Dystrophin deficiency stiffens skeletal muscle and impairs elasticity: an in vivo rheological examination

Loss of dystrophin alters the biomechanical properties of skeletal muscle, including stiffness. Stiffness is typically assessed passively in excised muscle, but here we present the development of an in vivo rheological method to assess the mechanical properties of the tibialis anterior muscle in anaesthetized wild-type (WT; dystrophin-positive) and <i>mdx</i> (dystrophin-deficient) mice using a custom-designed apparatus compatible with an MCR 702 rheometer. To characterize stiffness, compressibility, and elasticity, rheological testing included compressive and shear strain protocols, along with recovery and assessments following contraction-induced strength loss. Relative to WT mice, the tibialis anterior of <i>mdx</i> mice was thicker, stiffer, and less compressible. These genotype differences aligned with hydroxyproline content, a marker of fibrosis. Postdeformation recovery was impaired in <i>mdx</i> mice under shear strain, and eccentric contraction-induced injury further increased stiffness and energy dissipation in the tibialis anterior of <i>mdx</i> mice. This rheological platform maintained the in vivo integrity of the tibialis anterior muscle of mice and consistently showed that storage and loss moduli can sensitively detect the detrimental impact of dystrophin deficiency on the in vivo viscoelastic properties of skeletal muscle. This rheological platform, termed myomechanical profiling, could be a viable and sensitive tool for assessing muscle quality and mechanical behavior of skeletal muscle, where viscoelastic properties are affected by disease.<b>NEW & NOTEWORTHY</b> Myomechanical profiling was developed using cyclic rheometry to assess the in vivo viscoelastic properties of mouse skeletal muscle-the in vivo environment is maintained alongside high measurement sensitivity and spatial resolution, and the ability to apply deformation transverse to fiber orientation. Myomechanical profiling was trialed in dystrophin-positive and dystrophin-negative (model of Duchenne muscular dystrophy) skeletal muscle, and showed that the loss of the biomechanical protein dystrophin increased stiffness and impaired elasticity after compressive and rotational shear deformation.