In the 1960s, Indiana University men’s swimming coach, James “Doc” Counsilman, decided that lift, rather than drag, could and should provide a majority of the propulsion for human swimmers, and that the way to generate lift was to scull, or move the stroking arm through an S-curve underwater, rather than paddle in a “deep catch” style. Now the Johns Hopkins scientists who previously studied the breaststroke have moved on to studying the crawl:
They began by creating a virtual animated arm, using laser scans and motion-capture videos from Olympic-caliber swimmers. “We decided to separate the arm from the rest of the body so the we could study, in isolation, the underwater flow dynamics” around a swimmer’s arm during the freestyle stroke or backstroke, says Rajat Mittal, a professor of mechanical engineering at Johns Hopkins and a devoted recreational swimmer, who oversaw the study.
They then gathered underwater videos of elite swimmers, supplied by USA Swimming, which they categorized as displaying either a sculling or a deep-catch stroke.
The scientists ran their animated arm through multiple simulations of each stroke, requiring thousands of hours of computer time.
The result was “a bit of a surprise,” Dr. Mittal says. It turned out that lift was, as Doc Counsilman had maintained, important for efficient, and therefore fast, stroking. In all of the scientists’ simulations, lift provided a majority of the propulsive force.
But sculling did not supply much lift. In fact, it impeded both lift and drag. “Our shoulders won’t twist all the way around,” Dr. Mittal says, meaning our arms won’t lever about as ship propellers do, and the amount of lift we can create by sculling is small.
The better choice for human propulsion, he says, was the paddlelike deep-catch stroke, which actually produced more lift than sculling, along with a hefty dose of drag.
An effective deep-catch stroke requires considerable shoulder strength, which many swimmers lack, making a sculling-based stroke easier for them, at least until they develop robustly muscled shoulders.
“How you roll your body in the water with each stroke will also matter,” he says, as will overall fitness. “Sculling is less fatiguing,” so less-fit swimmers may opt to scull, he says.
But for fit, powerful swimmers, or those who aspire to become such, “my advice would be to use the deep-catch stroke,” he says.