Rajat Mittal, a professor of mechanical and aerospace engineering at the George Washington University, was studying dolphins for the U.S. Navy five years ago. “We were asked to understand how fish swim so efficiently,” Mittal says, “and it seemed like a natural extension to apply this to human swimming.”
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They decided to “essentially compare these swimmers to the dolphin, assuming that the dolphin is the ultimate swimmer,” Mittal says. “And the thing that we found is that Michael [Phelps] is able to use his body in a way that is very, very different from the other athletes, and also seems to be much closer to dolphins than we have seen for any other swimmer.”

The dolphin kick first hit Olympic swimming big-time 20 years ago, after Harvard backstroker David Berkoff figured out something fundamental. “It seemed pretty obvious to me that kicking underwater seemed to be a lot faster than swimming on the surface,” Berkoff says.

That’s because there’s turbulence and air on the surface of the water, and they create resistance. The “Berkoff Blastoff,” as it was called, was used at the start and after turns, with long stretches of that underwater undulating kick.