Meeting Abstract
103.4 Thursday, Jan. 7 A static model predicts the relationship between force and lean angle during dynamic turning in goats MORENO, C.A.*; BIEWENER, A.A.; Harvard University cmoreno@oeb.harvard.edu
Evasive maneuvers and turning behaviors are critical components of a terrestrial animal’s locomotor repertoire. To investigate the mechanics of such non-steady behaviors, we collected ground reaction forces (GRFs) and center of mass (COM) kinematics (speed, curvature) of goats as they trotted and galloped around a 90° turn. We first determined the roles of the individual limbs by comparing the linear and rotational impulses that each produced. In this study, we investigated the relationship between the lateral GRF produced by all four limbs and the body lean angle across a single turning stride. Body lean angle was defined as the angle between the global vertical and the vector from the goat’s collective center of pressure (COP) to its COM. We found a strong correlation between the lateral GRF and the centripetal force calculated from the COM kinematics. We also found that the relationship between lateral GRF and body lean closely matched the curve predicted by a steady-state geometric model (lean angle = tan-1 (GRFML/GRFVERT)). Interestingly, galloping strides fell above the predicted curve and trotting strides fell below the curve, possibly related to phase differences between the gaits. As predicted by the model, lean angle increased with speed for both trots and gallops. Comparing the body of a goat to a mechanical analog such as a car or a bicycle helps us understand the mechanism and trade-offs behind turning behaviors. At slow speeds, the animal acts more like a car: it simply redistributes forces among its four legs to produce the inward acceleration necessary to turn. At higher speeds, the animal becomes more bike-like: in addition to redistributing its limb forces, it also leans into the turn to a degree that is predicted by its mass, speed and COM trajectory.
