Dustin, left, Danielle and Devin Wahl plan to become the first sibling trio to swim across the British channel on July 22. Success will mean overcoming cold water and strong currents. (Courtesy of Devin Wahl)

For Devin, Danielle and Dustin Wahl, the numbers aren’t promising.

A person’s chance of swimming across the English Channel is roughly 50-50, and that’s if you have the discipline and tolerance for pain of yoga masters and pillar saints. The chance of three people accomplishing the task simultaneously is considerably smaller, 12.5 percent. One in eight.

The Wahl siblings are hoping to beat those odds on July 22.

Of course, they have other things going for them, such as genes and training.

Age 19 to 24 and the children of endurance athletes, they have shown they have more than just potential. Danielle has swum the Channel once already. Devin has finished two Ironman-distance triathlons: 11 hours of nonstop exertion. Dustin, the youngest, is training five hours a day. They are each swimming 28 miles a week, lifting weights and taking ice baths to condition themselves to frigid water.

Devin Wahl trains for the swim of a lifetime at Gunpowder Falls State Park in Chase, Md. Wahl is planning to swim the English Channel this month along with a brother and a sister. (Linda Davidson/The Washington Post)

Although sibling pairs, and even twins, have swum the Channel together, three siblings never have. The feat is one of the few “firsts” still unclaimed since Matthew Webb, a captain in Britain’s merchant marine, became the first documented Channel crosser in 1875. Since then, about 1,400 people have done it.

The Wahls are also raising money for research on Alzheimer’s disease, which killed one of their grandfathers and afflicts an uncle.

“We want to raise consciousness in the younger generation, first and foremost,” Devin said. “Sometimes you have to do something incredible, and near impossible, to do that.”

“Incredible” is one word for swimming the English Channel. “Hellish” might be another.

The Channel is one of the busiest shipping routes in the world, with 500 ships a day passing through its narrowest part, Dover Strait, where swimmers cross. The tides range from 17 to 22 feet in height, depending on the phase of the moon. As a consequence, the currents are strong and most swimmers are forced to take an S-shaped route whose distance is far longer than the 21 miles separating England and France at the narrowest point. Those currents often carry rafts of stinging jellyfish that swimmers must endure.

Most of all, the Channel is cold.

During the June-to-September swimming season, the water temperature ranges from 55 to 65 degrees. The two organizations that certify swims — the Channel Swimming Association (CSA), founded in 1927, and a newer rival, the Channel Swimming & Piloting Federation (CS&PF) — don’t allow wet suits or any insulating garments other than bathing suit and cap. Nor do they allow swimmers to touch a boat or another person during the swim (although they can be handed food and drink).

Baltimore artist Katie Pumphrey began training to swim the English Channel. She shares what she thinks it will take to swim the dangerous crossing. (Whitney Leaming/The Washington Post)

Spending hours in water as cold as the English Channel’s taxes the body in ways most people will never experience and couldn’t survive. Channel swimmers survive because they habituate themselves in advance.

The average crossing takes about 13 hours. The fastest time last year was either 9 hours 2 minutes by an Englishwoman, according to CSA, or 9 hours 14 minutes by a New Zealand man, according to CS&PF. (The record books of the two organizations differ slightly.) Danielle Wahl, now 21, was the fastest American of either sex, finishing in 9 hours 50 minutes.

Such is the ability of human beings to train and persevere that more than two dozen people have swum across the Channel and back without stopping. Three people — two men and a woman — have done three-way crossings, which required 28 to 38 hours of continuous swimming in water 35 degrees below body temperature. It may be a feat without equal in the annals of human endurance.

‘We want to be the first’

The Wahl siblings grew up in Colorado Springs. Their father is a dentist and their mother a substitute teacher. There are five children in all.

Their parents have done marathons, open-water swims and triathlons, and the children began endurance sports at young ages. Devin, Danielle and Dustin first got the idea of swimming the English Channel together several years ago but decided to put off an attempt until Dustin, now 19, was older.

About a year ago, however, Devin — at 24, he is the oldest of the siblings — was noodling on the Web when he came across the mention of three siblings in Australia who were planning a simultaneous crossing this August. That clinched the idea.

“It kind of brought out our competitive edge. We don’t want to be the second three-sibling team that’s done it. We want to be the first,” he said.

The most propitious times for crossing — mid- to late August — were already booked, so the siblings had to settle for a late-July slot. To qualify with the Channel Swimming Association, they each had do a certified six-hour swim in water no warmer than 60 degrees. They had to pay about $680 each to register. The fee pays for, among other things, an official observer from the organization. They also each engaged a boat and pilot (whose judgment on when to start can be key to a swimmer’s success) for about $3,260 apiece.

All that was left was the training.

Danielle and Dustin are both students at Centre College, in Danville, Ky. Danielle, majoring in psychology, will be a senior in the fall; Dustin, studying civil engineering, will be a sophomore. Devin graduated from Colorado College, in his home town, in 2012 after majoring in neuroscience. He works in a National Institute on Aging lab in Baltimore, where he lives. He hopes to go to graduate school in neuroscience sometime in the next few years.

Danielle and Dustin are spending the summer in Colorado Springs, intensifying their training now that the school year is over.

“I needed to keep academics the No. 1 priority — academics, finals and homework,” Dustin said. “This summer, I told myself that I had to treat training like a job. If people work eight hours a day, I had to train five hours a day.” Once a week he swims for two hours in a meltwater lake whose temperature is in the mid-60s.

As part of her preparation, Danielle last month swam the Catalina Channel, from Catalina Island to Los Angeles: 22 miles in water 64 to 68 degrees. She began at midnight after a nauseating 21 / 2-hour boat ride from the mainland. The swim took 8 hours 19 minutes.

“I thought it would be a good training swim for the English Channel,” she said. “Just another big open-water swim that few people attempt.”

Devin, who works 10-hour days in the lab, trains five days a week at Meadowbrook Aquatic and Fitness Center in Baltimore, the natatorial home of Olympian Michael Phelps. Each weekend he does a long swim in the Chesapeake Bay at Gunpowder Falls State Park east of Baltimore. On a recent Sunday, he put in three hours before declaring the water too warm and heading back to the pool to do two more.

Watching from the beach that day were Daniel Camiletti-Moiron and Marta Gonzalez-Freire, both 31 and Ironman triathletes, who work with him in the NIA lab. They were offering solidarity, although Devin was little more than a black dot going back and forth offshore.

Endurance sports are for people comfortable with their own company. There’s no team play and very little socializing. In marathons, the terrain and scenery change, and in triathlons you switch from swimming to cycling to running. In open-water swimming, nothing changes, except when things get worse. The water is dark. The only view is a rhythmic glimpse of the horizon. The body’s motion is repetitive. Practically speaking, the end is never in sight.

It’s the solitary confinement of sport.

Against the evolutionary tide

Human beings are tropical creatures. Swimming the English Channel requires that the body blunt or ignore evolutionary adaptations that would normally make such an activity impossible.

When a person jumps into cold water, a “cold-shock” response causes intense discomfort, a racing heartbeat, and fast, shallow breaths. As the skin cools and resets its sensitivity, the person feels better. However, as the body cools further, blood is shunted away from the limbs, which are colder than the trunk, in order to maintain core temperature. With further cooling, the body begins to shiver, which is nothing more than involuntary movement that generates heat.

Six decades of research has shown that repeated cold-water immersions lasting only a few minutes can eliminate cold-shock. Longer immersions (about 45 minutes) can suppress shivering and allow the body to tolerate a reduced core temperature.

The final result of training is a physiological compromise that permits a Channel swim. The body gets cold, but not so cold that it can’t do the work of swimming, and that work in turn produces enough heat to keep the body from getting colder.

A variable that helps negotiate the compromise is body fat.

Fat insulates against the cold. In fact, each millimeter of fat under the skin is equivalent to an increase in the temperature of the water of 2.7 degrees. That’s why Devin and Dustin are madly trying to gain weight as part of their training.

“Few things are absolutely true when it comes to Channel swimming except this,” said Michael J. Tipton, a physiologist at the University of Portsmouth, in England, who has spent a career studying human adaptation to cold. “You will find fat, fast swimmers and thin, fast swimmers. You may find some fat, slow swimmers. What you’ll never find is a thin, slow swimmer. They’ll be dragged out time after time with hypothermia.”

Mind over matter

Which brings us to the brain. Almost everyone agrees it’s the most important organ for getting one across the Channel.

The brain can play tricks. In her crossing last year, Danielle thought she saw two dolphins. But there were no dolphins. The water at the start was 55 degrees. At one point she stopped and said she was too cold.

“But then I kept going.”

Devin had similar doubts in Ironman triathlons.

“It essentially comes down to mind over matter. You do have to put your mind in a different space.”

Each of the siblings will have a boat, and none will be told how the others are doing. Only at the end will each know whether the others finished, or are likely to.

In a 2006 essay on the history of endurance events, the South African exercise physiologist and ultramarathoner Timothy D. Noakes concluded that “when the activity is prolonged, the mind not the body becomes the ultimate determinant of what can be achieved. . . . It is the mind that determines who chooses to start and who best stays the distance.”

The Wahl siblings will know more about that in a week.