Rapid Power and Energy Release from Elastic Network Polymers

Elastic biological springs are used by animals in their locomotion primarily for either power amplification or energy conservation. Power amplification, for motions like a frog jump or a mantis shrimp punch, is achieved with asymmetrical loading rates, where energy is slowly loaded into a biological spring and rapidly released. In contrast, energy-conserving movements such as running typically show symmetric loading/unloading patterns and involve a cyclic flow of energy to/from the spring. In this work, we use numerical simulations and experimental measurements to explore the roles of mechanical properties and loading rates in both of these elastically-driven movements. We focus on two metrics relevant to elastic movements in biology: maximum power output and resilience (the fraction of total stored elastic energy that is released as useful mechanical work). We find trade-offs between resilience and maximum power output/loading rate symmetry; energy loss increases with higher maximum power and asymmetry between the rates. These results suggest that spring material properties might contribute to biologically relevant trade-offs in animal locomotion.