Meeting Abstract
25.7 Saturday, Jan. 4 15:00 Chimpanzee Bipedal Gait Mechanics and Early Hominin Gait Evolution DEMES, B.*; O’NEILL, M.C.; THOMPSON, N.E.; Stony Brook University; Stony Brook University; Stony Brook University brigitte.demes@stonybrook.edu
Humans share a last common ancestor with chimpanzees. One of the features that set humans apart from chimpanzees is our habitual bipedal locomotor mode and the use of an extended-limb posture. Chimpanzees, in contrast, are quadrupeds that engage in facultative bipedalism using a flexed-limb posture. As terrestrial bipedalism evolved early in the hominin lineage and early hominins were ape-like in many aspects of their postcranial anatomy, chimpanzees provide a useful extant model for the bipedal gait of some of our earliest ancestors. In this study, we present a comprehensive data set on the center of mass (CoM) mechanics of chimpanzee bipedalism. Three-dimensional ground reaction force recordings of > 100 strides of three male chimpanzees (27.3±5.1kg) served as the basis for calculating CoM mechanical energy fluctuations. Chimpanzees use a bipedal walking gait, with duty factors > 0.5 and Froude numbers < 0.5. Exchanges between CoM kinetic and potential energies – a hallmark of human walking – are low to moderate (5-50%). They are lower than for quadrupedal walking recorded in the same subjects, and they are also low in comparison to human bipedal walking. Mediolateral body sway is pronounced in chimpanzee bipedalism. It has a negative effect on energy exchanges that are 5-10% higher without mediolateral kinetic energy being considered. Mediolateral sway in chimpanzee bipedalism therefore requires more mechanical work on the CoM. Chimpanzees resemble several other nonhuman primates studied to date in having compliant bipedal gaits with moderate energy exchanges. Human walking, on the other hand, is more similar to the walking gaits of many nonprimate terrestrial animals, using inverted-pendulum swings on extended limbs and having high mechanical energy recoveries. Supported by NSF BCS 0935321.
