DEVELOPMENT OF QUADRUPEDAL WALKING IN HUMAN BEINGS

It is known that nonhuman primates differ from most nonprimate mammals in the predominant use of the forward cross type locomotion, as opposed to the backward cross type, while walking. In this study, we investigated the development of the sequence of movenent of the four limbs, both on and off the ground, and the effect of weight load on it. We also tried to account for the sequence of movenent of the four limbs in human quadrupedal walking. Through the comparative study of animal and human quadrupedal walking, we clarified the functions of fore and hind limbs during quadrupedal walking, and the evolution of locomotion. The subjects were 15 infants under one year old, 90 children aged from 1 to 5 years, and 20 adults. We observed two kinds of quadrupedal locomotion: "creeping on hands and knees" and "walking on hands and feet". The children over 3 years of age and the adults were requested to perform these two kinds of locomotion on a downward slope (15°), which would necessitate the support of the body by the forelimbs more than on level ground. Body weight was measured on each of the fore and hind limbs while the subjects assumed various postures. Cinematograms were recorded on VTR. The sequence of movement of the four limbs was determined after repeated viewings of the VTR. We found that on a flat surface the bb-pattern (the backward cross type of limb movement that takes place both on and off the ground) was obvious in the creeping of infants and in the walking of subjects of all ages. The fb-pattern (the sequence of limb movement characterized by the forward cross type of locomotion off the ground and the backward cross type on the ground) was also observed in the creeping of children and adults. In walking, the body weight fell more heavily on the forelimbs than on the hindlimbs in static standing posture, especially in the creeping of children and adults. On the slope, twice as many children showed the bb-pattern while creeping than displayed it on the level ground. From these results, the following can be concluded concerning the movement of the four limbs in human beings. Humans, by nature, possess the motor program for the backward cross type of locomotion. In the pre-bipedal period, fore and hind limbs seem to have the same function. However, after humans master bipedal walking, the function of limbs in creeping may differentiate: forelimbs function to orient, and hindlimbs are for propulsion. However, this functional division between the fore and hind limbs is not apparent in those subjects walking on hands and feet after the achievement of bipedal walking. There may be an evolutionary continuum between walking on hands and feet in human beings and the quadrupedal walking of nonprimate mammals.