Why Elite Swimmers Mimic Fish and Dolphins

When you watch swimming events during the Rio de Janeiro Summer Olympics this week, make a note of the weird way the humans in the pool are moving. To be clear: It’s suspiciously unhumanlike, more like a slithering eel or a diving porpoise than what you’d see on a day at the beach.

There’s a reason why Olympic swimmers sometimes look more like they belong in your local aquarium than at a pool: Dolphins, fish, and lampreys are the ideal form to copy if you want to compete at a world-class level.

In the 1980s, Harvard University coach Joe Bernal realized that if a swimmer stayed underwater, remained flat on their stomach, and kicked in a movement similar to a dolphin, they were much faster. According to Nautilus, swimming coach Bob Gillet tried a different method 15 years later after reading a study claiming tuna could swim almost 25 mph faster than dolphins — so he had his swimmers swim on their side and horizontally move across the pool. Lo and behold, his swimmers were faster than ever with the (tuna)fish kick.

Why these methods work so well is because they force swimmers to use undulatory motions — a type of motion that’s wave-like, allowing an animal to propel forward. Underwater undulatory swimming is considered one of the fastest ways a human can possibly swim because the combination of moving wave-like while staying beneath the surface keeps swimmers away from wave drag. Contrary to what you might assume, in other words, it’s not the power of your arm strokes or how frequently you kick that’s key — it’s how you utilize your body to maximize underwater propulsion.

A 2014 study published in the journal Human Movement Science examined how close a human swimmer could approach the ideal undulatory wave. They found that those who did not avoid wave drag could end up moving 20 to 50 percent slower, depending on the swimming style and ability of the athlete. Athletes that could stay below the surface — moving their hands, shoulders, and toes in an asymmetrical way while keeping their form in a linear body wave — were much faster.

One year later, Harvard researchers concluded that the flow of water creates a more efficient swim. They focused on jellyfish and lampreys, finding that the two types of aquatic creatures suck water toward them to move forward, rather than pushing water behind them. This goes back to the idea of undulation and its ability to create pockets of low pressure that minimize drag.

Olympic athletes are well versed of these advantages and try to incorporate as much fishy behavior as legally possible in their swims. While it’s illegal to dolphin kick the whole way through, swimmers can do the underwater movement at the start of the race — in a 100-meter race, for example, a swimmer can still make 30 percent of their total distance with just their dolphin kick. Michael Phelps, for example, unleashed a massive dolphin kick on Sunday’s 4x100 meter freestyle relay race, helping his team clinch the gold.

Fellow American Ryan Lochte, whose dolphin kick is one of his strongest suits, is also expected to do some serious damage with his own, new freestyle method that utilizes undulatory techniques. While his competitors are taking the turn with a flip, Lochte is staying on his back, diving deeper, and staying underwater longer. This allows him to avoid the turbulence at the surface, minimizing drag and allowing him to pop up ahead of his competition.

And then there is the elusive and incredibly difficult fish kick. It hasn’t shown up much in Rio — newly-minted gold medalist Ryan Held is the only one to use it so far — but it got Misty Hyman the gold at the 2000 Games. It’s assumed to be the fastest way a human can swim, because of the aforementioned use of physics. But it’s also just straight-up hard, because of a simple fact: While we can mimic fish, the best we can manage is a lukewarm impression. When it goes wrong, you move sideways across the pool; when you nail it, you win gold and the right to utter JEAH.