Humans got rid of rotating hips to take a shorter stride than chimpanzees

Humans got rid of rotating hips to take a shorter stride than chimpanzees

Humans were thought to have the longest strides of primates for their height, but now researchers have found that chimpanzees take 25% more strides than we do, thanks to their rotating hips, which rotate up to 61 degrees each time. they take a step to compensate for their crouched posture and shorter legs.

According to Nathan Thompson, from the New York Institute of Technology (United States), “standardized by their size, humans do not have long strides.”

However, until recently, most scientists believed that the human stride was relatively long to be efficient; “This is taught in almost every introductory class and in textbooks,” recalls Thompson, explaining that the misconception only became really apparent when he began delving into the literature.

When Thompson began to investigate the extent to which chimps rotate their pelvis when walking, he began to wonder if turning their hips might be the key to chimpanzees’ longer strides.

Intrigued by this possibility, he decided to compare chimpanzees and humans walking at different speeds and now publishes in the ‘Journal of Experimental Biology’ his discovery that chimpanzees’ strides are 25% longer than ours for their height thanks to their rotating hips, which lengthen their strides 5.4 times more than the mini-movements humans make when walking.

“Working with people and animals always has its difficulties,” acknowledges Thompson, who spent several years with Brigitte Demes, Susan Larson (both at Stony Brook University) and Matthew O’Neill (Midwestern University) familiarizing chimpanzees with the They walked upright on two feet while filming the animals in 3D.

Once Danielle Rubinstein, William Parrella-O’Donnell, and Matt Brett reconstructed the human stride pattern and hip movement in 3D, the team scaled humans down to the size of chimpanzees and found that although human legs were proportionally 112% longer, their strides were 26.7% shorter.

Meanwhile, chimpanzees rotated their hips between 28 and 61 degrees, in contrast to humans, who barely twisted their pelvis, by only about 8 degrees.

And when the team saw how far their pelvic rotation advanced in terms of stride length, the chimps had a clear advantage. Their rotating hips lengthened their stride 5.4 times longer, relative to their size, than the tiny spin of humans.

“I think chimps use pelvic rotations to try to squeeze the full length of their stride, otherwise their strides would be very small,” says Thompson, who explains that apes and monkeys tend to walk with their legs bent, which which naturally shortens your stride – I don’t think there are many options other than pelvic rotation, given its anatomical limitations.”

But when asked why humans have given up turning their hips when they could extend their strides, Thompson suggests a possibility: that extreme hip rotations could cancel out the natural sway of our arms and legs – which are counterbalanced between yes – which would force our muscles to work harder and make walking less efficient, a price that simply wouldn’t be worth paying for a longer stride length.

Thompson also explains that scientists had thought for decades that humans had developed the longest stride possible to be more efficient, but now that it turns out that our stride is considerably shorter than that of our closest cousins, he suspects that other factors have played a role. a bigger impact on the way we walk.

“Humans have had about 7 million years of selective pressure for economic bipedalism; this means that there has been a lot of time to experiment with the costs and benefits, so it might be worth walking with slightly shorter strides, because any energy that we lose, we could recover it elsewhere,” he suggests.

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