PORTLAND, OREGON—In elite swimming competitions, hundredths of seconds make all the difference. And by simply spreading your fingers, you can shave some of that time off, according to a study presented here last week at the 69th Annual Meeting of the American Physical Society Division of Fluid Dynamics. Physicists used 3D-printed plastic hand and arm models to consider the impact of five different finger positions on swim speed: pointer, index, ring, and pinkie fingers spread by 0°, 5°, 10°, 15°, or 20°. (In all cases, the position of the thumb was held constant.) The researchers measured drag over their model in a wind tunnel rather than a pool to avoid the influence of surface waves. They found that the model with its fingers spread 10° created the most drag because the slight opening between the fingers still obstructed air flow. Because more drag gives a swimmer more to push against and propel him or herself forward, the team concluded that freestyle swimmers were the most efficient when they spread their fingers slightly. Making assumptions about hand size and stroke rate, the researchers calculated that a finger spread of 10° could boost a swimmer’s speed by 2.5% compared with swimming with fingers held together. That speed difference translates into several tenths of a second over a 50-meter freestyle race, an enormous margin considering that the 2016 Summer Olympics 50-meter women’s freestyle race was won by 0.02 seconds.