Why even the fastest man in the world can't outrun a regular domestic cat

Why even the fastest man in the world can't outrun a regular domestic cat
Why even the fastest man in the world can't outrun a regular domestic cat

Even the fastest human on the planet will not be able to catch up with the average house cat, according to a new study. In a competition with cheetahs, the swift Olympian would have had no chance of winning. What determines the maximum speed?

The new model explains how different forces and body structures limit the maximum running speed in humans.

Last week, the world's fastest sprinters gathered at the Tokyo Olympics to compete for gold in the 100-meter race. Lamont Marcell Jacobs reached the finish line in 9, 80 seconds, winning Italy's first gold in this discipline. Among women, Jamaica took gold, silver and bronze - a clear victory led by Elaine Thompson-Herah, who broke the Olympic record set 33 years ago, running the distance in 10.61 seconds.

But none of them can reach the heights of the legacy of eight-time Olympic champion Usain Bolt, who retired from the sport in 2017 but still holds the title of the fastest man on the planet. Bolt ran the 100m in 9.58 seconds. However, although Bolt's speed reached 43.5 kilometers per hour, this is still less than the speed of a normal domestic cat. (Yes, the common domestic cat.) In a competition with cheetahs and pronghorns, which are considered the fastest animals on the planet, Bolt would have no chance of winning.

You might think that how fast an animal can run 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 actually determines the top speed?

Recently, a group of scientists led by biomechanist Michael Günther from the University of Stuttgart decided to find out what laws of nature determine the maximum running speed in the animal kingdom. In their new study, the results of which were published last week in the Journal of Theoretical Biology, they presented a complex model, taking into account body size, leg length, muscle density, and more, to explain which features of the body structure are the most important to ensure the fastest possible speed.

This new study provides insight into the biological evolution of quadrupeds and their running habits, and can be used by ecologists to understand how speed limits affect populations, habitat choices, and the dynamics of populations of different species. The research could also be useful for robotics and biomedical engineers who are studying optimal animal body structures to improve designs for bipedal walking robots and various prostheses.

“It's about understanding the causes of evolution, as well as why and how it changes body structure,” Gunther said of the purpose of the study. "You can also expand your knowledge of how various evolutionary needs affect body composition, including the need to run fast."

Previous research in this area, led by Myriam Hirt of the German Center for Integrative Biodiversity Research, has shown that the key to speed has to do with animal metabolism - the process of converting nutrients into fuel., a finite amount of which is stored in muscle fibers for use in running.Hurt's team found that larger animals run out of fuel faster than smaller ones because they take longer to accelerate their heavier bodies. This is called muscle fatigue. This explains why - purely in theory - a human could outrun a Tyrannosaurus.

But Gunther and his colleagues were skeptical about this conclusion. “I thought we could give another explanation,” he said, “an explanation where only the principles of classical physics would be used to characterize the speed limits. Therefore, scientists have created a biomechanical model consisting of more than 40 different parameters related to body structure, running geometry and the balance of forces acting on the body.

“The basic idea is that there are two factors limiting the top speed,” says Robert Rockenfeller, a mathematician at the University of Koblenz-Landau who co-authored the study. The first is air resistance, which is the force acting on each leg as it tries to move the body forward. Since the impact of the drag force does not increase with increasing mass, it is this that is the dominant speed limiting factor in smaller animals. “Given the force of air resistance, if you were infinitely heavy, you would run infinitely fast,” explained Rockenfeller.

The second acting factor, which just increases with an increase in body weight, is inertia, that is, the body's resistance to a change in its state, in this case, when accelerating from a state of rest. Rockenfeller says that an animal has a time limit for accelerating its own mass: this is the time interval between when the foot is on the ground until the moment the foot is lifted off the ground. This is especially limiting for larger animals: the more mass that needs to be propelled forward, the more difficult it is to overcome the momentum. Thus, animals with a lower body weight have an advantage.

According to the study, the optimal body weight to overcome air resistance and inertia is about 50 kilograms. It is no coincidence that this is the average weight of cheetahs and pronghorns.

Gunther's team was also able to calculate the theoretical maximum speed for various body structures weighing about 100 kg. A domestic cat of this size could run at a speed of 74 kilometers per hour; a giant spider, if its legs could somehow support its weight, would accelerate to 56 kilometers per hour. It is not surprising, but the average indicator for a person weighing 100 kilograms is the last in this row: his speed will not exceed 38 kilometers per hour.

But body size is not the only feature that affects top speed. The model showed that leg length matters too. Animals with longer legs can push their body further forward before their foot has to lift off the ground, which prolongs the time it takes them to accelerate between the mid-leg phase and the lift off the ground.

Regarding why four-legged animals can run faster than humans, Gunther explained that this is not because we only have two legs, but because our body is upright and experiences the full force of gravity. In the process of evolution in bipedal creatures, the spine became much less mobile, because for them balance and stability were priority of speed. Meanwhile, animals whose bodies are located parallel to the ground, in the process of evolution received more flexible spines, which are optimal for prolonged contact of the foot with the ground.

What about muscle fatigue? "It doesn't matter," Gunther says. As part of their research, his team concluded that any animal can accelerate to at least 90% of its maximum speed before it runs out of fuel.

Carl Cloyed, an ecologist at the Dauphin Island Sea Lab in Alabama who studies animal locomotion, believes that from an evolutionary perspective, a biomechanical explanation makes more sense than the muscle that runs out of fuel. … “I would suggest that in the process of evolution, animals had to adapt to this,” he said. However, he did acknowledge that more experimental research is needed to validate the new model.

Gunther and Rockenfeller agree that more experiments are needed to test their findings, and they believe they have provided a comprehensive model for other scientists to continue testing. However, all scientists recognize that this will be fraught with difficulties. Scientists will need to capture and observe animals in the laboratory, or use high-quality video footage to analyze the biomechanics of their movements, Kloyed said. The most accurate method for studying the movements of a running animal may be the implantation of mechanical sensors into their muscle tissue and further observation of them in their natural habitat. But, according to Gunther, this entails a host of obvious logistical and ethical issues.

Kloyed also wants to see how this analysis expands, especially to cover other modes of locomotion, such as flying and swimming. "If this hypothesis turns out to be correct, it can be applied to other objects in the environment."

So, can anyone beat Usain Bolt's record? Perhaps, but people are unlikely to be able to run even faster. The biomechanics of running shows that we are already approaching the limits of the human body. And when someone else becomes the fastest person on the planet, he will have to agree that he will only wear this title among people. In the animal kingdom, we have nothing to count on.

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