Meeting Abstract

67.1  Monday, Jan. 6 08:00  In vivo Femoral Strains in Swimming Turtles: Influence of Locomotor Medium on Limb Bone Loading YOUNG, V.KH.*; BLOB, R.W. ; Clemson University; Clemson University vkhilli@clemson.edu

Many terrestrial vertebrate lineages have members that have returned to aquatic habitats. Such taxa often show characteristic changes in limb bone shape, such as flattening of the shaft. The basis for evolutionary modifications in skeletal structure is often assumed to relate to changes in the loads that bones experience. Shifting to aquatic habitats would be expected to alter the loads to which limbs are exposed, lowering body support demands but retaining muscle forces from cyclic activity. No experimental data are available to evaluate such predictions, however, or to specify changes in load magnitude or regime between habitats. We tested how limb bone loading changes between use in terrestrial and aquatic habitats by recording in vivo strains from femora of swimming turtles, and comparing these data to strain recordings from turtle femora during terrestrial walking. We predicted that peak load magnitudes would be lower during swimming than walking, but that nearly equal load peaks, indicating bending in opposite directions, might occur during each of the thrust and recovery phases of the limb cycle. Preliminary data indicate our first prediction was met, with average peak strains in swimming less than half the magnitude of those during walking. Loading regimes were consistent between swimming and walking, with compressive axial strains experienced on the dorsal surface of the femur. Thus, our second prediction was not met, as single peaks of loading were consistently experienced during the thrust phase, whereas loads during recovery were more variable and typically much lower in magnitude than the strains recorded during thrust. These results indicate the strong role that limb muscles play in producing bone loads even after the reduction of environmental forces.