title: How does tissue preparation affect skeletal muscle transverse isotropy?
abstract: The passive tensile properties of skeletal muscle play a key role in its physiological function. Previous research has identified conflicting reports of muscle transverse isotropy, with some data suggesting the longitudinal direction is stiffest, while others show the transverse direction is stiffest. Accurate constitutive models of skeletal muscle must be employed to provide correct recommendations for and observations of clinical methods. The goal of this work was to identify transversely isotropic tensile muscle properties as a function of post mortem handling. Six pairs of tibialis anterior muscles were harvested from Giant Flemish rabbits and split into two groups: fresh testing (within four hours post mortem), and non-fresh testing (subject to delayed testing and a freeze/thaw cycle). Longitudinal and transverse samples were removed from each muscle and tested to identify tensile modulus and relaxation behavior. Longitudinal non-fresh samples exhibited a higher initial modulus value and faster relaxation than longitudinal fresh, transverse fresh, and transverse rigor samples (p<0.05), while longitudinal fresh samples were less stiff at lower strain levels than longitudinal non-fresh, transverse fresh, and transverse non-fresh samples (p<0.05), but exhibited more nonlinear behavior. While fresh skeletal muscle exhibits a higher transverse modulus than longitudinal modulus, discrepancies in previously published data may be the result of a number of differences in experimental protocol. Constitutive modeling of fresh muscle should reflect these data by identifying the material as truly transversely isotropic and not as an isotropic matrix reinforced with fibers.
authors.affiliation: Department of Mechanical Engineering, Colorado State University, Fort Collins, CO, USA.
authors.forename: Benjamin B
authors.initials: BB
authors.lastname: Wheatley
authors.affiliation: Department of Mechanical Engineering - Engineering Mechanics, Michigan Technological University, Houghton, MI, USA.
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Odegard
authors.affiliation: Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, USA.
authors.forename: Kenton R
authors.initials: KR
authors.lastname: Kaufman
authors.affiliation: Department of Mechanical Engineering, Colorado State University, Fort Collins, CO, USA; School of Biomedical Engineering, Colorado State University, Fort Collins, CO, USA. Electronic address: Tammy.Donahue@ColoState.edu.
authors.forename: Tammy L Haut
authors.initials: TLH
authors.lastname: Donahue
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D018482:Muscle, Skeletal / Q000166:cytology* / Q000502:physiology; D011817:Rabbits; D013048:Specimen Handling / Q000379:methods*; D013314:Stress, Mechanical; D013718:Tensile Strength
keywords: Constitutive modeling; Material testing; Mechanical properties; Rigor mortis