PREDICTIONS OF THE TIME-COURSE OF FORCE AND POWER OUTPUT BY DOGFISH WHITE MUSCLE-FIBERS DURING BRIEF TETANI

The aim of this study was to identify the principal factors that deter mine the time course of force and power output by muscle during patter ns of stimulation and movement similar to those during fish swimming, Fully activated, white muscle fibres isolated from dogfish Scyliorhinu s canicula were used to characterize the force-velocity relationship o f the contractile component (CC) and the stress-strain relationship of the passive, elastic component (SEC) in series with the CC. A simple model of the time course of crossbridge activation during brief contra ctions was devised, Using the mechanical properties of the CC and SEC and the activation time course, force and power were predicted for bri ef contractions with constant-velocity movement and also for brief con tractions starting at various times during sinusoidal movement. The pr edicted force and power were compared with observations for these patt erns of stimulation and movement, The predictions matched the observat ions well for the period during stimulation, Matching of force was muc h less good for some specific conditions during relaxation, the period during which force persists after the end of stimulation, If either t he slow rise of activation or the SEC was omitted from the calculation , the predictions were poor, even during stimulation, Additional facto rs which may influence force are discussed, These include the after-ef fects of shortening and stretch, the variation of force during constan t-velocity stretch and non-uniform behaviour within the muscle.