On January 29th, 2017 we learned about

Freestyle swimmers can move faster by spreading out their fingers

My family recently attended a collegiate swim meet, which was punctuated by an astounding 1000 meter freestyle event. One swimmer began to pull ahead, first by one lap, then by two, and eventually swimming a full four pool-lengths ahead of her competitors and teammates. It turns out that we had stumbled upon none other than Olympic gold medalist Katie Ledecky, who actually holds the current record for women’s 1000 meter freestyle. This explained a lot, but there was still something very strange about seeing Ledecky swim so quickly— even as she pulled ahead, she didn’t really seem to be moving any faster than anyone else in the pool.

To be clear, Ledecky was obviously moving through the water faster than the other swimmers, but she seemed to be moving her arms through the water at a similar rhythm and pace as anyone else. Rather than more strokes per second, she was getting more power per stroke, probably in part to small adjustments that could greatly increase her efficiency as a swimmer. Researchers have found that even something as seemingly small as finger position in the water might be enough to net a swimmer a 12-second improvement over a race 1000 meters long.

Testing drag made by your digits

My second grader, I think like most of us, assumed that the best use of one’s hands in a freestyle stroke is to keep the fingers together to imitate a fish or pinniped’s flippers. Scientists working in simulations and with models in wind tunnels weren’t so sure, and tested the amount of turbulence and resistance fingers make in a fluid when spread at 0, 5, 10, 15 and 20 degrees apart. They found that at 10 degrees apart, spread digits created an optimal amount of turbulence that benefited the swimmer more than the small amount of water that passed between the fingers. Essentially, the turbulence from the spread fingers created a sort of virtual flipper around the hand, and that increased surface area then helped reduce the amount of drag from the rest of the arm moving through the water.

These results are going to be tested further on a swimming robot that can better imitate a full stroke of a swimmer, rather than just water moving over a hand at a constant speed. If swimmers like Ledecky start adding this to their arsenal of techniques, we might expect to see world records get that much shorter.

Source: How Top Swimmers Can Go Faster: It's All in the Fingers by Charles Q. Choi, Live Science

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