Meeting Abstract

6.4  Friday, Jan. 4  Incline hopping by kangaroo rats: Is there a division of labor? MCGOWAN, CP*; SHINE, C; University of Idaho cpmcgowan@uidaho.edu

Muscle-tendon specializations associated with specific modes of locomotion are often linked to trade-offs in function. In wallabies, the short, pinnate muscle fibers and long, thin ankle extensor tendons are well suited for elastic energy and return. However, they have a limited capacity to generate net mechanical work and control joint position. Because of this, there is a division of labor within the hind limb when performing tasks that require work to be done against the environment such hopping up an incline. Kangaroo rats share a similar hind limb morphology with wallabies, expect their ankle extensor tendons are relatively thicker and are thus better suited for generating work and controlling joint position. The goal of this study was to determine if a division of labor between proximal and distal muscles also exists during incline hopping by kangaroos rats, or if relatively thicker tendons enable all joints to contribute equally to raising the body’s center of mass. To test this, we collected data from desert kangaroo rats (D. deserti) as the hopped up a track inclined to 10, 15, 20 and 25 degrees. High speed video and ground reaction force data were combined in an inverse dynamics analysis to calculate the mechanical power and net work developed at each joint. Our results show that the net mechanical work done by the ankle is largely independent of slope, whereas the work done the hip and knee both increase significantly. At the highest slope, 44% of the positive mechanical work was developed by the hip, compared to 35% but he knee and 20% by the ankle. Therefore, similar to wallabies, muscles acting at the proximal joints are primarily responsible for modulating mechanical power output during incline hopping. However, the ankle extensors do contribute, suggesting that there is not a similar division of labor.