Invertebrate swimming: integrating internal and external mechanics.

Challenges in understanding design for locomotion in any swimming animal revolve around the complex interactions between the mechanics of fluid motions around an animal and the mechanics of internal force production. The former is governed by force-velocity relationships that arise from fluid motion, whereas the latter is governed by force-velocity relationships of both active (e.g. muscle) and passive tissues. In reality, all such relationships must be satisfied simultaneously in any swimming creature. Towards this end, I combine traditional analyses of muscle contractility, soft tissue mechanics and hydrodynamic models to examine how organism morphology, muscle physiology and mode of propulsion interact to affect swimming performance. This combination involves a solution to a set of equations that describe the relevant internal and external mechanics. The solution has the unique benefit of providing predictions for both body and propulsor kinematics. Such predictions are examined for a variety swimming animals and are compared with existing kinematic data. Armed with such an approach, I re-examine traditional scaling arguments to show that classical approaches that neglect internal mechanics predict swimming performance relationships that may not be physiologically feasible.