Turning 40, I needed a good alternative to financing a sports car or having an affair. My wife agreed. Forty is a simple actuarial milestone, but it kicks up existential waves in the inner ear. More life is likely now behind me than ahead of me.

I needed something on the horizon that was physically challenging and involved friends. I decided to try a Tough Mudder, a 12-mile obstacle course that takes runners under barbed wire, over fire, across monkey bars, through ice water, and into live dangling electrical wires, all along the muddy way.

Just four years since the first one, more than 1.5 million people, average age 29, have completed a Tough Mudder. Outside magazine has called it the fastest-growing sport in the States; this year, 55 events are scheduled in 15 countries. Other obstacle-and-mud events are exploding in popularity. What started as a sport for fringe athlete-masochists is now an industry generating hundreds of millions of dollars annually, and seen on the Today show and Wheaties cereal boxes.

Late one night a week before the challenge, I noticed the worn brown spine of John Bunyan's The Pilgrim's Progress on our bookshelf. My family was asleep. My legs were leaden from doing squats that morning. I sat down to read again about Christian setting out on his metaphorical adventure of the spiritual life along winding trails, through the Slough of Despond, with tempters and friends and pitfalls along the way.

Now, after my own adventure, I think that Tough Mudder is The Pilgrim's Progress for an intensified age.

After checking in, our seven-person team walks up to a seven-foot wooden wall you have to clamber over—just to get into the starting area. My hand slips, and I barely make it over. Not a seeker-sensitive welcome to the event.

Some 10,000 people will attempt this course on a central Florida ranch today. About one of every five runners who start a Tough Mudder fails to finish. Our team, made up of friends and friends of friends, is nervous. We're in the first wave.

Upon landing on the other side of the wall, we are huddled with a couple hundred people for a mix of Braveheart pep talk and revival service to an insistent Eminem backbeat.

"Can I get a Hoo-rah?" Pastor MC Drill Sergeant (I'll call him) booms out.

"Hoo-rah!" hundreds shout back as he prepares us for what's ahead. It's fun and inspiring: you're going to push your limits; you might overcome, individually, together, heroically.

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But Marine-like Hoo-rahs? The planners have raised more than $6 million for the Wounded Warrior Project, a nonprofit that helps injured military service members readjust upon returning home. Some of the veterans do the course themselves. But there's also a guy nearby dressed in a full-body Scooby-Doo outfit. This is a morning outing for him and the rest of us, then back to our lives. Marines we are not.

One thing you learn when you work with people in poverty is to be skeptical about appropriating, at a discount rate, the suffering of others—in this case, people wounded in battle—for our own meaning. But right now there is little time for reflection.

"Can I get a Hoo-rah?"

"Hoo-rah!" we roar.

Everyone in the group is jumping, hands up, jacked up. Me too! The cost will be part of the reward—Dietrich Bonhoeffer as fiery football coach. This is not a race but a challenge, one of the core values we repeat collectively as liturgical pledge.

Music pumps. Nerves jangle. Hearts speed up to the beat.

Looking around at friends and strangers—some in sleek Under Armour gear and some in tutus, some shirtless and perfectly toned and some who, well, seem unlikely to make it—I realize that each of us is on a Pilgrim's Progress seeking meaning and community.

The preacher sends us forth, and I high-five him as I run past.

The Phoenix

We run in a pack down a trail that takes us through fields, around trees, beside canals. We jump into a three-foot-deep watery ditch, then scramble over a dirt pile. Our thighs are now slathered in mud. We arrive at an obstacle called Kiss the Mud—50 feet of low barbed wire. As I start to crawl, my shirttail snags on the first barb. I reach back to unhook myself. Friends let me know when I clear the final one.

We round the path to the Phoenix, named for the mythical bird that went up in flames every few centuries, only to rise from the ashes as a new, young bird. Some early Christians adopted the symbol as a foreshadowing of resurrection. The Tough Mudder Phoenix requires us to crawl through a smoky tunnel, scramble to our feet, sprint up an incline, jump over two feet of fire, and drop five feet into chest-deep water below.

It's not too physically demanding, but it is exhilarating. A Tough Mudder staff member took me on a tour of the course several days before the race. As we jostled in an all-terrain cart past this obstacle under construction, he said, "It's fairly new—and you get great photos!"

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Indeed you do. A modern-day pilgrim gets plenty of help from a companion named Self-Aggrandizement, who is always whispering that nothing is worth doing, or even real, unless you can post a good photo of it.

Mud Mile

We slog through a canal of waist-high water and squishy mud that can swallow your foot. Called the Mud Mile, it might as well be the Slough of Despond. The first wave of people is spreading out. About a quarter of them are women; minorities are in the minority.

I had been embarrassed to tell my friend and colleague Enel about preparing for this. Enel and I work for a nonprofit focused on education for schools and churches in Haiti. We've been in daily or weekly contact for ten years. Since my wife and I moved back from Haiti to the United States, my decisions about what to buy and where to live have been shaped by knowing that Enel will visit our home and ride in our car. Perhaps a more spiritual person would just evaluate such decisions according to a Christ-tuned conscience. I find friends like Enel a helpful stand-in. Let's call him Accountability.

After my explanatory powers in Creole were stretched describing Tough Mudder, Accountability said, "Interesting. It's like life: there are times you just have to persist and endure, then obstacles you have to overcome. Then you have to keep going." He was amused, wanted to hear how it went, and burst out laughing when I invited him to join us. It was a kind response to the fact that many in our country are affluent enough to pay for extra physical and psychological challenges in our lives. In Enel's world, the challenges are typically free and unwanted.

Funky Monkey

Hangin' Tough is an obstacle with eight rings like those used by male Olympian gymnasts. Our task is to swing, like Spider-Man or monkeys, across a 20-foot water pit to the other side. I hold a ring on the platform. Deep breath. Swing out to grab the next one. Down I fall so fast, there is no story of struggle. It's a failure of strength and also will, I can't help thinking. It's an instant confession of weakness as I splash into the murky drink, which you'd best not sip.

Later the Funky Monkey bars loom with more importance than I care to admit. Until a few months ago, I could only go three bars. I trained at the playground, where my young daughter and son would cross all the way without effort, then taunt me as I tried to cross while bending my legs up.

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I really want to traverse all 24 bars. It's possible but not probable. The bars are slippery. People grunt, succeed, splash down all around. I slip … recover … strain … slip … and make it!

Exercise is an act of stewardship with two primary aims: to care for our bodies so we can give them more readily to the loving service of God and neighbor, and to enjoy our bodies as the divine gifts that they are. Of course, our bodies can also fail and betray us—I'm partly doing the Tough Mudder because of my family history of heart disease. Vigorous exercise should raise my good hdl cholesterol. I need my body and spirit to help each other along.

"Train yourself in godliness, for, while physical training is of some value, godliness is valuable in every way, holding promise for both the present life and the life to come" (1 Tim. 4:7–8, NRSV).

How hard it is for our society to hit that mark: "physical training is of some value." Look around, and fitness seems like it is either of no value—our obesity rates, our profitable corporations peddling junk (Dr. Pepper is my favorite)—or of supreme value, as we gather reverently around the TV to watch football or idolize muscle tone at Planet Fitness.

When my feet touch down at the end of the monkey bars, it feels like landing on gratitude, for the simple joys of health and effort. And the splash on the first ring reminded me that exercise, especially as one passes age 40, can surely be a spiritual discipline for nurturing humility.

Over Walls

My friend Companion (whose real name is Jonathan) is on our team, and we just met. We have to go over four walls on the course. At the first one, I find I'm not strong enough to pull myself up and over. Companion offers his shoulder for me to step on, helping to hoist me over. He does it again at the next wall.

Miles later at a 9-foot-high wall, Companion offers his shoulder again. When I look down, he is grimacing, rubbing his shoulder where my dirty cleat footprint is. He then climbs over the wall himself.

The next wall comes a few steps later. I help someone who doesn't have a teammate. Then Companion offers me his shoulder again. "Greater love has no one than this: to lay down one's life for one's friends" (John 15:13). Moments like this help explain why Tough Mudder is growing—and why church groups are doing it together.

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For the past months, while I've been out running and doing burpees, people in Syria have been slaughtered. Perhaps at the very moment I was carrying a sandbag through the Sack Up obstacle, a Syrian father was running with his child in his arms in search of safety. This very morning, a mother in Haiti got up at 4:30, as she does every morning, to carry 30 pounds of vegetables in a basket on her head down a mountain, to sit on the concrete in the sun to sell them, then to buy provisions (not enough, never enough) to carry hours up the steep climb home.

If not renounced, privilege must be regularly confessed. Then it must be carried—heavy, complex—and given away again and again. When I give myself, like Companion, to helping people over obstacles that they can't surmount on their own, I find firmer footing that feels like a pilgrim's path.

This relates to how I received the benediction from Accountability to do this event. I felt like I was carrying less guilt into it—as long as I was also carrying my weight in the more important challenges we face in our work together. Which leads to two questions for evaluating whether we're keeping pursuits like the Tough Mudder in the right perspective: Do our entertainments lead us in joyful and even silly ways to feel lighter—so that we can keep stepping under the heavy loads of mourning with those who mourn the most, and can keep energized for serving others? Or do our entertainments merely sedate us in our failure to love others as we are called to?

Arctic Enema

Nine miles and 15 obstacles in (the details, heights, and distances get a bit fuzzy at this point), we jump into the Arctic Enema, which requires you to submerge yourself entirely in a container full of icy water. The cold water shocks your breath away. You climb out of the frigid baptism on the other side.

Spartan Race is a competing obstacle event also quickly growing in popularity. "We came up with this idea to create a race," says the introductory video. "And during that process, [the participant would] become a new person."

Ten months ago in my first workout to prepare for this, I had made it 9 minutes into a 40-minute session. For the next 31 minutes, I lay on the grass as trees spun above me and my near-vomiting stomach. The trainer, Beth, hadn't expected me back. Now as we continue running on winding paths past palmettos, I'm grateful for the ache of every workout she led, for every extra mile I ran. Likewise, an important part of discipleship is the discipline of imagining the transformation and gratitude we will experience farther down the trail.

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I'm now walking with a friend whose legs are cramping. Up beside us jogs a guy we'll call Discouragement. He is barefoot and wearing a tiny Speedo and a fuzzy-bear hat.

"I don't even like Tough Mudder," says Discouragement, who has paid with money and effort to be out here. "It's not even hard."

His words could deliver a defeating blow to someone already limping. But from now on when I hear Discouragement's voice in my head, I'll try to picture it in this Speedo and hat. Laughter is a wonderful companion to discipline.

Electroshock Therapy

After 12 miles we arrive at the last obstacle, Electroshock Therapy, which involves running through live electrical wires dangling overhead. I'm pretty sure when signing the lengthy tiny-print Tough Mudder disclaimer, we renounced any right to prayers of safekeeping.

I take a few shocks and my right triceps muscle tingles as I turn to watch friends come through. Chris almost makes it when a shock knocks him flat. Pushing himself up, he's shocked again, and his face plants into the mud. A gasp comes from the couple hundred people who are watching.

Chris crawls out. I put my arm around him. He's dazed.

The seven of us walk the last few steps 3 hours and 20 minutes after starting. At the finish line, each of us is handed a cold beer. If this is a last temptation, I fail. Nothing could taste better. With full physical satisfaction, we sit on the grass and peel off mud-caked shoes and socks.

"The man called Jesus made mud, spread it on my eyes, and said to me, 'Go to Siloam and wash'" (John 9:11, NRSV).

Sprint and marathon, slog and soar, alongside Discouragement and Self-Aggrandizement and Companion: this is the pilgrimage of faith. Mud splatters all over, and we seek cleansing in dirty water. Silly as it might seem, all my preparation and these 12 miles might just be another way of straining to hear:

When you pass through the waters,
I will be with you;
and through the rivers,
they shall not overwhelm you;
when you walk through fire
you shall not be burned,
and the flame shall not consume you.
Because you are precious in my sight, and honored, and I love you.
(Isa. 43:2, 4, NRSV)

This Tough Mudder experience is so thoroughly physical that I experience it as profoundly spiritual. We Kissed the Mud (confession) and were dunked in an Arctic Enema (baptism). Now we're to keep pressing forward together in the soaring hope of the Phoenix (resurrection)—our discipline, bodies, and friendships strengthened. Because yes, each day our pilgrimage brings dirtying stumbles, and, yes, each day death steps closer. But the beautiful, ridiculous grace is this: life abundant steps closer too.

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Kent Annan is codirector of Haiti Partners, a nonprofit focused on education in Haiti, and author of After Shock and Following Jesus Through the Eye of the Needle (InterVarsity Press). He wrote our September 2013 cover story, "Chaos and Grace in the Slums of the Earth."

Special invitation for Chicagoland readers: Kent is training for the Spartan Race on September 27, 2014, in Chicago. Contact him by Twitter if you're interested in competing with him in a group: @kentannan.

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