An obvious performance advantage of the shark tail morphol-ogy is the contribution of the radialis muscle to continuous thrustgeneration. While not all shark species exhibit life histories neces-sitating long distance migrations or the capture of fast-swimmingprey, they all profit from a metabolic advantage to continuousthrust production. When a fish swims, drag on the body causesdeceleration whenever it is not producing thrust. Then, when thrustis produced, momentum created must overcome the inertial massof the body in addition to providing forward propulsion. If the bodydoes not decelerate between tail beats, then the momentum con-tinuously drives the fish forward, thereby facilitating increases invelocity.