Estimate of rate constants of muscle crossbridge turnover based on dynamic mechanical measurements.

A physiologically based model has been developed to fit measurements of the complex dynamic stiffness (Young's modulus) of isometrically held vertebrate skeletal muscle. Adjustments were made to accommodate isotonic conditions for comparison of model behavior with data on the rate of energy liberation vs. muscle shortening speed. The behavior of the muscle is well fitted to a second-order differential equation. This has made it possible to quantitatively estimate crossbridge rate constants of first (fA) and second (fB) stage attachment and detachment (gA and gB) based on Huxley's hypothesis of two-stage crossbridge attachment.