SPORTS: Researchers Point to Fingers as Key to Speed in the Water

by Karin Zeitvogel

Watch a video of Michael Phelps swimming, and you'll notice that his fingers are slightly spread as he slices through the water.

Phelps swims with forked hands, and a U.S. researcher is urging all swimmers to do the same if they want to go faster.

Swimming with fingers apart can result in a whopping 53 percent increase in total force, says Duke University engineering professor Adrian Bejan in a study published in June in the Journal of Theoretical Biology.

If the distance between the fingers is just right – roughly half the diameter of each finger – it creates an invisible web between digits, which gives the swimmer a boost in force and faster speed in the water, Bejan said.

“The finger moves through the water and a sheath of water essentially moves with it, creating a finger that looks thicker than it really is. Think of it like honey stuck to a spoon,” he told Water Citizen in a phone interview.

Greater force is the key to going faster in the water, and producing greater force is the job of the hands, Bejan said.

“A faster swimmer is one who looks like a bigger wave above the water, and you get bigger above the water by having the force to lift yourself above the water, which you do by having greater downward force,” from your hands, he said.

In essence, the bigger the hands, the greater the force. And, “If you want a palm that is bigger, you want bigger fingers,” Bejan said. Spreading them slightly in the water achieves that.

Phelps spreads his fingers instinctively but many coaches these days tell their swimmers to do so. If a lot of people in the lap lanes at the local pool are contemplating their hands, you know why.

The swimmers’ fingers principle is based on the constructal law, devised by Bejan in 1996. Constructal law holds that “anything that moves, from rivers to trucks on highways to swimmers and runners, does so with morphing configurations that allow movement to be easier and easier,” Bejan said.

The results of the fingers study show that a slight adjustment in body configuration can bring a “significant change in force,” Bejan said, wondering if the next swimming aid will be tiny wedges that sit between swimmers’ fingers to hold them just the right distance apart.

Finger spread is just one of Phelps’s secrets, of course. His hands are said to be the size of dinner plates even without the invisible inter-finger webbing.  He also has other attributes that make him the record-breaking swimmer that he is:  he’s tall, – 6 ft. 4 in. (1.93 meters) -- has size 14 (Eur 47) feet, a 6 ft. 7 in. (2 meters) arm span, a long torso and comparatively short legs.

In 2008, Bejan used the constructal law to predict the triumphs of “bigger, taller athletes” like Phelps at the Beijing Olympics. Two years later, Bejan, who’s originally from Romania, teamed up with Edward Jones, an African American professor at Howard University in Washington, to use the constructal law to explain why whites dominate in the pool and blacks of West African origin, like Jamaica’s Usain Bolt, in sprint-distance track events.

In that study, Bejan found that "the swimmer who makes the bigger wave is the faster swimmer, and a longer torso makes a bigger wave. Europeans have a three-percent longer torso than West Africans, which gives them a 1.5-percent speed advantage in the pool."

Individuals of West African origin, meanwhile, have longer legs than people of European origin. That puts their  center of gravity – roughly speaking, the belly button – around three centimeters (1.18 inches) higher than whites', said Bejan.

“Locomotion is essentially a continual process of falling forward, and mass that falls from a higher altitude falls faster,” he said.