The fish kick may be the fastest swimming stroke yet:
Until recently, competitive swimming has focused almost entirely on what happens at the surface of the water. In early 19th-century England—which many consider to be the birthplace of the modern sport—swimmers raced using the breaststroke. A few decades later, Europeans learned a faster stroke when two Native Americans visiting London demonstrated a way of swimming they had learned growing up: the front crawl. One observer wrote, “they lash the water violently with their arms, like the sails of a windmill, and beat downwards with their feet, blowing with force, and forming grotesque antics.” The Brits eventually got over their shock. The backstroke came next, followed in the early 20th century by the butterfly stroke, which overcame the drag of the underwater recovery required by the breaststroke. The butterfly became the second fastest stroke after the front crawl.
All swimming at the surface shares the same speed restriction. “You’re always limited by your hull speed,” says Ryan Atkison, a sport biomechanist at the Canadian Sport Institute Ontario. It’s a nautical principle that also applies to swimmers. The theory goes that a swimmer on the surface cannot go faster than the bow wave that he or she creates. The bow wave increases with swim speed until, in theory, it stretches along the whole length of the swimmer’s body. Atkison says that the maximum speed is one body-length per second, which is about 1.9 to 2.6 meters per second for a swimmer about 2 meters (6 feet, 5 inches) tall.
“You can’t go any faster than that unless you climb up over top of that wave,” says Atkison. “Some animals can, like dolphins can porpoise and jump over top of that bow wave, but humans can’t physically climb out of that trough,” he says. “The only real way to get faster is to be better under water, where we don’t really have those upper limits on speed.”
Coaches began to take advantage of this fact in the 1980s, when Harvard University coach Joe Bernal realized that some of his swimmers were faster if they stayed underwater and dolphin kicked. This is essentially identical to the fish kick, except that the swimmer is flat on his stomach, rather than turned on his side. Some especially strong underwater swimmers stayed submerged almost the entire length of the pool, since there was no rule against it. That all changed in 1998, when FINA, the world governing body of competitive swimming, ruled that swimmers performing the backstroke had to surface after 15 meters.
Hyman came of age as a world-class swimmer during the underwater revolution. “I was 13 when I started staying under water longer than is typical,” she says, explaining she could go 30 meters without breathing. “I found I could be faster under water than at the surface.” Most swimmers were using the dolphin kick to propel themselves underwater, but Hyman’s coach, Bob Gillet, wanted to experiment. In 1995 he came across a study in Scientific American about how tuna were able to swim at almost 50 mph, where dolphins top out around 25 mph. The study found that the flick of a fish tail generated more efficient thrust than that of a marine mammal tail. Gillet wondered whether the dolphin kick might be more powerful on its side, so the undulations were horizontal, like those of a fish.
One cool December day in Phoenix in 1995, Gillet put it to the test. Hyman showed up for practice at Gillet’s outdoor pool, and he asked her to try it. “In the most respectful way, I called him a mad scientist,” she says. Her first attempts were awkward, and she ended up three lanes over from where she started. But she got better, and soon she was cutting through the water like an eel. She was going faster than she did with the dolphin kick. Faster than she had ever swum before. This gave Gillet another idea.
They went to the local country club pool, where the lighting was brighter and Gillet could walk out to the edge of a diving board to capture video. They took a long, thin rubber tube, fastened it to Hyman’s wrist, ran it down the length of one side of her body, and fastened the other end to her ankle. Then they filled the tube with store-bought food dye, and Hyman corked the tube with her thumb. She jumped into the pool, released her thumb, and took off as Gillet filmed. What they saw in the footage afterward astonished them. The dye swirled out to reveal huge vortices after each of her horizontal kicks. Gillet suspected that these miniature whirlpools, reaching 4 feet in diameter, propelled her forward. He also thought it was possible that when Hyman did the dolphin kick facedown, the bottom of the pool and the surface of the water interfered with these vortices and slowed her down.