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 enthalpy available per ATP split. This definition of step-size distance is model-independent, and is calculated to have a maximum of 17 A at no load and to reduce to zero at isometric tension, since it will depend on the velocity of shortening. We revisit a derivation of Hill's force-velocity equation depending on impulsive forces working against frictional forces and show that this gives a physical meaning to Hill's constants a and b. This is particularly elegant for Hill's constant b, which is directly related to the impulse time; the value of this impulse time is 1/2 ms. The question that muscle contraction may involve overlapping interactions is considered. However, we find that the step-size distance is not dependent on the possibility of overlapping interactions.
Worthington
C R
CR
Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Elliott
G F
GF
D000199:Actins / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000502:physiology*; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D009218:Myosins / Q000502:physiology
D000199:Actins; D000255:Adenosine Triphosphate; D009218:Myosins