities. Methods Twenty-six healthy adults (...