Our long-term goal is to improve treatments for musculoskeletal disorders associated with changes to the intrinsic properties of muscle. This project will determine if a novel application of shear wave elastography can facilitate this process by quantifying muscle stiffness noninvasively. The fundamental principle is that the velocity of shear waves is directly related to the local stiffness of the material in which they propagate. This relationship is well understood for homogeneous and isotropic materials (e.g. gelatin), but muscle is neither. Rather, it is an anisotropic composite of active and passive elements. Our objectives are to determine if shear wave elastography can quantify the intrinsic stiffness of whole muscle that emerges from its composite structure, and to infer how the integrity of its composite elements leads to this physiologically relevant metric. Our central hypothesis is that shear wave velocity (SWV) can be used to measure the net intrinsic stiffness of a muscle. Variants of this hypothesis have been widely assumed9-12. However, except for our preliminary data from cats, we are unaware of empirical evidence demonstrating that SWV provides a direct measure of muscle stiffness across a range of activations. We will explore the generalizability of these initial findings, and how they emerge from the microstructure of muscle in three specific aims. Our rationale is that providing an objective measure of intrinsic muscle stiffness and its contributing mechanisms will clarify the role of muscle in stiffness-related impairments, and lead to a personalized approach to treatment design and evaluation.

Collaborators:

• Eric Perreault
• Tom Sandercock
• Tom Royston
• Dieter Klatt
• Daniele Ludvig