The fastest animals on our planet are neither the smallest nor the largest. The cheetah, yellowfin tuna fish and white-bellied swift, all known for their speed, share one common trait: their intermediate size. But why does this size favor speed?
A team of researchers attempted to answer this riddle by simulating human models of different sizes. Using a computer model, they were able to vary the size of the virtual human, from the size of a mouse to that of a horse, and observe the consequences on the vitesse maximum achievable.
This model, developed since the 2000s with the software OpenSimfaithfully reproduces the bones, muscles and tendons of the human body. Used in many areas of researchit allows us to study human movements and simulate the effects of surgery. In 2019, Belgian researchers pushed the simulation even further by asking this model to find the ideal muscle combinations to reach a speed datawithout human intervention.
As part of this new study, scientists varied the size of the model, from 100 grams to 2,000 kg. They discovered that the most massive models could not move, while those weighing 900 kg were close to the limits of human movement. The model reaching the highest speed weighed around 47 kg.
The key lies in the muscular strength needed to achieve high speeds. The larger the animal, the more difficult it is for its muscles to produce sufficient force to propel itself quickly. Indeed, larger muscles have a reduced cross-sectional area in relation to their mass, which limits their effectiveness.
Intermediate-sized animals, such as the cheetah, generally reach the highest speeds. Computer models of humans, scaled to sizes ranging from that of a mouse to that of a horse, reveal a similar pattern. This highlights the underlying biomechanical reasons.
Conversely, miniature models, although equipped with relatively stronger muscles, struggle to remain in contact with the ground due to their low mass. They must adopt a lower posture to generate enough force without leaving the ground, thus limiting their speed of movement. course.
Thus, this compromise between ground force and stride frequency favors an intermediate size, where the mass is perfectly balanced. For humans, this optimal size is around 47 kg.
This research suggests that evolution has already achieved a balance between speed and body mass in humans.
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