Summary

Force and heat production were measured during isovelodty shortening of tetanized white myotomal muscle fibres from the dogfish at 12 °C. For each fibre preparation a range of velocities was used. Mechanical power was calculated from force x velocity of shortening. The rate of total energy output during shortening was evaluated as the sum of mechanical power and the rate of heat production. The ratio of mechanical power to total energy rate was taken as a measure of efficiency of energy conversion to mechanical power during shortening. Efficiency was maximal and varied little in the range of shortening velocities 0.42-0.89 fibres lengthss"1 (0.11-0.23 Vmm); maximal efficiency was 0.33±0.01 (±S.E.M., N=23 measurements on seven fibre bundles). The efficiency of the white fibres from dogfish was less than that measured in the same way in earlier experiments on frog muscle and tortoise muscle