The ideal body weight for running fast
Compared to other animals, humans are quite slow when travelling. However, in relation to their physique, they get the best out of it, as an analysis of weight and speed shows.
The fastest land animal in the world is the cheetah. It can reach more than 100 kilometres per hour when running - something humans can only dream of. But anyone who is annoyed at the thought of not being able to outrun the spotted hunter in an emergency may be comforted by this realisation: in relation to our physique, we humans have achieved almost the optimum speed, at least on average. If we were significantly smaller and lighter or noticeably taller and heavier, we would move much more slowly. This is what a research team led by Christofer J. Clemente from the University of Queensland in Australia has determined in extensive studies and published in the scientific journal "Nature Communications"
For their studies, the scientists used simulation software based on a publicly available model of the human body. Muscles, bones and tendons are modelled in great detail. The software developed in 2019 can, for example, show how the individual components behave when running at different speeds. Clemente's team created human models of various sizes - from small, 100-gram dwarves to 2000-kilogram giants. They then had the programme simulate the maximum speed at which the different sized specimens could move.
The giants weighing several tonnes lost the virtual race because they didn't even get off the ground. It was only possible to move on two legs with a human physique up to a weight of around 900 kilograms. But even being small only had a limited advantage: the miniature humans weighing 100 grams were also unable to move. If you plot speed against body weight, you get a curve with an optimal body weight of 47 kilograms.
The authors also suggest an explanation as to why this might be the case. According to further findings, how fast someone can run depends mainly on the force with which the person pushes themselves off the ground - in other words, not how fast they can move their legs. The force that can be exerted in turn depends on the muscles, or more precisely on their cross-sectional area. However, this does not increase as quickly as the mass of the muscles with increasing body size, and accordingly the muscles are relatively weaker above a certain body size. In contrast, the muscles of very light miniature people are relatively strong, but they are too light to exert sufficient force on the ground and push themselves off.
To be able to run fast, you must therefore be neither too big nor too small - like the cheetah, which also weighs 47 kilograms on average. The average human adult weight is around 62 kilograms. This is relatively close to the optimum, as the authors note. They speculate that the ability to run fast was an evolutionary advantage. Other hominins were significantly heavier or lighter than modern humans, such as Australopithecus afarensis, which weighed an average of 30 kilograms, or Homo erectus, which was significantly heavier at an average of 80 kilograms.
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