A A survey of the mainstream theories in the modern study of the mechanism of muscle contraction is made, with particular emphasis placed on the experimental results which most influenced the progression of ideas. Starting with early elastic and viscoelastic theories of muscle contraction, a chronological organization is used to present, in detail, the results leading up to the swinging crossbridge model. A brief review is made of the experimental results modifying the original crossbridge model such as transient state mechanics, in vitro kinetics, and kinetic measurements performed on demembranated muscle fibers. Following a brief synopsis of three of the more prevalent alternative models, a summary of the more relevant structural studies is presented. Finally, recent results pertaining to the mechanism of muscle contraction are presented and their promise for the future is discussed. (C) 1995 Academic Press, Inc.