Dynamic and elastic stiffness of the semitendinosus muscle after knee joint immobilization in rats.docx

We clarified the maximum limit of the semitendinosus muscle length <i>in vivo</i> was equivalent to 110% of slack length, which was taken as the limit of the physiological range. To evaluate mechanical features representing muscle stiffness within and beyond the limits of physiological muscle length, quadratic functions were fitted separately to the dynamic and elastic tension-strain curves at strains of 2.5%–10% <i>Ls</i> as the small strain and at strains of 7.5%–20% <i>Ls</i> as the large strain. The stiffness for small strains was then estimated by calculating the tangents at strains of 5% and 7.5% <i>Ls</i> of the quadratic fit to four points (strains of 2.5%, 5%, 7.5%, and 10%<i> Ls</i>), while stiffness for large strains were similarly estimated from the tangents for strains of 10% and 15% <i>Ls</i> of the quadratic fit to four points (strains of 7.5%, 10%, 15%, and 20% <i>Ls</i>).