Dynamic Plantar Pressure Distribution during Locomotion in Japanese Macaques (Macaca fuscata)

Hirasaki, E., Higurashi, Y. & Kumakura, H.

日常的に四足で歩く種が二足歩行を行った時、彼らの足の動きは四足歩行時と比べてどのように変化するのだろうか。ヒトの足の形と動きを進化的な文脈でよりよく理解するための一助として、本研究では、ニホンザルが自然な速度で二足歩行する際の足底圧を計測し、四足歩行時のものと比較した。足底を９つの領域に分け、それぞれの領域の圧分布とその経時変化を120Hzで記録した。計測には圧力分布計測装置（Big-mat 1/4、ニッタ社）を用いた。その結果、二足歩行と四足歩行では、拇趾の使い方、圧中心の軌跡、圧の大きさの経時変化などに大きな違いがあり、二足歩行時の計測結果に見られる特徴のいくつかは、ヒトの直立二足歩行に見られる足底圧の特徴との類似性を示した。中でも、立脚後期に見られた圧中心の内側への偏移は、二足歩行の生機構学的要求によるものと考えられる。一方で、ニホンザルの二足歩行には、踵が接地しない、土踏まずが存在しない、拇趾が大きく外転している、機能軸が第３趾を通るといった、ヒト歩行とは大きく異なり四足歩行と共通する特徴も観察された。

American Journal of Physical Anthropology 142 (1): 149–156

To better place the form and motion of the human foot in an evolutionary context, understanding how foot motions change when quadrupeds walk bipedally can be informative. For this purpose, we compared the pressures beneath the foot during bipedal and quadrupedal walking in Japanese macaques (Macaca fuscata). The pressure at nine plantar regions was recorded using a pressure mat (120 Hz), while the animals walked on a level walkway at their preferred speeds. The results revealed substantial differences in foot use between the two modes of locomotion, and some features observed during bipedal walking resembled human gait, such as the medial transfer of the center of pressure (COP), abrupt declines in forefoot pressures, and the increased pressure beneath the hallux, all occurring during the late-stance phase. In particular, the medial transfer of the COP, which is also observed in bonobos (Vereecke et al.: Am J Phys Anthropol 120 (2003) 373–383), was due to a biomechanical requirement for a hind limb dominant gait, such as bipedal walking. Features shared by bipedal and quadrupedal locomotion that were quite different from human locomotion were also observed: the heel never contacted the ground, a foot longitudinal arch was absent, the hallux was widely abducted, and the functional axis was on the third digit, not the second.

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