Fig. 1. (A) Example stress–strain curves for extension and retraction. Internal energy dissipation occurs as indicated by the hysteresis loss, the difference between input energy density and recoverable (stored) strain energy density. Input energy density is found as the area under the extension curve, while stored strain energy density is the hatched area under the retraction curve. (B) Loading of a M. flaccida specimen to maximum strain of approximately 0.35 demonstrates hysteretic loss.