[The mechanism of muscle contraction: along the path carved by Academician G.M Frank].

On the issue of the mechanism of muscle contraction, the views of the late G.M. Frank, to whom this symposium is dedicated, differed fundamentally from those of the then-current orthodoxy. Frank could not accept the idea of filament sliding brought about by swinging cross-bridges. He seemed particularly moved by two observations from his laboratory: the first, that the A-band shortened during active contraction; and the second, that sarcomere shortening occurred in stepwise fashion. From these findings principally, Frank came to the view that contraction involved a stepwise shortening of thick filaments. Although this view is broadly held to be incorrect, I will present evidence that it may constitute at least a partial answer. I will consider the evidence that both of Frank's principal findings-stepwise shortening and thick filament shortening-may be valid attributes of the contractile mechanism. I will then go on to show how these two attributes fit into an overall mechanism-not dissimilar to the one put forth by Frank.