The Effect of Postmortem Time and Freezer Storage on the Mechanical Properties of Skeletal Muscle

Investigators currently lack the data necessary to define the state of skeletal muscle properties within the cadaver. The purpose of this study is to define the temporal changes in the postmortem properties of skeletal muscle as a function of mechanical loading and freezer storage. The tibialis anterior of the New Zealand White rabbit was chosen for study. Modulus and no-load strain were found to vary significantly from live after eight hours postmortem. Following the dynamic changes which occur at the onset and during rigor mortis, a semi-stable region of postmortem, post-rigor properties occurred between 36 to 72 hours postmortem. A freeze-thaw process was not found to have a significant effect on the post-rigor response. The first loading cycle response of post-rigor muscle was unrepeatable but stiffer than live passive muscle. After preconditioning, the post-rigor muscle response was repeatable but significantly less stiff than live passive muscle due to an increase in no-load strain. Failure properties of postmortem muscle were found to be significantly different than live passive muscle with significant decreases in failure stress (61%) and energy (81%), while failure strain was unchanged. These results suggest that the post-rigor response of cadaver muscle is unaffected by freezing but sensitive to even a few cycles of mechanical loading.