Defining Muscle Elastance As A Parameter

Functional descriptions of striated muscle are often based on the measured variables force and initial velocity of shortening, embodied as Hill´s contractile element. The fundamental difficulty of describing the mechanical properties of muscle with a force-velocity relation that is set a priori, and the practical problem of the act of measurement changing muscle´s force-velocity relation or elastance curve, are described. As an alternative, a new model of muscle contraction is presented, which characterizes muscle´s contractile state with parameters, rather than variables. Muscle is treated as a force generator that is time, length, and velocity dependent. Muscle dynamics develop from a single equation based on the formation and relaxation of crossbridge bonds. This analytical function permits the calculation of muscle elastance via E_m = partf_m/partlscr_m. This new muscle model is defined independently from load properties, and muscle elastance is dynamic and reflects changing numbers of crossbridge bonds. This parameter is more representative of the mechanical properties of muscle than are variables such as muscle force and shortening velocity.