This is the first book-length treatment of mathematical models of muscle functions. Although physiologists, biophysicists, and bioengineers often mention these models, particularly the important Huxley models, Thomas A. McMahon is the first completely to explain them. He addresses the questions "What makes the force in muscle?" and "How is this force controlled?" with precision and clarity, explaining his assumptions and retaining the steps in derivations so that the reader clearly understands the capabilities and limitations of the models. Using this procedure, he discusses, among other topics, the workings of the muscle spindle organ, the enhancement of running speed by "tuned track", and the evolutionary implications of scale. This book provides a framework for the many basic studies related to locomotion, which range from basic muscle mechanics and thermodynamics to coordinated motion. The author develops his comprehensive description of terrestrail animal locomoation by intergrating evidence from biochemical, physiological, morphological, and mechanical studies, without ignoring the complex ways in which these factors interact in the face of constraints imposed by size.