Phenomenological consequences of sectioning and bathing on passive muscle mechanics of the New Zealand white rabbit tibialis anterior.

Skeletal muscle tissue provides support and mobility of the musculoskeletal system. Numerical modeling of muscle tissue aids in understanding disease pathophysiology, however, the effectiveness is dependent on accurately accounting for various tissue phenomena. Muscle modeling is made difficult due to the multitude of constituents that contribute to elastic and viscous mechanisms. Often, deterministic single fiber or fiber bundle studies are undertaken to examine these contributions. However, examination of whole, intact and structurally altered tissue and comparison to findings at the myofibril scale can help elucidate tissue mechanics. Stress relaxation tests at 10% strain were performed on 28 New Zealand White rabbit's tibialis anterior muscles for whole, intact muscle and sub-sectioned muscle samples. Additionally, to aid in examining viscous effects, sub groups were tested with and without a phosphate buffered saline bath. The steady-state elastic modulus was not significantly different between groups. Interestingly, sectioning did result in a negative Poisson's ratio following tensile loading. Additionally, sectioning resulted in altering the viscous tissue response as the time to reach steady-state was significantly faster than whole muscle samples (p<0.05), as well as the linear relaxation rate from 0 to 0.1 (p<0.01), 1 to 10 (p<0.05), and 10 to 100 s (p<0.05). Bathing tissue resulted in a significantly greater amount of percent stress relaxation for whole muscle (p<0.01). These findings provide new insight into the differing mechanical characteristics of whole and sectioned muscle tissue.