title: Elastic energy storage and radial forces in the myofilament lattice depend on sarcomere length.
abstract: We most often consider muscle as a motor generating force in the direction of shortening, but less often consider its roles as a spring or a brake. Here we develop a fully three-dimensional spatially explicit model of muscle to isolate the locations of forces and energies that are difficult to separate experimentally. We show the strain energy in the thick and thin filaments is less than one third the strain energy in attached cross-bridges. This result suggests the cross-bridges act as springs, storing energy within muscle in addition to generating the force which powers muscle. Comparing model estimates of energy consumed to elastic energy stored, we show that the ratio of these two properties changes with sarcomere length. The model predicts storage of a greater fraction of energy at short sarcomere lengths, suggesting a mechanism by which muscle function shifts as force production declines, from motor to spring. Additionally, we investigate the force that muscle produces in the radial or transverse direction, orthogonal to the direction of shortening. We confirm prior experimental estimates that place radial forces on the same order of magnitude as axial forces, although we find that radial forces and axial forces vary differently with changes in sarcomere length.
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Seattle, WA, USA. cdave@uw.edu
authors.forename: C David
authors.initials: CD
authors.lastname: Williams
authors.forename: Michael
authors.initials: M
authors.lastname: Regnier
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Daniel
mesh_terms: D001696:Biomechanical Phenomena; D019295:Computational Biology; D004548:Elasticity; D008954:Models, Biological; D009210:Myofibrils / Q000737:chemistry* / Q000378:metabolism; D009218:Myosins / Q000737:chemistry* / Q000378:metabolism; D012518:Sarcomeres / Q000737:chemistry* / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D009218:Myosins