A new study has pinpointed principles that are common in the mechanical systems that animals, plants, fungi and machines use to maximize kinetic energy delivery. The results help explain why some animals have muscles to generate force, while others rely on spring-like systems and stored energy. Three key components of a power-generating and power-amplifying system can include a motor that inputs energy, a spring that can store energy, and a latch to trigger a sudden release. Here, Mark Ilton and colleagues used modeling to explore when these components work together efficiently - and when they don't. Their work includes a dataset of acceleration in kinetic systems of more than 100 species. Among several findings, they report that the shape of the latch influences the duration of energy release. Shorter release times yield greater power amplification, while a sufficiently long duration can completely eliminate power amplification. Of note, the authors found evidence to explain why systems that amplify power (those involving a spring), tend to be small; as it turns out, above a certain size, a spring does not enhance kinematic output and an organism is best served by using muscle. As well, muscle-based power amplification was found to have lower and upper limits in efficacy, which the authors say may explain why the smallest and largest insects tend to jump more slowly than mid-sized insects.