YOUNG, JW*; PATEL, BA; Stony Brook University; Stony Brook University: Do differences in body mass distribution determine symmetrical gait kinematics?

Previous research and theory have suggested a predictable relationship between the cranio-caudal position of the whole-body center of mass (CM), interlimb coordination and limb kinematics during symmetrical gaits. In particular, when the CM is positioned cranially (closer to the forelimbs), lateral sequence (LS) gaits should be more stable; when the CM is positioned caudally (closer to the hindlimbs), diagonal sequence (DS) gaits should be more stable. Moreover, positioning the CM closer to one set of limbs should increase contact time and joint extension in those limbs (i.e., result in a �stiffer� gait) as a way of mitigating limb loading. We addressed these hypotheses by measuring the gait kinematics of a female patas monkey (Erythrocebus patas) wearing a weighted belt (5-12% of the animal�s body mass) strapped above the pectoral girdle � thereby shifting the position of the CM cranially � and comparing these observations to an unweighted control condition. Duty factor, limb phasing, limb yield and limb protraction angles were measured. Unlike previously studied taxa, primates are non-cursorial, primarily utilize DS footfall patterns and tend to walk with compliant gaits, making this an interesting system in which to test the hypotheses outlined above. If body mass distribution is a determinant of gait kinematics, increased cranial mass should shift interlimb phasing toward a LS gait and reduce the use of compliant forelimb kinematics. Results indicate that although added weight caused significant increases in forelimb duty factor, gait selection and limb kinematics were unaffected. These results call into question the hypothesis that differences in body mass distribution are responsible for the diversity of mammalian gait kinematics.