This weekend, the fastest sprinters on the planet gathered at Tokyo Olympics to compete for gold in the 100-meter dash. Lamont Marcell Jacobs crossed the finish line in 9.80 seconds and brought Italy his first gold in the competition. In the women’s race, Jamaica won gold, silver and a bronze-clean move led by Elaine Thompson-Herah, who broke the 33-year-old Olympic women’s record with 10.61 seconds.
But none of them could touch the legacy of eight-time Jamaican Olympic gold medalist Usain Bolt, who retired in 2017 but can still boast the title of the fastest man in the world. Bolt ran 100 meters in 9.58 seconds. At a maximum speed of about 27 miles per hour, it is below the maximum speed of a domestic cat. (Yes, a domestic cat.) In a race against cheetahs and horns, the fastest animals in the world, Bolt would have no chance.
You might think that the speed of an animal can go depends on the size of the muscles: higher strength, higher speed. While this is true to some extent, the elephant will never surpass the gazelle. So what really determines top speed?
Recently, a group of scientists led by biomechanic Michael Günther, then affiliated with the University of Stuttgart, set out to establish natural laws governing maximum running speeds in the animal kingdom. U new study published last week in Journal of Theoretical Biology, represent a complex model that takes into account size, leg length, muscle density and more to discover which body design elements are most important for speed optimization.
This research provides insight into the biological evolution of animals with legs and their proper gait, and ecologists could use it to understand how animal movement speed limitations affect population, habitat selection, and community dynamics in different species. For robotics and biomedical engineers, learning about the optimal velocity structures of nature could further improve design two-legged walking machines i prosthetics.
“It’s about understanding the reasons for evolution, and why and how it shapes the body,” says Günther of the project’s goal. “If you ask this question mechanically, then you can really add an understanding of how body design is shaped by evolutionary requirements – for example, being fast.”
Earlier works in this area, led by Myriam Hirt of the German Center for Integrative Biodiversity Research, found that the key to speed is linked to the animal’s metabolism, the process by which the body converts nutrients into fuel, the final amount of which is stored in muscle fibers for use in sprinting. Hirt’s team found that larger animals run out of this fuel faster than smaller animals because they need more time to accelerate their heavier bodies. This is known as muscle fatigue. It explains why a theoretical man could have overtook Tyrannosaurus rex.
But Günther and his colleagues were skeptical. “I thought we could give another explanation,” he says, who used only the principles of classical physics to explain speed limits. Thus, they built a biomechanical model consisting of over 40 different parameters related to body design, running geometry and balance of competing forces acting on the body.
“The basic idea is that two things limit the maximum speed,” says Robert Rockenfeller, a mathematician at the University of Koblenz-Landau who co-authored the study. The first is air resistance or resistance, the opposite force acting on each leg as it tries to push the body forward. Since the effects of resistance do not increase with mass, it is the dominant factor limiting the rate of restriction in smaller animals. “If you were infinitely heavy, you would run infinitely fast, in line with air resistance,” says Rockenfeller.