Meeting Abstract
Different surface substrates change the ability of an animal to generate the ground contact forces that propel locomotion. Thus, the overall behavior of the locomotor pattern, namely the coordination of the movement, may change drastically. However, specific animals may be well adapted to locomotion on different substrates given that they experience those substrates in their natural environment. To address this question, we compared the kinematics of the kangaroo rat (Dipodomys deserti) while hopping either on a solid surface or on sand. High speed video was used to record the kinematics of 6 animals while hopping on a specially designed rotatory treadmill upon which we were able to place sand or have just the bare wooden surface. Visual markers on the midfoot, ankle, knee, hip, and pelvis were digitized and joint angles calculated. We found that for comparable speeds, the contact time with the ground was longer and was a greater percentage of the hop cycle on sand versus the solid surface. This result was expected given the physics of the sand extended the time to decelerate and accelerate the foot. The velocity of the pelvis, which is close to the center of mass of the animal, were remarkably similar, showing that the overall hopping movements on each surface were similar. The distinctive difference between hopping on the two surfaces was the posture of the animal, in that the average length of hindlimb (measured as the distance between the midfoot and hip) was longer for hopping on the solid surface. This result showed that a more crouched posture was adopted by the animal for hopping on the sand to compensate for the different biomechanical demands of the sand surface.
