‘Heel-strike’ allowed early humans to walk farther at cost of high impact forces

Research Article (open access)

Snippet of layman article:

The average person takes thousands of steps each day, instinctively walking heel-to-toe. Although they hardly register them, those consistent heel-first strides are more unique to humans than previously thought and allowed early hominins to walk farther more efficiently, but at the cost of higher impact forces on bones and joints, according to a new study led by a researcher at Penn State.

The team said the findings, published today (Sept. 8) in the Proceedings of the National Academy of Sciences, shed light on an evolutionary adaptation that made early human walking more efficient, ultimately helping our ancestors to adopt hunting and gathering practices and spread across the world.

Previous research relying on descriptive data has suggested that humans share the heel-first, or heel-strike, walking style with other great apes like the closely related chimpanzee. The authors of the new study used high-speed, high-resolution video equipment and a flat runway lined with metal plates that measure impact forces to examine how chimpanzees and humans walk.

They found that chimpanzees vary their walking style, landing on the side or ball of their foot a majority of the time and landing heel-first less often when walking on two legs compared to moving on all fours. Humans, on the other hand, always land with a heel-strike. The researchers found that this walking style saves modern humans an estimated 26% to 41% of the metabolic energy it would take to walk on the ball of the foot but results in higher impact forces, which required bigger, stronger bones and joints — later adaptations that would allow early humans to cover more ground in a safe, consistent way.