MUSCLE-CONTRACTION - THE STEP-SIZE DISTANCE AND THE IMPULSE-TIME PER ATP

We derive the step-size distance, and the impulse time per ATP split, from a consideration of Hill's energy rate equation coupled with the e nthalpy available per ATP split. This definition of step-size distance is model-independent, and is calculated to have a maximum of 17 Angst rom at no load and to reduce to zero at isometric tension, since it wi ll depend on the velocity of shortening. We revisit a derivation of Hi ll's force-velocity equation depending on impulsive forces working aga inst frictional forces and show that this gives a physical meaning to Hill's constants a and b. This is particularly elegant for Hill's cons tant b, which is directly related to the impulse time; the value of th is impulse time is 1/2 ms. The question that muscle contraction may in volve overlapping interactions is considered. However, we find that th e step-size distance is not dependent on the possibility of overlappin g interactions.