The step-size distance in muscle contraction: properties and estimates

The step-size distance in muscle contraction is obtained using the step-size distance equation z = u/n, where z is the step-size distance, u is the actin filament velocity and n is the ATPase rate of splitting. In a previous study a step-size distance of about 17 Å at no load was determined for intact frog muscle. Some properties of the step-size distance equation are described. We have now made estimates of the step-size distance z for a variety of muscles using existing physiological and biochemical data in the literature. The estimates are listed in Tables 1 and 2. We find that the step-size distances are clustered in the range 13–17 Å for nearly all muscles.