“Pass the rock,” says Kyle Korver.

The six-foot-seven Atlanta Hawks guard is arguably the best shooter in the NBA, so this should be funny, given the circumstances. See, we’re not on a basketball court. We’re not even on land. On a sunny California afternoon in June, in a pristine harbor along the coast of Santa Cruz Island, 30 miles south of Santa Barbara by boat, we’ve been taking turns lumbering along the shallow seafloor for the past three hours lugging an 85.2-pound stone that Korver procured from a nearby beach. It feels a little lighter in the ocean, thanks to the relative density of water, but it’s still a heavy-ass rock.

Korver is treading water above me. I drop the boulder below his feet and surface. Struggling for air, I try to ignore the spasms in my hamstrings and the giggling of girls on a nearby boat. It looks nice over there, with the beer and the snacks and the lounging.

Smiling sincerely, with huge white teeth—a 33-year-old, brown-haired, Midwestern, XXL Cousteau—Korver freedives a few feet into the churning murk to retrieve and then run underwater with our rock. Through my goggles, I can just barely see him leaning forward like a running back, pushing off the soft, downward-sloping sand with his size 14 neoprene booties. It’s a slow-motion sprint-with-stone that would look silly on land. But he’s Walter Payton in a wetsuit down here, seven feet below.

“This is about testing your abilities in a foreign environment,” says Marcus Elliott. “It's not a ride at Disneyland or a Tough Mudder. And it's really hard. You have a 50 percent chance of success, at best.”

Our suits protect us from the chilly water, but they won’t deter the great whites, which are common here, trolling for wayward flesh. Korver dreamed about these sharks recently; they’ve been in the news. The thought of an exploratory bite isn’t entirely unwelcome to me, however. It would result in a return to the boat: No more treading water wearing 15-pound weight belts. No more stinging eyes, stuttered excuses, and chafed-raw fingers.

Alas, the sharks aren’t hungry. Thirty or forty seconds after passing the rock to Korver, it will be my turn to take the rust-colored sedimentary stone—somewhere between five million and thirty million years old, probably never molested by humans until today—for yet another march along the 200-meter stretch of the Coches Prietos anchorage that, for our purposes, constitutes a lap in this Sisyphean relay.

Fourteen laps down, ten to go.

We’re toiling alongside three of Korver’s pals here in Santa Barbara, where he and his family live in the off-season. There’s Marcus Elliott, 48, the mastermind behind this sufferfest, a Harvard-trained sports scientist who works with pro athletes and enjoys all-night jogs; Deyl Kearin, 34, a mellow real estate investor who ran 150 miles across the Sahara in 2012 and looks like he could be Laird Hamilton’s clean-cut younger bro; and Nelson Parrish, 35, a sturdy, Alaska-bred, former junior Olympic skier whose artwork, collected by John Legend and Rob Lowe, depicts “the color of speed.”

I reconsider what Parrish said earlier: “Just run underwater for the time it takes to make your morning coffee—get your mug, pour a cup, add milk and sugar, stir…”

“We’re all a bit nuts,” he told me soon after we met, stating the obvious. Elliott underwent emergency intestinal surgery just three weeks ago, and he still didn’t bail on what he calls, with characteristic understatement, “today’s run.”

“The doctor said no baths,” Elliott told me. “But he didn’t say anything about the ocean.”

This is the second time in two years that these four guys have gathered to push themselves to their limits in what has become an annual rite of enlightened punishment. This year, Elliott thought schlepping rocks undersea would do the trick. So it is that we’ve been shuttling two stones—the other would weigh 68.5 pounds on Korver’s digital scale once we got it back home—in rotating teams of two and three. I’m the swingman, which means I don’t carry it quite as often. But I’m suffering all the same. Korver pushed to make the relay a 5K. “It sounds better than two miles, right?” he said before we started. This guy set an all-time NBA record last season for consecutive games with a made three-pointer, and he believes he did so because of the ritual we’re experiencing right now. Ritual being a euphemism, of course, for something far, far worse.

“It’s called misogi,” Korver almost whispered when we first spoke about it last year on the phone.

“Can you spell that?” I asked.

He paused. “I’m not sure.”

The truth is, none of the guys is certain how to spell it or say it, or even exactly what it meant thousands of years ago in Japan, where the general concept originated. But each man speaks of it with religious conviction. Kearin, the ultrarunning realtor, has purchased Misogi.com—his preferred spelling—whose homepage announces: “Learn about a concept that will forever change the way you approach your life.” Elliott agrees. “I’ve been innovating sports science for 20 years,” he says, “and there are no substitutes for the tools gained in misogi.”

Elliott has been a team physiologist for the New England Patriots and a sports-science consultant for the Utah Jazz. In 2005, he founded Santa Barbara–based Peak Performance Project (P3) “to apply cutting-edge science for optimal athletic achievement.” He helps athletes at all levels, including Brooklyn Nets point guard Deron Williams, former San Francisco Giants pitcher Barry Zito, and a few U.S. Ski Team members. He recently signed a contract with the NBA to analyze the physical mechanics of each of its incoming players, the first league-wide effort of its kind.

If you visited P3, Elliott’s team would spend three hours figuring out your body. Using a 3-D motion-analysis lab, they’d watch you perform your sport. They’d collect 5,000 data points. In the end, they’d know that you have, say, six degrees less mobility in your left ankle than your right, which is causing your chronic back problems.

But Elliott isn’t just another data-obsessed fitness nerd. He’s more of a philosopher-adventurer than a technician. And he wants to spur an awakening. “We live in a lapdog culture,” he often says. “But that’s not our genetic need. Our capacity is far greater than we realize.” Bear with him.

In 1993, before his second year at Harvard Medical School, Elliott backpacked Wyoming’s Wind River Range with his best friend, an elite judo competitor and Rhodes scholar finalist. “Our relationship was based largely on a common drive to kick each others’ asses,” Elliott says. They flew from Boston to Wyoming, slept in a field by the airport, and hitched to the trailhead. While trudging 12 hours a day, his buddy told him about a “judo concept,” Elliott recalls, “borrowed from an ancient Japanese religious ritual.”

The idea, as the friend interpreted it: take on challenges that radically expand your sense of what’s possible.

For 15 years, Elliott thought about what his friend called misogi. “We’ve evolved with a desire to challenge ourselves,” he says. “It was necessary to get the tribe over the pass in winter, to hunt the mammoth. Now we live in the center of the table. We’re afraid to fail. Fuck that! How can you reach the edge of your potential without risking failure?”

Elliott gradually honed his own version of misogi, which would require completing only once or twice a year. “If it’s hard enough,” he believes, “the lesson will last.”

“This is about testing your abilities in a foreign environment,” he says. “The more blind, the more bold and adventurous the effort.” There’s no entry fee. No spectators. “It’s not a ride at Disneyland or a Tough Mudder,” he says. “It’s a personal quest designed by you. And it’s really fucking hard. You have a 50 percent chance of success, at best.” Regardless of the outcome—the thinking goes—you’ll realize your potential.

So what really is misogi? The first written reference occurs in the eighth century, in one of the earliest Japanese texts. In the myth, says Janine Sawada, a professor of religious and East Asian studies at Brown University, a god named Izanagi goes to the netherworld to find his wife, Izanami. This was a taboo journey. So Izanagi stops after he comes out and washes off, thereby purifying himself.

As the centuries passed, misogi came to describe more adventurous acts of purification. According to Sawada, “ascetic practitioners” wandered around the mountains of medieval Japan challenging themselves. “They’d go stand under waterfalls and chant esoteric Buddhist texts at the top of their lungs for a certain number of minutes or hours.” They did this in all seasons.

“Now,” says Sawada, “some Japanese who aren’t religious will douse themselves with cold water in nature as a self-cultivation practice. Westerners are getting involved, too, the way some go to Japan to practice Zen.”

A major Shinto shrine now has a branch near Granite Falls, Washington. “They get in the lake in their skivvies and do what they call misogi,” says Sawada. She wasn’t surprised to hear that some Americans—like Elliott, who believes that no one else is doing misogi his way—have adapted the ancient ritual in more athletic ways. “It’s got this cultural history behind it,” she says. “That’s appealing. But I think this modern misogi concept you’re describing is largely invented.”

In 2010, Kyle Korver set the record for the highest three-point field-goal percentage in an NBA season, hitting 53.6 percent from behind the arc. Some call him one of the best shooters ever. Genetics has something to do with this. His mother, Laine, once scored 74 points in a high school game. His six-foot-five father, Kevin, a pastor in Pella, Iowa, hooped, and his three younger brothers (Klayton, Kaleb, and Kirk) played in college.

Korver was an exceptional high school player—he also wrote a sports column called Kyle’s Komment—who went on to average almost 18 points per game during his senior year at Creighton University, in Omaha, Nebraska. But he was chosen late in the second round of the 2003 NBA draft by the Philadelphia 76ers and, as he himself acknowledges, was not expected to stand out much at the professional level.

After stints in Utah and Chicago, Korver was traded to the Hawks in 2012. “I’ve never been the fastest guy,” he says. “I’ve never been the tallest guy. But I know how to keep going, to grind. It’s probably not one of the sexier gifts you can get, but it works.”

Hawks general manager Danny Ferry agrees. “He works with a purpose and a focus and maximizes who he is,” Ferry has said. “He’s very diligent, very smart.”

These words are gratifying, as was Korver’s recent invitation to try out for Team USA. (He was one of the final cuts.) But at 33, only dedicated grinding will keep him at the top of the game. Korver has been working individually with Elliott, whom he knows from his days playing with the Jazz, during the past seven off-seasons.

It wasn’t until the summer of 2013 that Elliott introduced the idea of misogi. “He was perfect for many reasons,” says the sports scientist, “including that he has already developed internal drive—he has a search for truth, fearlessness, honor. He’s warrior-like and has an adventurous spirit. But especially because he’s always trying to be better.”

“I feel it,” Korver told Elliott after hearing about misogi. “But what are we doing?”

“Have you ever stand-up-paddleboarded before?” asked Elliott.

“No.”

“How do you feel about paddleboarding from the Channel Islands to Santa Barbara? Twenty-five miles across open water?”

“It sounds nuts,” said Korver, “but I’m in.”

So were Parrish and Kearin. They arrived at the Channel Islands not long after sunrise on an early September day in 2013. Kearin captained the support boat—someone had to. Parrish and Elliott paddled alongside Korver. They expected glassy water but instead found one-to-two-foot swells.

I don't know if it was an underwater version of Stockholm Syndrome. But something funny happens once you've been in the grip of a painful ordeal. The body and mind stop fighting it. Resisting takes too much energy.

Elliott had quickly explained the plan to Ferry, the Hawks’ GM, beforehand. “He was scared,” says Elliott, “but he didn’t stop us.” Korver’s hands, elbows, feet, and knees could get hurt. Even a twisted pinky could alter his painstakingly perfected shot.

Korver fell within 45 seconds.

“It was the side swell,” says Elliott. “We paddled on one side for the first four hours; the wind was trying to blow us to Malibu. We paddled on our knees.”

“After 20 minutes,” says Parrish, “my shoulder started locking up. For the first six hours, I didn’t think we’d make it.”

As the guys get wound up telling it, human blood began to chum the waters, along with an unwisely discarded chicken burrito. They mistook a giant sunfish for a shark.

“One fin. It looked like a buoy at first,” says Korver. “I was scared and hurting. My toes bled.”

“Kyle grew up in Iowa,” says Elliott. “He’s not a water guy. I felt responsible.”

“All I could do was focus on each stroke,” says Korver. “How far am I taking it out of the water? Where’s my release? My shoulders, my knees: Am I bent in? Can I balance better? I was analyzing every piece of that stroke and making it absolutely perfect.”

Nine hours later, they arrived on the mainland. Their first group misogi was complete. “It was an awesome moment,” says Korver. “At some point you have to accept that there is no backing out and you’re gonna set yourself on repeat until you cross the finish line. Excuses have to be dropped. Your mind has to focus. And you have to train that mindset. Everything falls into place by doing the smallest thing perfectly. That lesson from the misogi carried over to my shooting.” He made a three-pointer in his 127th straight game the next season—breaking Dana Barros’s all-time NBA record—and decided that he’d keep on doing misogis as long as his wife and Ferry would allow it.

When I ask Douglas Fields, a neuroscientist at the National Institutes of Health, what the benefits and drawbacks of our underwater rock running might be, he has a one-word answer: “Hypoxia.”

But, Fields continues, putting yourself through a difficult, foreign experience can have neurological benefits. “You can exploit the biochemistry of novelty,” he says. “The molecular processes that are engaged during a novel—stressful or traumatic—experience get turned on, and everything gets stamped into long-term memory.” Everything. This is why witnesses remember trivial details. “This effect can be used to advantage in training,” says Fields. Also, he notes, the prefrontal cortex controls the body’s stress, fear, and pain responses. Willing yourself to persist through pain and adversity can strengthen control of those responses. “That,” says Fields, “is what this Japanese method is doing: expanding your limits by strengthening forebrain control.”

Whatever the consequences, Korver hasn’t talked much with his Hawks teammates about misogi, because they might think he’s nuts. But one Hawks business consultant caught wind of it. Inspired by Korver, Jesse Itzler has lately been contemplating his own misogi. “I’ve run the USA Ultra Championships,” Itzler says. “But that’s planned, trained for. I’m struggling to nail something that fits the misogi mold. One thing I thought of, I call it By Sea, By Land, By Foot. It’d be a 100-mile paddle, a 100-mile run, and a 100-mile bike, back-to-back-to-back. But I don’t want to end up in the hospital.”

A week before I flew to California last June, Elliott revealed the task he’d chosen this year in an e-mail to the crew: “Although it’s used as big-wave hold-down training, I’ve never heard of anyone carrying rocks underwater for distance. Which makes distance irrelevant…and thus perfectly relevant as a misogi challenge.”

The night before our aquatic 5K, we meet at Korver’s house in the Edenic hills above Santa Barbara, looking out over the Pacific. We drink wine and eat gluten-free food as Korver’s two-year-old daughter, Kyra, and Kearin’s two girls crawl and run around us with toys.

“These kids need to start doing misogis,” says Korver.

“Walking could be a misogi,” says Parrish. “Balancing is tough at age two.”

Elliott’s intestinal injury actually resulted from a balancing problem. As Parrish puts it, Elliott was “dorking around on a carveboard with a video camera” during one of Parrish’s art projects, “and then suddenly he wasn’t cruising anymore.” Elliott isn’t the only one in recovery: Parrish is still rehabbing from a car accident that hurt his back and neck six months earlier, and Korver is dealing with a nagging foot ailment.

“I told my doc, ‘I’m gonna do a big water run in a few days,’ ” says Korver. “He thought that was a good idea.”

“He was imagining a shallow pool with old ladies,” says Kearin.

“Whatever. This misogi is doctor prescribed!” says Parrish.

The conversation then turns to the challenges of tomorrow. “We’ll start collecting data”—assessing the task and the temperature of the water with our bodies, not equipment—“and losing body heat at the same time,” says Kearin.

“After 15 minutes we’ll make some adjustments,” says Parrish. “Then life gets really simple. Pain comes in layers. You’ve just gotta go through all the layers. Then it’ll actually start to feel good.” He pauses, looking at me. “Whether you make it or you tap out doesn’t matter. Tomorrow you’ll have run a rock under the ocean farther than any of your buddies.”

“So the goal is two miles, right?” says Elliott, nursing a beer.

“I thought we were saying five kilometers,” says Korver.

“The last misogi was nine hours,” says Parrish.

“This is different,” says Korver. “We’re in the water.”

“Yeah. There’s no glide,” says Elliott. “Even if you’re getting a drink, you’re treading. You’ve got weight belts on. Holding your breath over and over. What if it takes us three hours to go one length and we’re sucking wind?”

Before disbanding, Kearin suggests a contingency plan: “If everything falls apart, there are two big peaks right above the anchorage. If we have to, we’ll rotate running rocks up them. So bring running shoes.”

“The misogis have turned into my grind activator,” Korver says. “An 82-game season is more of a grind than anything else I've ever been a part of. When I need it, I can imagine myself picking up and running that rock.”

Korver is up at 4:15 to take care of his crying daughter. Once Kyra falls back asleep, he lies there thinking about the difference between a misogi and a basketball game: You can’t lose a misogi. I may get really cold. I may get really tired. I may not know how it’s gonna work. There’s nerves, but it’s different than basketball. This is adventure.

As I lie awake in my motel room, waiting for my alarm to go off, my own nerves are frayed. I’ve intentionally not trained for what I’m about to do; I wanted to test my limits. I felt the same way before I hiked the Appalachian Trail more than a decade ago. Did that prepare me for this?

Parrish picks me up around six, buzzing from coffee. I ask about Alaska to distract us. “My home ski hill was 20 miles north of America’s northernmost stoplight,” he says. “I remember races so cold the lifts wouldn’t run.” Parrish was an elite racer but not quite good enough to make a living. Over the years, he worked as a concrete layer, heavy-machinery operator, and Internet marketer before becoming an artist. He aims to display his totem poles in the Guggenheim by age 40. The misogi sent the same message to Parrish as his art: you can do whatever you want.

On the boat, Kearin hands me a few of his coffee-flavored chia bars as we bounce toward the Channel Islands. “I was never into organized sports growing up,” he says. “But I heard about the Sahara Race a few years ago and it intrigued me: half the racers fail! My wife was pregnant, but she said, ‘Do it now.’ ”

“It was the hardest physical thing I’ve ever done,” he says. He ran a marathon a day for the first four days and a double on the fifth. There was a victory lap around the Pyramids.

“When I got back, Elliott was like, ‘How’d it go.’ We sat down for a quick beer. Two and a half hours later, we were out in the parking lot talking about misogi. I was hooked.”

Arriving two hours later at the Coches Prietos anchorage, we put on our wetsuits and swim to the empty, perfect beach to look for large rocks. Within minutes, Korver thinks he’s found a keeper. “This is it,” he says, wading with the thing, his arms bulging. It looks far too big to me. But once I hold it in the water, carrying the rock seems… almost fathomable.

I start with Elliott, who isn’t taking any real precautions three weeks after going under the knife, and Kearin; they’ve found a slightly smaller stone. We gather at one end of the anchorage, in around eight feet of water. Elliott descends first and makes it maybe seven yards. Kearin goes a bit farther, rises, and treads water above the rock so I’ll know where to find it. My turn! Diving down, as the surf clouds the water and pushes me around, takes so much energy that once I’ve wrangled the stone into my arms I feel that I must refill my lungs instantly.

During my first few dozen attempts, I rise to the surface after a few yards and sputter something vaguely apologetic: “Guys, just, it’s not... Hold on. Shit.” Meanwhile, Korver carries the boulder greater and greater distances with seeming ease. Emerging after one carry, he yelled out, “Boom!”

For me, the first hour is an eye-stinging, lung-burning, pride-killing exercise in futility. The second hour, too. And much of the third. I get tangled up with the story’s underwater photographer at one point and nearly come to blows. Elliott accidentally rakes me across the face with the rock. Shortly thereafter I hit his shin. There are few words exchanged beyond: “Here... You got this… Good job.” Except I’m not doing a good job. I can’t seem to take a big enough breath. I’m often gripped with panic when I touch bottom and try to move. I can’t get traction. My gloves feel too large, so I rip them off. My goggles fog and I curse them. I bemoan my employment, my employer, my god.

Why, I ask myself repeatedly, don’t I just swim to the boat, get in, and say that I’ve pulled a muscle? It might be obvious, but it’ll spare me who knows how many more hours of shameful shuffling along the seafloor. I can “report” the story from Over There.

Finally, an opportunity to flee arises: we need potable water, and someone must swim to the boat to get it. I volunteer. But once I’ve quenched my thirst and had a snack, I return.

I don’t know if it was an underwater version of Stockholm syndrome or if layers of pain actually began to peel away, as Parrish said they would. But something funny happens once you’ve been in the grip of a painful ordeal for a certain amount of time. Namely, the body and mind—inured to the unwelcome task they’ve been set upon—mostly stop fighting it. Resisting takes too much energy. It cannot be sustained. And, gradually, in place of my instinctive resistance came an active kind of relaxation and acceptance.

That’s not to say that I was at peace down there, or in any way Zen at all. Far from it. But I did occasionally smile and chuckle as I descended and rose with the multimillion-year-old rock. I even gave it a nickname, Old Red. Red and I were going on a very slow journey, I imagined, to the netherworld and back. The fate of my girlfriend in Atlanta depended upon it.

It may sound like madness. But so do many goals: get your art in the Guggenheim, run your first ultra, set an all-time NBA record.

I began to go five and even ten yards. These were not Walter Payton scrambles, you understand, like Korver and Kearin’s insane 20-yard carries. They were, at best, the kind his backup could muster. But the guys cheered when I pushed hard. My muscle spasms came and went like sudden squalls. Thoughts of quitting ceased. I recall very little actual conversation, but at one point I think Kearin did say, “The writer’s killing it.” That goes up on the shelf with the greatest compliments I’ve received in my 33 years.

Four hours and 49 minutes after starting, we are done, in every sense. Elliott turns to me and says, “I thought for sure you were going to quit at the beginning.” The others agree. “You had that look,” says Korver, who tells us he worked even harder today than he did on his paddleboard last year. “You’re our brother now,” says Parrish, panting and seeming a bit deranged. I hear myself howl.

Back on the boat, we pose for pictures in the setting sun. “Life isn’t a movie,” says Elliott, pleased with our effort. “It’s snapshots. It’s so easy to burn a day. Why not make it memorable? Add fear and adventure and you’ve got a rich experience.”

“It’s this W—a win—you have in your back pocket,” says Parrish. “That can translate to somewhere else. You can say: ‘I have no idea what I’m doing now, but I know I did this crazy thing over here.’ ”

“The misogis have turned into my grind activator,” Korver tells me later. “An 82-game season is more of a grind than anything else I’ve ever been a part of. There are so many highs and so many lows. Days when I have lots of energy and days when I have none. Those are the days when you have to call on your grind mode. Find the Repeat button. Learn to relax in it. Maybe even learn to enjoy it. And when I need it, I can imagine myself stroking across the Pacific Ocean. Or picking up and running that rock.”

Before parting that night, Parrish suggests an idea for next year: going into the woods, felling a tree, and making tables on the spot. “That’s what happens when the Alaskan artist starts designing the misogis,” Elliott says. “It turns into arts and crafts.” Joking aside, Elliott knows there’s business potential here, but he’s hesitant to go in that direction. “It’s so pure,” he says. “I want to keep it that way.” Meanwhile, he says that more pro athletes—including last year’s NBA Finals MVP, Kawhi Leonard, of the San Antonio Spurs—have expressed interest in trying a misogi.

In the months since my own challenge, I’ve had trouble articulating exactly what happened to me down there with the rocks. My answers sometimes sound like the dubious fruit of a vision quest or a self-help seminar: Yes, my sense of my limitations has been expanded. I could even say they’ve evaporated at times. But the truth is, most -succinctly: my lungs and my balls feel twice as large.

Most people aren’t ready to hear that sort of thing. My mother wonders, worriedly, if “that doctor guy might be full of shit.” All I can say for sure is this, Mom: anything is possible.

Charles Bethea (@charlesbethea) wrote about Lonely Planet CEO Daniel Houghton in April 2014.