The explosive jumps of frogs represent a dramatic locomotor behavior that might be expected to place substantial loads on the limb skeleton. Our measurements of in vivo strains from the femur of jumping frogs have indicated only moderate load magnitudes, though these recordings have shown a complicated loading regime that combines axial and bending loads with variable degrees of torsion. To help understand the mechanics underlying the loading regimes identified during strain recordings, we synchronized measurements of three-dimensional ground reaction force components acting on a single limb with measurements of three-dimensional limb kinematics in jumping bullfrogs (Rana catesbeiana) and cane toads (Bufo marinus). The vertical component of the ground reaction force frequently exceeded one body weight in magnitude during jumps, but the mediolateral component was usually much smaller. Bending ad torsional loads, therefore, are likely related primarily to the inclination of the limb relative to a primarily vertical ground reaction force, rather than inclination of the ground reaction force itself. Small mediolateral forces also have been found previously in other species using non-parasagittal locomotion (e.g., lizards, alligators), and thus appear to be common among diverse modes of locomotion in vertebrates.
Available at: http://works.bepress.com/megan_sheffield/4/