Mechanical response of human muscle at intermediate strain rates.

We experimentally determined the tensile stress-strain response of human muscle along fiber direction and compressive stress-strain response transverse to fiber direction at intermediate strain rates. A hydraulically driven materials testing system with a dynamic testing mode was used to perform the tensile and compressive experiments on human muscle tissue. Experiments at quasi-static strain rates were also conducted to investigate the strain-rate effects over a wider range. The specimens were loaded under stress equilibrium state for both the tensile and compressive experiments. The experimental results show that, at intermediate strain rates, both the human muscle's tensile and compressive stress-strain responses are non-linear and strain-rate sensitive. Human muscle also exhibits a stiffer and stronger tensile mechanical behavior along fiber direction than its compressive mechanical behavior along the direction transverse to fiber direction. An Ogden model with two material constants was adopted to describe the rate-dependent tensile and compressive behaviors of human muscle.