Heel striking saved energy while increasing impact loading
In human and chimpanzee walking experiments, heel-first steps used less energy but produced higher impact loading; the inference about fossil hominins remains indirect.
Science··Morning
Humans landed on the heel more consistently
Researchers compared the walking of 12 humans and three chimpanzees using high-speed imaging and a force-measuring runway, and also incorporated chimpanzee data collected by other teams. The human participants consistently began their steps with the heel. Chimpanzees more often landed on the side or front of the foot while walking on two legs and used more variable contact patterns even during quadrupedal walking. Phys.org and DongA Science report this cross-species difference from the same PNAS study in separate accounts.[1], [2]
The energy saving came with a harder impact
In the human experiments, midfoot walking required 26% to 41% more metabolic energy than heel striking. In return, a heel strike produced a faster and larger impact load. The same mechanical trade-off appeared in chimpanzees: heel contact increased loading rates relative to midfoot contact. The result does not show that heel-first walking is better under every condition; the pattern that lowers energy cost also creates more abrupt forces on bones and joints.[1], [2]
The evolutionary explanation is an indirect inference
The authors propose that thicker heel bones and larger knee and ankle joints may have helped absorb high impact forces safely. Such an adaptation could have saved energy during long-distance hunting and gathering. But the experiment did not directly measure the gait of fossil hominins; it draws an interpretation about the past from biomechanics in modern humans and chimpanzees. The study also did not test whether hard modern surfaces alter this balance, and the findings do not provide a reason to avoid ordinary walking.[1], [2]
