Mechanics and kinematics of 90° turns in goats

MORENO, C.A.*; BIEWENER, A.A; Harvard University; Harvard University: Mechanics and kinematics of 90° turns in goats

The ability of animals to maneuver in their environment plays an important role in their survival, especially during predator-prey interactions. For terrestrial animals, vigorous changes of direction, linear accelerations and running turns can be almost daily requirements, but these behaviors have not been thoroughly studied because of their complexity and inherent experimental challenges. Recent work has begun to address turning mechanics in humans, cockroaches and mice. Our goal was to describe the kinematics and mechanics of 90° turns in an upright, cursorial quadruped, the goat, in order to determine how these animals initiate and execute running turns. We hypothesized differential roles for the forelimbs and hindlimbs: goats would initiate turns using their forelimbs to brake, provide lateral impulse and rotate the body axis. The hindlimbs would be used mainly to accelerate the COM linearly in the new heading. We used an infrared motion capture system to record goats running on an indoor track with a 90° turn. Four force plates were placed in the trackway to record GRFs in three dimensions from all four limbs. We calculated linear speed, body orientation relative to approach, shoulder and pelvic girdle orientations, lean angle of the body, parasagittal angle of the limbs, and heading of the COM, and examined these in relation to stance and swing phases. Preliminary analysis shows that goats generate body lean into the turn by repositioning their forelimbs towards the outside of the turn during swing phase, while using both forelimbs and hindlimbs to accelerate the COM in the new heading. Though difficult to study in an experimental setting, non-steady behaviors put a distinct set of demands on the musculoskeletal system, and therefore are important for understanding the relationship between locomotor demands and an animal�s morphology.

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