title: Why animals have different muscle fibre types.
abstract: Animals have different muscle fibre types: slow fibres with a low maximum velocity of shortening (Vmax) and fast fibres with a high Vmax. An advantage conferred by the use of different fibre types during locomotion has been proposed solely on the basis of their in vitro properties. Isolated muscle experiments show that force generation, mechanical power production and efficiency are all functions of V/Vmax, where V is the velocity of muscle shortening. But it is not known whether animals actually use the different fibres at shortening velocities that are optimal for mechanical power production and efficiency. Here we compare the V of muscle fibres during locomotion with their Vmax. This comparison shows that during slow locomotion, the slow fibres shorten at a velocity that gives peak mechanical power and efficiency and the fast fibres shorten at their optimal velocity when powering maximal movements. Our results also show that maximal movements are impossible without fast fibres because the slow ones cannot shorten rapidly enough.
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia 19104.
authors.forename: L C
authors.initials: LC
authors.lastname: Rome
authors.forename: R P
authors.initials: RP
authors.lastname: Funke
authors.forename: R M
authors.initials: RM
authors.lastname: Alexander
authors.forename: G
authors.initials: G
authors.lastname: Lutz
authors.forename: H
authors.initials: H
authors.lastname: Aldridge
authors.forename: F
authors.initials: F
authors.lastname: Scott
authors.forename: M
authors.initials: M
authors.lastname: Freadman
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002347:Carps / Q000033:anatomy & histology / Q000502:physiology*; D003530:Cyprinidae / Q000502:physiology*; D007700:Kinetics; D008124:Locomotion; D009132:Muscles / Q000032:analysis / Q000502:physiology*; D012518:Sarcomeres / Q000648:ultrastructure