Adrian Bejan | Energy store & release motion, from Design in Nature

Sep 11, 2025

The video explores the concept of store-and-release energy locomotion, demonstrating how certain animals achieve extraordinary jumps by compressing elastic structures that function like springs. Unlike continuous movers such as runners, swimmers, or flyers, these jumpers concentrate energy and then release it suddenly, creating motion far beyond what body size alone would predict. The explanation clarifies why insects like fleas and grasshoppers seem to defy scaling laws, while also extending the analysis to aquatic creatures and larger jumpers, demonstrating that the same mechanics apply across environments with different outcomes.

The cheetah appears as an outlier in speed–size scaling. Still, when considering its lifestyle, spending most of its time resting or watching, it falls back in line with theoretical expectations. This shows that what looks like deviation is often due to context, not contradiction, and highlights how purpose and behavior shape locomotion patterns.
Fleas, grasshoppers, and similar animals use an elastic organ that stores spring energy before release. When the latch is freed, the stored energy propels the body upward or forward, converting stored potential into kinetic energy. This explains why their jumps can cover distances many times their body length, a result of density ratios and spring mechanics rather than simple muscle force.
The theory considers drag and ambient density, showing that in air, the low density allows insects to leap far. In contrast, in water, the high density constrains aquatic jumpers like spiny lobsters to distances on the order of their body length. This contrast underlines how the same design principle yields different results depending on the medium.
When Reynolds numbers are high, drag coefficients remain constant, but at low Reynolds numbers, such as for very small creatures like fleas, drag depends on velocity and viscosity. Even so, the analysis still leads to predictable relationships between body size, density, and jump distance, demonstrating the robustness of the framework.
The same logic extends to larger jumpers such as frogs, kangaroos, and even basketball players. In these cases, gravitational potential energy sets the limit: the stored spring energy translates into vertical height rather than just horizontal displacement. Whether in insects, crustaceans, or humans, the principle remains: locomotion by jumping is governed by the storage and sudden release of elastic energy.

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