Crushed by exhaustion, you may dream of a competitor's head morphing into a Pokémon-like demon — and then open your eyes and still see it. The next day, you will quit the race.

To fill your queasy stomach during your third 112-mile bike ride, you will discover the best way to eat a sausage-and-egg sandwich: Shove it in your mouth and let it slowly dissolve.

After 500 miles on a bike, 10 in the water, and more than 100 on foot, it will make perfect sense to grab a branch and a broomstick in a desperate bid to propel yourself — like a giant mutant insect — the last 31 miles. It will not be enough. You will collapse on the road.

Seasick, miles into the swim, you will vomit. Twice. Neck cramps will attack so fiercely on the bike that your head will slump. You will go cross-eyed and nearly crash.

You will swear bugs are crawling over your face, even when they are not. The cracks in the road will form smiley faces. None of this is real — but it is 3 a.m., and you have dozens of miles still to run.

All that misery and more menaced the competitors who had decided, for their own unfathomable reasons, that a single Ironman race was not enough. They had entered an endurance event called the Virginia Quintuple Anvil Triathlon — five Ironman-length races, totaling 703 miles of swimming, biking, and running, over five days.

All the legs were done in confined loops (30 laps in a section of the lake, 101 laps of a more-than-5-mile course for the bike, and 75 laps of a nearly 2-mile course for the run) at Lake Anna State Park in Virginia's Spotsylvania County, earning the course the moniker "squirrel cage."

The competitors — several of whom have formed a tight, family-like circle, having seen one another often at these kinds of races — were a mishmash of the superfit and the merely fit, military veterans (including a couple of former commandos), driven professionals, and simple thrill seekers, who found plenty.

Most were middle-aged, most had grown children who would not miss them much in the long hours of training, and most had supportive spouses and family members — in some cases triathletes themselves.

Some of those family members came to watch their loved ones destroy their bodies, if not their minds, for nearly a week because...because...why? "If you have to ask," more than a few racers replied, "you will never know."

You may have heard that idea expressed at, say, the regular old Ironman triathlon, which is normally considered the Mount Everest of the sport: a 2.4-mile swim, then a 112-mile bike ride, and then a marathon (26.2 miles) in the heat of Hawaii. If you could finish it, you were, well, an Ironman (or woman).

People began flocking to the challenge. Races popped up on every continent except Antarctica.

The first Ironman was in Hawaii in 1978, with 15 competitors. Today, there are 140 races to choose from, drawing 260,000 competitors.

But once you have swum 2.4 miles, biked 112 miles, and run 26.2 miles in a day, why stop there? As early as 1984, a double Ironman race was held in Alabama. And then a triple. And then a quintuple. And then a deca (10 Ironmans in 10 days) and a double deca, and you see where this is going.

Wayne Kurtz, who is considered the godfather of the so-called ultratriathletes, and seven others did 30 Ironman-length races in 30 days in Italy in 2013. He wrote about it in a book called Stronger Than Iron.

"With this kind of test," he wrote, "these athletes were not racing for money or fame but purely to discover what is possible in terms of endurance limits." How did it go? "I was hit by a car three times," Kurtz said in an interview. "It was a zoo. We're lucky nobody died."

One of the more popular races is the Quintuple Anvil, which grew to 16 competitors this year from seven in 2013, its inaugural year. Double and triple versions are held at the same time. (By the time you consider a quadruple, you might as well just do a quintuple. That is the mentality here.)

"Anvil" is a tongue-in-cheek spin on "Ironman," which is run by a large corporation fiercely protective of its trademark and not keen on letting other races use it. Competitors may choose one of two ways to mete out their self-flagellation: Do one Ironman-length triathlon a day for five days, abiding by a 17-hour cutoff, or do all of it continuously — a 12-mile swim, followed by a 560-mile bike ride and a 131-mile run — stretched out over 5½ days, broken up however you wish.

The 1-by-5 variant means you can get a longish night's sleep, but you have to get up for a 7 a.m. start every day — a fitness nut's Groundhog Day.

The continuous version usually involves a fair amount of sleep deprivation, in particular to get the long bike and run legs done. This is the fitness nut's Walking Dead: By the end, the mind is shot from exhaustion, and the legs and feet have taken so much punishment that hardly anybody is doing much running.

My own triathlon experience has been limited to a few "sprint" races of short distances, some Olympic-distance races (a swim of just under 1 mile, a 24-mile bike ride, and a 6.2-mile run) and one half-Ironman (1.2-mile swim, 56-mile ride, 13.1-mile run).

The half-Ironman, done in the tropical heat of Panama, left me staggering at the end and had me pretty sure that I had found my limit — and it wasn't happy to see me. Just beyond the finish line, there was an ice bath, which I felt like moving into permanently.

When I told this to Shanda Hill, who ended up one of the top finishers at the Anvil, she smiled and, with the evangelical fervor common among the racers, started pushing me to at least do an Ironman-length race. "It's all mental," Hill, 34, said, "and I am living proof."

By that, she meant that she had not devoted long hours to swimming, biking, or running. But she did spend a lot of time in the gym and was also fit from a youth of championship BMX racing, a pursuit that ended several years ago when she was hit by an SUV while riding a bike home.

She began running after that, moved up to ultramarathons, and before long was doing her first Ironman, in 2014. Then came a double race, and by her logic, if you are going to move up to a triple, you might as well just do the quintuple.

This was her fifth triathlon overall, and like many of the other athletes, she would insist that endurance triathlons had as much — if not more — to do with the limits of the mind as with those of the body.

Lisa Wei-Haas, who did a double, said, "Shorter triathlons are about pain. Endurance triathlons are about suffering. How much suffering can you take?"

Facedown on a cot, near midnight in the middle of the race, Will Turner had a massage therapist kneading his muscles, trying to coax some life into them. He was, at 58, an Ironman veteran who last year moved up to multiple-distance races by doing a double Ironman-length race.

He believes in big dreams, he said, and he dedicated his entry to his recently deceased mother. This race, the continuous Quintuple Anvil, would also be a test toward a bigger goal: 60 Ironman-length races, one every six days, when he turned 60. The test was not going well.

"I have been hanging out in the pain cave," he said.

Like other racers, Turner had a group of people attending to him, although as a resident of nearby Richmond, he had more than anybody else.

Limited medical assistance is permitted, too. A doctor and a nurse dispense ibuprofen, pop blisters when necessary, and even give shots of lidocaine to ailing tendons (a small dose that is meant to get a faltering competitor moving and does not last long).

To qualify, a competitor must have finished at least a double Ironman-length race, yet here was Jerome Libecki, 46, doing his first-ever triathlon. He had sort of slipped into the race — although he had done other endurance events, he'd needed a friend to persuade the race director to let him in.

His triathlon inexperience showed: About 300 miles into the bike leg, after a friend took a harder look at his bike, he realized he needed to shift into a higher gear.

By the "run" — for him and many others, it eventually slowed to a walk — Libecki was the one who hobbled on like a giant insect with makeshift crutches.

"This is the last thing I figured would happen," he said at 3 a.m., panting and sweating. But still he vowed to go on.

Even in the grip of exhaustion, there was a thirst for competition. Libecki and Turner, in their stooped gaits, still eyed each other as they passed, if in a last-man-standing kind of way.

People race to win, after all. And as if the physical demands of such a contest were not enough, some resort to psychological warfare. They misinform one another about whether they intend to nap, or they press on when they see a rival catching a snooze. They burst into a sprint when they see another competitor walking. Some methodically plot when to give their all and when to hold back.

Dolph Hoch IV, 52, a former military sniper, won the one-per-day quintuple division in a time of 74 hours 54 minutes 17 seconds, beating five other competitors (including two who quit). Unlike the other racers, Hoch conserved enough energy to complete his Day 4 (14:25:04) and Day 5 (14:46:31) races faster than he had done Day 1 (14:59:21).

"The first day, I was getting lapped on the bike," he said after the race, his thighs now "screaming." "Fifth day I had the fastest split. They had no idea I was saving my spin." (In my estimation, he also won best food trick, as the one who let the sausage sandwich dissolve in his mouth.)

The most grinding competition, however, was between David Jepson and Johan Desmet.

It was not quite a Rocky-like spectacle, but with Jepson, 40, looking to be falling apart at times, it did take on that feeling. At a rest stop, he threw down his bike helmet in frustration over cramps that had left him unable to hold his head up and nearly led to a crash.

But with reassuring words from his wife, Jepson regained his footing on the run despite a multitude of maladies: a "golf ball–size" blood blister on his foot he eventually popped, a shin splint, ankle tendons so sore they needed to be stabilized by duct tape, and bruising and chafing on the bottoms of his feet that made every step searing. Running was not much of an option anymore.

Desmet, 49, who is Belgian and a marathon runner, kept up an efficient gait for a good amount of the run and rarely complained about his ordeal despite the blisters and sores on his feet. One of them, a race nurse concluded, was from the bite of an insect that had gotten inside his shoe.

"You're not drinking enough," interrupted his wife, Helene, who served as his only crew member, handing him water during a late-evening break.

"You always say that," he said, taking a sip. Helene was ready for the race to be over. And so was he. After six years of ultra-racing, he was planning to pursue other adventures. "It's a pretty selfish sport," Desmet said. "She's been putting up with this for close to seven years."

In the end, Jepson won the continuous division with a time of 104:47:39. Desmet, still on the course, realized the best he could do was second place.

"I am going to be first loser," he cracked.

Excerpted from an article that originally appeared in The New York Times. Reprinted with permission.