Meeting Abstract

S5.3-2  Sunday, Jan. 5 14:00  Using Anuran Landing as a Model for Studying Controlled Deceleration GILLIS, GB*; EKSTROM, L; AZIZI, E; Mount Holyoke College; Wheaton College; Univ. of California, Irvine

Anything that jumps must land, and unlike jumping, where muscles produce energy to accelerate the body into the air, landing requires muscles to dissipate energy to decelerate the body. Among anurans, toads (genus Bufo) are outstanding at landing, using their forelimbs to stabilize the body after touch-down as they slowly lower their hindlimbs to the ground. We have been using toads as a model to understand the biomechanics and motor control strategies of landing. Our results show that toads prepare for landing differently depending on how far they hop. For example, the forelimbs are more extended at impact during long hops than short hops. This kinematic trend is mirrored by predictable alterations in the intensity of pre-landing forelimb muscle activity, which tends to be more intense during long hops than short hops. These differences in forelimb kinematics and muscle activity seem to be associated with preventing muscles that are involved in dissipating energy after impact from stretching to overly long lengths. Indeed, a combination of in vivo and in vitro experiments has demonstrated that the elbow-extending anconeus, which is stretched during landing as the elbow flexes, rarely reaches lengths longer than those associated with the plateau of the muscle’s length-tension curve. We have also been studying how sensory information is involved in modulating landing preparation. Without vision, motor control patterns in major forelimb muscles appear unchanged from those in which sight is available. However, preliminary data from hops taken off elevated surfaces suggest that muscle recruitment patterns are altered in response to this perturbation. Taken together, these results suggest that toads rely less on vision than on proprioceptive and/or vestibular feedback to control landing.