Hill-Based Muscle Models: A Systems Engineering Perspective

Chapter 1 (Zahalak) provided a brief historical treatment of the early findings that led to the muscle model structure first proposed by A. V. Hill (1938). From a “systems engineering” perspective, this is a phenomenologically based, lumped-parameter model that is based on interpretations of input-output data obtained from controlled experiments. Simply stated, this model consists of a contractile element (CE) that is surrounded, both in series and in parallel, by “passive” connective tissue (Figure 5.1). CE is furthermore characterized by two fundamental relationships: CE tension-length and CE force-velocity. Each of these is modulated by an activation input that is structurally distinct from the location for mechanical coupling between the muscle and the environment (Figure 5.1).