The energetic cost of adaptive feet in walking

Abstract

While humanoid feet are made of rigid plates,
human feet have evolved into highly articulated and flexible
elements. This adaptiveness provides key advantages. It absorbs
impacts and secures grip when interacting with the environment. However, the human foot design potentially increases
the energetic cost, because it features actuators and provides
less power transfer than a rigid plate does. Here we use
neuromuscular models with different foot designs and show
that human feet incur about 20% more energetic cost than
rigid ones for walking speeds up to 1.2ms−1 , which is close to
the preferred walking speed. Above this speed, human feet do
not show an energetic disadvantage. In addition we propose
a foot design for prosthetic or humanoid feet which preserves
key features of adaptive feet but does not require actuation,
and show that it reduces the energetic cost by 15% or more
independent of the walking speed. We conclude that human
evolution may have traded the advantages of adaptive feet for
energy efficiency, and that robotic systems could gain the former
without compromising on the latter.