Abstract
Exercise prescription for Duchenne muscular dystrophy (DMD) is complicated by the susceptibility of unstable skeletal muscle to eccentric contraction-induced damage. Although evidence suggests that isometric contractions can confer molecular and physiological benefits to DMD muscle, their impact on viscoelastic properties has not been assessed in vivo. We examined the effects of injurious eccentric contractions and non-injurious isometric fatiguing contractions on the biomechanical properties of dystrophin-positive and dystrophin-negative skeletal muscle. Given that DMD is characterized by muscular instability due to the absence of dystrophin, we employed myomechanical profiling—a custom apparatus compatible with an MCR702e rheometer—to evaluate stiffness, compressibility, and elasticity of skeletal muscles in male mice. Anterior crural muscles in anaesthetised dystrophin-positive (wildtype) and dystrophin-negative (mdx) mice were electrically stimulated in vivo to complete a series of 50 eccentric contractions or a series of submaximal isometric fatiguing contractions. Biomechanical properties of wildtype and mdx tibialis anterior muscle were then immediately characterized using myomechanical profiling. Fatigued tibialis anterior muscle in wildtype and mdx mice required greater force to statically compress to similar depths. Under rotational shear strain, eccentric contractions increased stiffness in mdx tibialis anterior muscle only, while isometric fatiguing contractions increased stiffness in wildtype muscle but not in mdx muscle. In dystrophin-deficient skeletal muscle, eccentric exercise increases stiffness but fatiguing isometric exercise does not negatively alter muscle biomechanics. Prescribed exercise for patients with DMD remains a controversial topic but our findings indicate that dystrophin-deficient skeletal muscle is biomechanically resilient to isometric fatigue.