Biomechanics of non-steady locomotion: Bone loading, turning mechanics and maneuvering performance in goats

The ability of animals to maneuver in their environment plays an important role in their survival, especially during predator-prey interactions, and thus factors in to the musculoskeletal design of locomotor systems. Though much previous work has focused on steady-state locomotion, non-steady behaviors that animals perform may carry even more selective importance. The goal of this dissertation was to examine the underlying mechanics of a variety of non-steady locomotor behaviors performed by a cursorial quadruped species in order to provide insight into the relationships between musculoskeletal design and locomotor performance. Looking first at the structural elements of the limbs, I measured in vivo bone strain patterns in two forelimb bones of goats to examine the effects of bone curvature on loading predictability under steady versus more natural outdoor conditions. I found that the curved radius showed less variability in strain orientations compared to the straighter metacarpus, but strains were still more variable during outdoor compared to treadmill locomotion. To investigate how upright quadrupeds maintain dynamic stability during high-speed turning, I analyzed stride-averaged ground reaction forces (GRFs) in relation to center of mass (COM) position, finding that goats closely aligned the net GRF with their virtual leg (the vector from center of pressure of GRF to the COM), similar to how humans riding on bicycles achieve balance by leaning into the turn. To address how each limb contributes to the overall turning dynamics, I analyzed linear and rotational impulses produced by individual limbs to deflect the COM heading and reorient the body in roll, pitch and yaw. Outside limbs produced greater turning impulses than inside limbs, as predicted by a simple static model based on limb and body geometry during turning. Finally, I assessed the effect of substrate traction on maneuvering performance using a novel metric of maneuverability. I found that dodging performance is three times greater on a natural grass surface compared to the indoor runway, despite the high friction of the runway surface. Non-steady maneuvers are inherently challenging to study, but they are nonetheless important for furthering our understanding of the design of locomotor systems.