Noninvasive tools for assessing muscle structure and function

Project Summary Pathological changes in muscle stiffness can result from disease, blunt trauma, overuse, or as secondary complications from other injuries and treatments. Changes in muscle stiffness can lead to reduced mobility, chronic pain, discoordination, and increased rate of injury. Consequently, many therapeutic interventions target muscle or joint stiffness. While there is a long history of measuring joint stiffness, there are no validated methods to directly quantify the intrinsic stiffness of individual muscles independently from the other factors influencing the mechanics of a joint. This is a major obstacle to identifying, treating, and monitoring muscle contributions to stiffness-related impairments. Our long-term goal is to improve treatments for musculoskeletal disorders associated with changes to the intrinsic properties of muscle. The central hypothesis of this proposal is that ultrasound elastography (USE), a relatively new imaging tool for the clinic, can be used to measure the intrinsic stiffness of living muscles. Variants of this hypothesis have been widely assumed, but not directly tested aside from the preliminary data we have provided. Our rationale is that providing an objective measure of intrinsic muscle stiffness will clarify the role of muscle in stiffness-related impairments, and lead to a personalized approach to treatment design and evaluation. We will evaluate our central hypothesis with three aims. Aim 1 will determine the extent to which elastography can measure the intrinsic stiffness of muscles during active contractions. This will be completed in architecturally different muscles of the cat hind limb, where activation can be controlled precisely and direct mechanical measures obtained for comparison. Parallel human experiments will assess feasibility in clinically relevant settings, when muscle is activated by normal patterns of recruitment and rate modulation. Aim 2 will determine if substantial passive forc