1Primate Research Institute, Kyoto University, 2Graduate School of Human Sciences, Osaka University
April 18, 2020 , Platinum Ballroom
In human walking, coordinated out-of-phase axial rotations of the thorax and pelvis is important for cancellations of angular momentum. It has long been thought that this rotational capability is a distinctive feature of humans because great apes, which have rigid and immobile trunk, seem to lack the ability of the thorax to counter axial pelvic rotations. However, Thompson et al. (2015) showed that chimpanzees also counter-rotate their thorax relative to the pelvis during bipedal walking, raising a question about the origins and development of this characteristics. In this study, we measured the axial rotation of the upper thoracic, lower thoracic, lumbar, and pelvic regions during bipedal walking in six humans, a white-handed gibbon and five Japanese macaques, to investigate if the axial rotations between thorax and pelvis are observed in non-hominid primate species. Our results showed that the thorax of the gibbon and Japanese macaques moves in phase with the pelvis, but there were as much counter rotations between the thorax and the pelvis as humans, suggesting that relative rotation is not unique to the hominid lineage, but a characteristics which is generated by mechanical requirements of bipedal walking such as the reduction of angular momentum. Given for the increased number of lumbar vertebrae in Japanese macaques and gibbons compared to chimpanzees, their lumbar region likely to have larger rotational capability. However, the total range of motion between the thorax and pelvis is similar in these three species, indicating the existence of optimum trunk rotational amount during bipedal walking.