The crossbridge theory.

~,1247R. T. Tregear and ~. B. Marston 1Agricultural Research Council Unit of Muscle Mechanism and InsectPhysiology, Department of Zoology, University of Oxford, Oxford, EnglandINTRODUCTIONThis review treats the central issues in present-day research on the problemof contraction itself. In the first section we give a brief account of the severalschools of experimental study that have dominated the field over the lasthalf century and show how they have given rise to the crossbddge theory.In the second we describe more fully the logic of the present form of thetheory and the way in which different experimental modes interact toproduce this logic. The final section contains a brief commentary on theprobable developments in the near future. Because our article is fitted tovery strict limits on length, we have omitted much detail from the evidence.Many detailed reviews of particular aspects of the contractile process haveappeared in the last few years and may be used to add ttesh to our bare bones(17, 35, 40, 52, 72, 74, 77, 79, 82).PAST"Muscle, which is the instrument of voluntary movement ... becomesthicker, shortens and gathers itself together and so draws to itself and movesthe part to which it is attached" [Vesalius, 1543 (63)]. How it does so hasbecome a lot dearer in the last forty years, and is now almost a propersubject of molecular biology; the terms we use are approaching a descriptionof events during contraction at atomic resolution and millisecond timescale, but they are not there yet.The steady-state mechanics of active muscle were described in the firsthalf of the century in terms of the twin relations between force and either~Present address~ICI Pharmaceuticals, Mereside, Alderley Park, Macclestield, Cheshire,England7230066-4278/79/0301-0723 $01.00www.annualreviews.org/aronline Annual Reviews