Muscle function in carp during locomotion

Animals have different muscle fiber types: slow ones with a low maximum velocity of shortening (V_max) and fast ones with A high V_max. The advantages conferred by having different muscle fiber types have been assumed solely on the basis of in vitro experiments. These experiments show that efficiency and power production are both functions of V/V_max , the ratio between the velocity of shortening of a muscle fiber in vivo and its maximum intrinsic velocity of shortening.

To test these ideas concerning the role of different muscle fiber types, carp were used as an experimental model. The V_max of their slow and fast muscle fibers was determined. V, the velocity of shortening of muscle fibers, was determined from high speed motion pictures of swimming carp. The results show that during slow swimming, where they are used exclusively, the V/V_max of the slow muscle fibers corresponds to a position on their force-velocity curve where efficiency and power production are at a maximum. Similarly, during the very rapid escape response the fast muscle fibers are producing maximum power. The results also provide evidence that the fiber types are not functionally interchangeable, and that carp require both of them to execute the full range of movements in their locomotory repertoire.

Temperature affects the contractile properties of muscle with a Q₁₀ of about 2, and is expected to be an important environmental factor in determining the locomotory capacity of ectotherms. The experiments were repeated over a 10°C temperature range, and the results show that in spite of a 2-fold change in V_max, carp use their muscle fibers at max velocities where efficiency and power production are optimized.