Gait and EMGs during bipedal walk of a gibbon (<i>Hylobates agilis</i>) on flat surface

Abstract

An experimental analysis was performed on bipedal walking of a gibbon (Hylobates agilis) on flat substrate. Kinematic observation revealed that bipedal walk of the gibbon was characterized with bouncing strides, which occasionally turned daring by pushing off with the propulsive limb and 'pseudo' hyper-extension of the hip caused by the pelvic rotation and an abduction of the hip joint. EMGs indicated that the back muscles, hip and knee extensors, and plantar-flexor of the ankle were acting almost in a synchrony from the touch-down to the late mid-stance phase of the limb concerned, thus in a basically different manner from the human walking. While the vastus lateralis did not show a gradual increase of its activity toward the late mid-stance phase seen in the other nonhuman primates, the gastroc-nemius did so. This feature of the gastrocnemius was more remarkable in fast walk than in slow walk, implying its positive role in the bouncing propulsion of the gibbon.