Meeting Abstract
P3.63 Tuesday, Jan. 6 Collisional mechanics during sifaka bipedalism BAUMGARTNER, R.E.; WUNDERLICH, R.E.*; SCHMITT, D.; Duke University, Durham, NC; James Madison University, Harrisonburg, VA; Duke University, Durham, NC wunderre@jmu.edu
Minimization of the energetic cost of locomotion may be an influential selective factor for mammalian gait choice and kinematics. One significant cost during terrestrial locomotion is the work limb muscles must do to redirect the center of mass (COM) from generally downward to generally upward. Ruina et al (2005) have detailed a model in which redirection of the COM is described as a collision whose energetic costs during locomotion can be reduced by minimizing the number of collisions, sequencing multiple limb contacts during a collision, or simulating an elastic collision in which the incoming and outgoing velocity vectors create the same angle relative to the substrate reaction resultant. In order to test the hypothesis that animals will choose gait patterns that minimize collisional energy loss, we examined the unusual bipedal galloping gait used by sifakas. Two adult sifaka were videotaped at 250 Hz during bipedal locomotion across a long force platform. Collisions per stride, limb contacts per collision, and pseudo-elasticity of collisions were examined. The latter was calculated as the angle of the COM velocity to the substrate reaction resultant before and after the redirection of the COM. Our results support the hypothesis that the bipedal galloping gaits of sifaka minimize collisional energy loss by: 1) reducing the number of collisions that occur during each stride to one (walking and running humans have two), 2)sequencing two limb impacts per collision, theoretically reducing energy loss by half; and 3)exhibiting pseudo-elastic collisions that minimize the energy loss of redirecting the COM. These results support the suggestion that the reduction of collisional energy loss is an important consideration in gait selection during terrestrial locomotion.
