Humans consistently walk heel-first, a unique walking style that saves energy but creates higher impact forces on bones and joints.<\/p>\n
Walking is so familiar that the first moment of each step rarely gets much attention. <\/p>\n
Humans<\/a> normally place the heel down first and roll forward across the foot, a simple movement that helps make walking economical.<\/p>\n That matters because changing where the foot lands changed how much energy people used. <\/p>\n The finding may also help explain how human ancestors became better suited for traveling farther on two legs.<\/p>\n The first moment of each step<\/p>\n Nicholas Holowka, an assistant professor of anthropology at The Pennsylvania State University<\/a>, led the comparison of human and chimpanzee walking.<\/p>\n \u201cWhen people think about what makes human walking unique, they talk about upright walking \u2013 our backs are straight and our legs are extended,\u201d said Holowka. <\/p>\n \u201cWhat we\u2019re saying in this article is that landing on our heel is a unique aspect of human walking that\u2019s maybe been underappreciated.\u201d<\/p>\n \u201cThis study presents the best measurable comparison of humans to our closest living relatives<\/a>, chimpanzees, which shows that what we\u2019re doing when we land is distinctive in key ways.\u201d<\/p>\n Three male chimpanzees walked along a 36-foot (11-meter) path, sometimes on two legs and sometimes on all fours. <\/p>\n High-speed cameras recorded how they moved, while special plates in the floor measured the force of each step.<\/p>\n Chimpanzees land in different ways<\/p>\n The chimpanzees did not use one consistent landing style. <\/p>\n One heel-struck in 31 of 76 strides, another never heel-struck in 43 strides, and the third heel-struck in 17 of 29 strides.<\/p>\n The team measured the angle of each foot as it reached the ground. Within individual chimpanzees, the range was 2.4 to 8.6 times greater than the average range within individual humans.<\/p>\n Nine adults also walked barefoot across the runway, and all 89 of their normal steps began with the heel. Their foot angles stayed within a much narrower range.<\/p>\n Softer landings reduce rapid force<\/p>\n Chimpanzees used heel-strikes less often on two legs than on all fours. <\/p>\n Nathan Thompson, an associate professor at the New York Institute of Technology College of Osteopathic Medicine<\/a>, described why a different landing can feel softer.<\/p>\n \u201cImagine you are trying to sneak across a creaky wooden floor,\u201d said Thompson. \u201cYou tend to walk on the balls of your feet, because this reduces the rate of loading on the floor and creates less creaking. It\u2019s a softer way to walk.\u201d<\/p>\n \u201cIt seems that when walking on two legs, chimpanzees prefer the \u2018softer\u2019 way to land on their feet.\u201d<\/p>\n When chimpanzees walked on two legs, landing on the heel made force build up 57.9% to 138.1% faster than landing on the middle of the foot. <\/p>\n This means heel-first steps created a much sharper impact.<\/p>\n Heel-first walking can save energy<\/p>\n The human<\/a> experiment showed why a harder heel-first landing may still be useful. <\/p>\n Eleven participants completed the reported comparison using normal heel-strikes and a midfoot-first style, where the front outer foot touched down before the heel.<\/p>\n They walked at about 2.8 miles per hour (1.25 meters per second) while a portable breathing system measured oxygen use and carbon dioxide production. <\/p>\n These measurements showed how much energy each walking style required.<\/p>\n Walking on the middle of the foot used 26.1% to 40.8% more energy than landing on the heel. <\/p>\n However, heel-first steps created a much stronger and faster impact, with early impact forces 168% to 206% higher and loading rates 121% to 162% higher.<\/p>\n Human bones handle harder landings<\/p>\n Saving energy could make longer daily travel easier, but harder heel landings also place greater demands on the body.<\/p>\n \u201cIt seems like humans needed to evolve anatomical adaptations \u2013 thicker heel bones and bigger knee and ankle joints \u2013 to cope with these high forces,\u201d said Holowka. <\/p>\n \u201cWe think that the heel-strike played a role in enabling key human<\/a> behaviors, such as using hunting and gathering strategies that require people to walk really long distances every day to get food, but for a big payoff in food resources.\u201d<\/p>\n The paper suggests that bigger joints in the legs and wider heel bones helped spread out the force from each step. <\/p>\n This may have helped humans walk efficiently while better tolerating the higher forces.<\/p>\n Early humans faced a compromise<\/p>\n The experiments cannot reveal exactly how extinct human relatives placed their feet, so this evolutionary picture<\/a> remains an interpretation. <\/p>\n The results suggest that early upright walkers may have faced a balance between reducing impact and saving energy.<\/p>\n A midfoot-first landing could have reduced rapid loading but made walking more expensive. A heel-first landing could have saved energy but required bones and joints better suited to repeated impacts.<\/p>\n The authors suggest that anatomy suited to safe, economical heel-striking was probably present by Homo erectus. Fossils cannot show the exact landing pattern used by every extinct species.<\/p>\n The results have important limits<\/p>\n The main chimpanzee experiment included only three animals, all male and relatively young. Other chimpanzee data showed similar variation, but larger samples are needed.<\/p>\n The human groups were small too, and participants practiced the unfamiliar midfoot style for at least 10 minutes. The experiment cannot show what would happen after months or years of walking that way.<\/p>\n The researchers also did not measure injuries or damage to joint cartilage, the smooth tissue covering the ends of bones. <\/p>\n Higher loading rates therefore do not mean that normal heel-striking harms healthy modern humans<\/a>.<\/p>\n Walking still suits modern humans<\/p>\n \u201cWe humans have evolved to use this high-impact walking style in a way that is safe and natural for us,\u201d said Holowka. <\/p>\n \u201cThe novel environments that we currently live in with their hard, paved surfaces might upset the evolutionary balance in some ways. It\u2019s something that we\u2019d be interested in looking at in future research.\u201d<\/p>\n \u201cStill, walking a lot is a very healthy exercise and, although high impact, our bodies evolved to cope with it, so we shouldn\u2019t avoid it.\u201d<\/p>\n Something as ordinary as where the foot lands can change both energy use and the forces entering the leg. <\/p>\n Human walking may feel simple today because the body is well suited to this energy-saving, high-impact style.<\/p>\n The study is published in the journal Proceedings of the National Academy of Sciences<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? 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