Meeting Abstract
Muscles serve several different functions, arguably the most important of which is to do work and generate power to move the skeleton. Hill-type models are ubiquitously used to understand and predict how muscles perform this function in vivo. However, current models suffer from limited accuracy, particularly under submaximal dynamic conditions that typically occur during daily activities. While attempts have been made to incorporate effects into these models that are typically neglected, such as history and tissue mass effects, their relative influence on muscle performance has yet to be evaluated under common contractile conditions and muscle parameters. The purpose of this study was to develop a modeling framework that consists of a damped harmonic oscillator in series with a Hill-type muscle actuator. The base muscle is composed of a contractile and a parallel elastic element, and can be modified to incorporate additional elements such as inertial mass. The parameters of the harmonic oscillator, such as the damping and stiffness, were chosen to allow for muscle lengths and speeds that reasonably reflect the behavior of muscle in vivo. The model can be geometrically scaled while preserving the relationship between the forces of the harmonic oscillator and the maximum isometric force of the muscle, which allows the effects of modifying properties of the muscle to be evaluated at different muscle sizes while controlling for the behaviour of the harmonic oscillator. Time-varying muscle activations cause transient muscle forces that in turn drive the dynamics of the harmonic oscillator, allowing muscle work-loops to be tested. Thus, this modeling framework can be used to evaluate the relative influence of history-dependent, internal mass and activation effects on the mechanical behaviour of muscle during cyclic contractions.
