Meeting Abstract
Many organisms use springs to actuate extremely fast movements because they can bypass the power limits of other actuators, like muscles. Measurement of muscle-mass-specific power exceeding muscle limits is a common way to identify systems actuated by springs; however, this measurement says nothing about the power of the spring itself. Here we explore the power limits of biological springs and their potential to determine the upper limits of performance in movements actuated by spring recoil. Because a spring applies force to accelerate a mass, we can predict that recoil velocity and power scale as mass-0.5 and maximum power is reached when the spring moves only its own mass. However, a spring oscillating at high frequencies releases less energy during recoil than is stored during stretching and this loss is greater at higher frequencies. This leads to the prediction that a spring moving a very light mass will recoil with high velocity, yet much of the stored elastic energy will be lost. Therefore, for any spring there is a specific load mass that balances power output with energy loss. Using a novel experimental approach, we have measured the power of elastic tissues isolated from multiple vertebrate species recoiling with displacements <1 mm and durations <1 ms to move a range of load masses. These measurements confirm the mass-dependent trade-off: recoil power is greater at smaller masses, but energy loss is minimized at larger masses. This result suggests that biological springs must be tuned for the loads they are moving to balance energy and power. Additional experiments will explore the connection between the power/load relationship of a recoiling elastic tissue and material properties, such as resilience and loss modulus.
