The fish kick, if done properly, is the fastest way for a human to swim. The technique requires a swimmer to lie sideways and wiggle her body in a fluid motion that mimics that of a minnow or an eel. At the 2000 Olympics, American swimmer Misty Hyman fish-kicked her way to gold in the 200-meter butterfly, beating out two heavily favored Australian swimmers.
In the video below, you can watch Hyman employ the fish kick at each turn. Susie O’Neill—an Aussie whose dominance earned her the nickname “Madame Butterfly”—stays with Hyman through the first 100. But when they reach the final turn, Hyman fish kicks back into a clear lead. O’Neill can’t recover.
The fish kick is the Devils Hole pupfish of the pool, a rarely seen and fascinating specimen. It emerged in Sunday night’s 4-by-100 men’s freestyle relay, when the United States’ Ryan Held used the kick on his turn in the third leg of the race. But Held’s fish kick was an unusual sight in Rio. If it’s the fastest kick in the world, why don’t more swimmers do it?
For one thing, if a swimmer screws up the fish kick, he’s risking disqualification. Per the rules outlined by Fédération Internationale de Natation, the sport’s international governing body, swimmers attempting the fish kick after turns in downward events—the breaststroke, the butterfly, and the freestyle portion of the individual medley—must not rotate onto their backs, even by a few degrees. In the backstroke, the opposite mandate applies: Athletes who rotate toward their stomachs will be DQ’ed.
A second problem: The fish kick is supremely difficult to master. In addition to keeping their bodies rotated just so, swimmers must worry about veering away from the center of their lanes, since it’s pretty much impossible to keep your eye on the lane markings when you’re on your side.
Here’s Hyman doing it in a 1996 100-meter butterfly race. Compared with her competitors, she’s underwater for much longer, but still maintains her central lane position:
Why did Misty Hyman use the fish kick? Because she knew she had to take risks to win. After reading an article in Scientific American on the swimming techniques of literal fish, Hyman and her coach Bob Gillett developed her signature kick. In an interview with the Chicago Tribune a few years before her Olympics upset, Hyman said, “I’m not 6-feet tall. … For swimmers like me, it’s either use steroids or use your brains.”
The fish kick isn’t the only technique that gives swimmers an edge. In the 1988 Seoul Games, American swimmer David Berkoff helped the U.S. win gold in the men’s 4-by-100 medley relay by swimming almost the first 50 meters of his backstroke leg underwater, propelling himself with a dolphin kick. To execute that move, a swimmer stretches flat out—facing either up or down—and kicks his legs together in a fluid motion that resembles that of a dolphin’s rear fin. The underwater dolphin kick was too much of a performance enhancer for swimming’s powers that be. In 1988, FINA declared that backstrokers had to surface within 15 meters of starting or turning. In 1998, two years before Hyman’s Olympic victory, the governing body passed the same rule for butterfly. Later, it banned the underwater dolphin kick for freestylers as well.
The fish kick, though, is even better than the dolphin kick. A piece published in Nautilus in 2015 explains the physics. Like the dolphin kick, the fish kick takes place underwater, where drag is less of an issue. But the sideways fish kick has an advantage over its dolphin cousin, because the turbulence it creates on each side of the body reverberates sideways into the pool uninterrupted, rather than being stopped by the pool’s bottom or the water’s surface.
When Hyman practiced the fish kick, she often surfaced 30 meters from the wall, which was illegal under the 15-meter rule. She managed to shorten it for her Olympic swim, but it took a lot of practice. Training to perfect the fish kick may be too much of a time investment for athletes that are already poised to win via their brute strength. Hyman, who now coaches swimming at Arizona State University, says only a few of her athletes have used the fish kick with any success.