A general law for animal locomotion?

The propulsion system of animals that fly or swim are quite different from each other in their morphology and function, yet the propulsive efficiency could be maximized by a surprising similarity in the fine tuning of flapping frequency, amplitude and forward speed, according to a new study by Taylor et al. This conclusion was based on an analysis of the Strouhal number, which is a dynamic similarity index relevant to propulsion that relies on vortex shedding for thrust generation. Such fine-tuning of the propulsive system suggests possible consequences for physiological and ecological adaptations related to, for example muscle operating frequency and optimal speed of muscle contraction.