Why even the fastest human can’t outrun your house cat
This weekend, the the fastest sprinters on the planet gathered at the Tokyo Olympics to compete for the gold in the 100 meters. Lamont Marcell Jacobs crossed the finish line in 9.80 seconds to bring Italy their first gold in the event. In the women’s race, Jamaica won gold, silver and bronze, a clear sweep led by Elaine Thompson-Herah, who broke a 33-year-old women’s Olympic record with a time of 10.61 seconds.
But none of them could touch the legacy of Jamaica’s eight-time Olympic gold medalist Usain Bolt, who retired in 2017 but still holds the title of world’s fastest man. . Bolt ran the 100 meters in 9.58 seconds. Max at around 27 miles per hour, that’s just below the top speed of a house cat. (Yes, a house cat.) In a race against cheetahs and antelopes, the world’s fastest animals, Bolt wouldn’t stand a chance.
You might think that how fast an animal can go depends on the size of its muscles: more strength, more speed. While this is true to some extent, an elephant will never overtake a gazelle. So what really determines top speed?
Recently, a group of scientists led by biomechanist Michael Günther, then affiliated with the University of Stuttgart, set out to determine the laws of nature that govern maximum running speeds in the animal kingdom. In a new study published last week in the Journal of Theoretical Biology, they present a complex model taking into account height, leg length, muscle density, etc. to find out which body design elements are most important for optimizing speed.
This research provides insight into the biological evolution of legged animals and their corresponding gaits, and it could be used by environmentalists to understand how speed constraints on animal movements inform population, habitat selection and community dynamics in different species. For roboticists and biomedical engineers, learning nature’s optimal body structures for speed could further improve the design of bipedal walking machines and prostheses.
“It’s about understanding the reasons for evolution, and why and how it shapes the body,” Günther explains of the goal of the project. “If you ask this question in a mechanical way, you can really better understand how body design is shaped by changing demands, for example, being fast. “
Previous work in this area, led by Myriam Hirt of the German Center for Integrative Biodiversity Research, found that the key to speed had to do with an animal’s metabolism, the process by which the body converts nutrients into fuel, a finite amount of which is stored in muscle fibers for use when sprinting. Hirt’s team found that larger animals run out of this fuel faster than smaller animals because it takes them longer to speed up their heavier bodies. This is called muscle fatigue. This explains why, theoretically, a human could have outrun a Tyrannosaurus rex.
But Günther and his colleagues were skeptical. “I thought maybe we could give another explanation,” he said, an explanation that only used the principles of classical physics to explain the speed constraints. They therefore built a biomechanical model made up of over 40 different parameters relating to body design, stroke geometry and the balance of competing forces acting on the body.
“The basic idea is that two things limit the maximum speed,” says Robert Rockenfeller, mathematician at the University of Koblenz-Landau, co-author of the study. The first is air resistance, or drag, the opposing force acting on each leg as it tries to push the body forward. Since the effects of drag do not increase with mass, it is the dominant factor in limiting speed in small animals. “If you were infinitely heavy, you would run infinitely fast, depending on the drag of the air,” says Rockenfeller.