NELSON, F.E.*; GABALDON, A.M.; ROBERTS, T.J.: Force-velocity Properties of an Avian Hindlimb Muscle

Recent work has provided measurements of power output in avian skeletal muscles during running and flying, but little is known about the force-velocity properties or instantaneous power capacity of avian skeletal muscle. We made in situ force-velocity measurements of a major hind limb power producer, the lateral gastrocnemius, in four wild turkeys (Meleagris gallopavo). The majority of muscle fibers in galliform gastrocnemius are classified as Type II, fast fibers. Since avian and mammalian runners share many common features of running mechanics, we predicted turkey lateral gastrocnemius muscle contractile properties would be similar to fast fibers of an equivalently sized mammal. The sciatic nerve was isolated for supra-maximal nerve stimulation and the tendon of the lateral gastrocnemius muscle was attached to an Aurora Servo Motor model 310B-LR for measurements of force and velocity. We measured isotonic force-velocity properties for at least six different loads. All measurements were made over the plateau region of the length-tension curve. The Hill equation was fitted to the data to determine maximum shortening velocity and peak instantaneous power output. The maximum shortening velocity determined for the whole muscle was 13.1&plusmn1.1 L/s (mean&plusmnS.E.), similar to the 12.6 L/s predicted from scaling equations for mammalian skeletal muscle fibers. The maximum isometric force was 271&plusmn28 kPa, which is within the range of published values for mammalian skeletal muscles. Peak instantaneous power of the muscle was 341.7&plusmn36.4 W/ kg. The mechanical properties of turkey lateral gastrocnemius skeletal muscle do not reveal any fundamental differences in the mechanical function of avian and mammalian