title: Muscle, joint, and tendon contributions to the torque profile of frog hip joint.
abstract: The relative contributions of muscle force, moment arm, and tendon compliance were determined as a function of joint angle in the frog semitendinosus-hip joint system. Muscle, joint, and tendon properties were individually measured and then combined to predict the torque generated at the hip joint as a function of joint angle (i.e., the hip torque profile). Predicted torques were then compared to experimentally measured torques using a stepwise regression model to quantify the relative importance of muscle, joint, and tendon contributions to the hip torque profile. Variation in moment arm accounted for 74% of the variability observed in the hip torque profile, while addition of the muscle's intrinsic sarcomere length-tension property accounted for an additional 19% of the torque profile variability. Tendon compliance, which permitted a small amount of sarcomere shortening, accounted for only about 4% of the torque profile variability. We conclude that in this muscle-joint system, the relative fiber length-to-moment arm ratio is the major determinant of the shape of the isometric joint profile. The fiber length-to-moment arm ratio in other mammalian systems is also discussed.
authors.affiliation: Department of Orthopedics, University of California, San Diego.
authors.forename: R L
authors.initials: RL
authors.lastname: Lieber
authors.forename: S D
authors.initials: SD
authors.lastname: Shoemaker
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D006621:Hip Joint / Q000502:physiology*; D008954:Models, Biological; D009132:Muscles / Q000502:physiology*; D011894:Rana pipiens / Q000502:physiology*; D012518:Sarcomeres / Q000502:physiology; D013710:Tendons / Q000502:physiology*