This Week in Research: The Right Way to Swim; Stop Washing Your Children

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Sometimes science explores things that are so high-level we amateurs have a hard time fitting them into our brains. But sometimes they use their science-power to answer a question we’ve all been idly wondering for a long time:  in this case, what’s the fastest way to get from one side of the pool to the other? (No, the answer is not “get Michael Phelps to give you a piggy back ride.”)

As anyone who’s spent time splashing around in the deep end can tell you, there are two basic arm movements that can propel you through the water. One, the deep catch stroke, is akin to a boat paddle; the other, sculling, involves the swimmers’ bent arms whirring to the side, almost like a propeller. Both strokes are used in training by Olympic caliber athletes, and both have their advocates. The deep catch was the dominant technique until Doc Counsilman, coach of the U.S. men’s Olympic team and advocate of sculling, led his team to a combined 21 golds in the 1964 and 1976 games. But questions still remained as to which stroke was superior — until now when, thanks to fluid mechanics experts at Johns Hopkins, we finally know which swimming stroke is definitively better. “This is a result that is simple but sweet, which is something we usually struggle to arrive at in research,” according to Rajat Mittal, a professor of mechanical engineering at Hopkins.

And the winner is (drumroll please)…

The deep catch stroke! To figure this out, Mittal (who got his start studying how fish swim on behalf of the U.S. Navy) used high-precision laser scans to capture images of elite swimmers doing their thing. After plugging that data into animation software, the research team ran simulations to study how fluid flowed around the swimmers’ arms. The deep catch stroke won out.

“Sculling, in my view, is a swimming stroke that is based on an incomplete understanding of fluid mechanics,” Mittal says. “We found that Doc Counsilman was not correct overall about the sculling, but in some ways he was more correct than he would have ever thought. We did find 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.” Words to remember as you head to the pool this weekend.


Children are dirty. Germs are bad. Soap and toothpaste are good. Except that, according to new research from the Johns Hopkins Children Center, too much antibacterial exposure might make children more prone to allergies.

The research team, lead by Dr. Jessica Savage, looked at a national survey of 860 children ages 6 to 18. When they measured both levels of antibacterials (which they did by looking for traces of the preservatives used in hygiene products) and levels of IgE antibodies (immune chemicals linked to allergies), they found a clear connection.  “We saw a link between level of exposure, measured by the amount of antimicrobial agents in the urine, and allergy risk, indicated by circulating antibodies to specific allergens,” Savage said.

Which isn’t to say that Purell is giving your kids a pollen allergy; according to researchers, it’s more likely that antibacterials work too well. The over-soaped, over-sanitized child doesn’t get early childhood exposure to common pathogens — which, counterintuitively enough, might actually be necessary to build a healthy immune system. So go ahead, let the kid play around in dirt for a little while. It’s healthy!

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  1. Goodie, another bit of actual research that shows we are over-doing it in protecting our kids. It has been self-evident to anyone who has been observing family behaviour the last couple of decades: scheduled play-time, layers of safety gear, and little to no allowance for the occasional skinned knee or bruised arm. I hope the good doctor’s work gets more attention than some previous work has gotten.
    Let the kids play!

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