Simbios Talk by Sam Walcott, Cornell University, December 6, 2005

Title: Attempts to understand muscle: how the microscopic effects the macroscopic and vice versa.

For those that simulate human movement, it is of the utmost importance to have a reasonable macroscopic model of muscle.  Ideally, one would like a relationship between muscle force, muscle ATP consumption and dynamic variables (such as position, velocity and acceleration) of the links in the system.  To find such a relationship, it might seem best to perform a series of experiments on whole muscle and to use a "black box" approach.  However, for the past 50 years, most muscle experiments have been aimed at exploring the molecular machinery of muscle.  Much has been learned about the interaction between the proteins actin and myosin in muscle, and tens or hundreds of different molecular muscle contraction models have been proposed.  Thus, it might also seem best to adapt one of these models and to derive a simple relation that is most applicable to human movement situations.
To point out some of the advantages and disadvantages of each approach, I examine a macroscopic behavior of muscle called force enhancement (the observation that the magnitude of the fully-activated isometric steady-state force of contraction seems to be dependent on contraction history).  I propose a molecular explanation of this phenomenon, and explain its effects on macroscopic "black box" models.  Finally, I suggest that perhaps the optimal way to achieve the goal of a simple reliable model of muscle is to use a combination of macroscopic and microscopic experiments and theoretical models.