MORENO, C. A.*; MAIN, R. P.; BIEWENER, A. A.; Harvard University; Harvard University; Harvard University: Assessing bone loading under varying locomotor conditions: are bones uniformly loaded in different activities?

To build on knowledge gained from traditional steady state treadmill studies there is a growing need to characterize and evaluate musculoskeletal performance of animals during such nonsteady locomotor behaviors as accelerating, decelerating, jumping, landing and turning. Previous work has found uniform bone loading patterns across a range of speeds during steady state treadmill locomotion. However, during nonsteady locomotion (e.g. jumping), there is evidence that strain magnitudes in certain bones are greater and less predictable than during treadmill locomotion. Our goal was to evaluate the extent to which patterns of bone loading in the goat radius vary across a range of natural activities. Given the uniformity of musculoskeletal anatomy and bone curvature in the goat radius, we hypothesized that the cranial surface would be loaded in tension while the caudal and medial surfaces would be loaded in compression, consistent with previous findings for treadmill locomotion. We measured in vivo bone strains from the radial midshaft of juvenile goats performing a variety of nonsteady locomotor behaviors in an outdoor arena. We compared these data to steady state locomotion on a motorized treadmill. Similar to previous work, we found greater strain magnitudes and a greater range of strains during nonsteady activity compared to treadmill activity. In contrast to our hypothesis, while the medial surface of the radius was consistently loaded in compression, the cranial and caudal surfaces often experienced both tension and compression during certain activities. Although bone curvature may predispose the bone towards specific loading patterns during steady state locomotion, certain nonsteady behaviors will undoubtedly cause more unpredictable loading at the radial midshaft.