Ability of skeletal muscle to protect bones and joints from external impacts: Acoustical assessment

Abstract

One of the least studied functions of skeletal muscle is its role in protecting the skeletal system from external impacts by absorbing and redistributing the energy of mechanical shock in time and space. During muscle contraction its elasticity modulus is greatly increased which partly unloads adjacent bones and skeletal joints and its viscosity is also greatly increased helping to absorb and dissipate dangerous shocks. Elasticity and viscosity data may be obtained using the measurement of shear wave velocity and attenuation. In this study changes in the velocity and attenuation of shear acoustic waves in an anisotropic tissue phantom mimicking skeletal muscle under different level of tension of the fibers embedded in the phantom is investigated. Stretching the fibers simulates the muscle contraction. It is shown that velocity of shear waves significantly increase with fiber tension in the case of a wave propagating along the fibers and is negligibly affected in the case of wave propagation across the fibers. A theory has been developed for propagation of shear waves in anisotropic medium simulating the muscle and muscle contraction. Equations for the speed and attenuation of shear acoustic waves are derived. Theoretical predictions are in agreement with experimental data.