The variation in the arrangement of muscles across animals is thought to have evolved to allow muscle to power the broad range of movements observed in nature, and to perform optimally while doing so. In a recently published paper, Professor Emanuel Azizi and Dr. Natalie C. Holt, Ecology and Evolutionary Biology, investigated whether skeletal muscle morphology and physiology enables optimal performance during locomotion. Using the cane toad plantaris muscle as their experimental model, they found that velocity always occurs at optimal speed during movement, while optimal length only occurs when demand is at its peak. Their results show that animals are not always able to use muscle optimally across all movements, but instead tune their behavior to allow optimal muscle performance when demand is greatest. The study reveals the conditions that shape the structure-function relationship in skeletal muscle.