The dependency of shear wave velocity on muscle activation is inconsistent across muscles

Ultrasound shear wave velocity (SWV) is used to assess material properties of skeletal muscle, such as stiffness. Because specific tension and normalized short-range stiffness of muscle tissue vary linearly with activation and in a similar fashion across muscles with different architectures, we expect SWV to be consistent across muscles as well. We found instead that SWV differs across muscles with different architectures, under both active and passive conditions, even when controlling for passively and actively generated forces. As there was a weak correlation between SWV and architectural parameters such as pennation angle, it appears that variation of SWV may be dependent on other muscle properties that are different between muscles.