S2-5 Thursday, Jan. 4 10:30 - 11:00 Size, history-dependent and dimensionality effects on muscle contraction WAKELING, JM*; ROSS, SA; RYAN, D; DOMINGUEZ, S; NIGAM, N; Simon Fraser University, Burnaby, Canada; Simon Fraser University, Burnaby, Canada; Simon Fraser University, Burnaby, Canada; Simon Fraser University, Burnaby, Canada; Simon Fraser University, Burnaby, Canada firstname.lastname@example.org http://www.sfu.ca/nml.html
During locomotion the muscles are often used in series of cyclic contractions. Much of what we understand about the performance of cyclic muscle contractions comes from work-loop experiments, but these are typically measured at a fibre-level scale. However, the contractile properties of muscle are affected by the dynamics of muscle size, and so raise questions about how whole-muscle performance can be predicted using data from smaller scales. Modelling studies aid in the understanding of muscle performance. Comparative studies commonly use a Hill-type muscle modeling framework that is derived from steady contractions and so may not account for unsteady and history-dependent effects that occur with cyclical contractions. Furthermore, Hill-type models typically do not include the dimensionality or base properties of the muscle, and both of these have been shown to influence force development. We developed a modeling framework to drive an oscillating inertial load using a Hill-type muscle actuator. The muscle was modified to include history-dependent effects, internal mass, and 3D geometry with base-material constraints, and was tested at different scales from single-fibre to whole muscle. The muscle was driven by a varying activation, and resulted in cyclic work-loops from which the force and power output could be determined. We report on the relative contributions of these muscle parameters to the overall contractile performance during cyclic contractions.