Swimmers, I mean top level swimmers, have never agreed about which of two arm movements is most efficient for freestyle swimming. In one corner, we have proponents of the paddle stroke, also known as the deep catch stroke, for which the arm is extended and which pulls the water like a boat paddle. In the other, we have proponents of the propeller stroke, also known as the sculling stroke, for which the arm is bent at the elbow and makes a slight S-shaped curve as it moves through the water. Now, thanks to researchers at Johns Hopkins University, we have our final answer: the deep catch stroke is more effective and more efficient than the sculling stroke. Finding that answer wasn’t easy. A Johns Hopkins news release reports that scientists from the department of engineering used high-precision laser scans and underwater videos of elite swimmers, then turned to animation software to change the shape of the static arm in such a way as to match the video sequence. The team then ran computer simulations to study the flow of fluid around the arm and the forces that acted upon the limb. Each simulation involved about 4 million degrees of freedom and required thousands of hours of computer processing time. Study author Rajat Miittal says his research disproves the long-held conviction of many swim coaches that the sculling stroke delivers more speed. “Sculling, in my view, is a swimming stroke that is based on an incomplete understanding of fluid mechanics,” Mittal said. “We found that lift is indeed a major component in thrust production for both strokes, and that certainly indicates that the arm does not behave simply like a paddle. However, the simulations also indicate that exaggerated sculling motions, which are designed to enhance and exploit lift, actually reduce both the lift and drag contributions to thrust. So, lift is in fact important, but not in the way envisioned by these early coaches who were trying to bring fluid mechanics into swimming.” Got that? Read more from Johns Hopkins.