Power Output and Force-velocity Relationship of Live Fibres from White Myotomal Muscle of the Dogfish, Scyliorhinus Canicula

1. The relationship between force and velocity of shortening and between power and velocity were examined for myotomal muscle fibre bundles from the dogfish. 2. The maximum velocity of shortening, mean value 4-8 ± 0-2 (ms" 1 half sarcomere" (±S.E.M., N = 13), was determined by the 'slack step' method (Edman, 1979) and was found to be independent of fish length. 3. The force-velocity relationship was hyperbolic, except at the high-force end where the observations were below the hyperbola fitted to the rest of the data. 4. The maximum power output was 91 ± 14 W kg" wet mass (±S.E.M. , N = l) at a velocity of shortening of 1-3 ± 0-13/ims"halfsarcomere~ (±S.E.M. , N = 7). This power output is considerably higher than that previously reported for skinned fibres (Bone et al. 1986). Correspondingly the force-velocity relationship is less curved for intact fibres than for skinned fibres. 5. The maximum swimming speed (normalized for fish length) predicted from the observed power output of the muscle fibres decreased with increasing fish size; it ranged from 12-9 to 7-8 fish lengths s" for fish 0155-0-645m in length.