For the first time, I see doubt creep into Zuqueto's eyes and freeze his feet. Zuqueto is a two-time world champion jujitsu fighter and a professional free diver who needs only a knife and a lungful of air to battle sharks. I've watched him scramble 40 feet up a coconut tree faster than I can run the same distance. I've also seen him lift a man twice his size and slam him down like a sack of cement. But now Zuqueto is on the verge of being defeated by a wooden pole lashed between two trees in the Brazilian rain forest.

The pole, as thick as his arm, parallels the ground at roughly eye level. A man is standing on it, balancing like a tightrope walker, hopping from one bare foot to the other to amuse himself while Zuqueto sweats his options. He's been chasing this man for 20 minutes, sprinting around trees, leaping off boulders, and once even vaulting through the front window of a hut and back out through the rear without breaking stride.

"What are you waiting for?" asks the man on the pole. Before "you" leaves his lips, Zuqueto is flying straight at him, grabbing the pole with two meaty fists, pivoting a foot up and...losing his balance and falling back to the ground.

Zuqueto leaps again, and again, while the guy on the pole looks down with the thinnest of smiles. I've got you, big boy, that smile is saying. I've found your weak spot. Now I'm going to rip it wide open.

Then he winks at me, as if to say, And you're next, bud.

When Zuqueto finally steps back, thick fists on his hips, chest heaving in fatigue and frustration, the man hops down from the pole. His name is Erwan Le Corre, a 37-year-old Frenchman who may rank as one of the most all-around physically fit men on the planet. His last name sounds exactly like the French phrase for "the body" -- le corps -- and his appearance lives up to the advance billing: If he grew out his sun-bleached hair and traded the board shorts for a loincloth, he'd be a perfect twin for Tarzan. Le Corre isn't just strong and fast and explosive and nimble; he's an athlete whose opponents are everything he sees and whose arena is anywhere he happens to be standing.

I've just arrived at Le Corre's training base in the Brazilian rain forest. For the next 3 days, he'll be teaching me one of humankind's oldest, trickiest, and most indispensable physical disciplines. Le Corre calls it "Natural Movement" -- or "MovNat" in its French abbreviation -- and to explain what it is, he points at Zuqueto.

"This guy is in amazing shape," Le Corre says, speaking Brazilian Portuguese with an almost native accent. "He's strong and he has great endurance. But what happened here? All he had to do was get on top of this pole, and he couldn't. I can do it. Zuqueto's great-great grandfather could probably do it. At one point in time, just about every man alive could do it. But Zuqueto can't. And why? Because his body isn't smart enough."

A smart body, he explains, knows how to convert force and speed into an almost endless menu of practical movements. Hoisting yourself onto a pole may seem as trivial as a circus stunt, but if you're ever caught in a flood or fleeing an attacking dog, elevating your body 5 feet off the ground could mean the difference between safety and sorrow.

And with that one word -- "practical" -- Le Corre exposes a key weakness in modern exercise: Our workouts are domesticated, while the world out there is still plenty wild. In a pinch, can a man put gym-generated biceps and tank-tread abs to any real use? Could it be that our treadmill-running, elliptical-gliding, well-oiled Cybex world has turned us into show dogs who can't hold our own in the hunt?

"I meet men all the time who can bench 400 pounds but can't climb up through a window to pull someone from a burning building," Le Corre says. "I know guys who can run marathons but can't sprint to anyone's rescue unless they put their shoes on first. Lots of swimmers do laps every day but can't dive deep enough to save a friend, or know how to carry him over rocks and out of the surf."

Le Corre could rattle off dozens of other disaster and heroism scenarios, but standing still for 5 minutes has left him itchy. He interrupts his own speech to demonstrate what a smart body looks like in action. Launching himself into the air, he swings up onto the pole that stymied Zuqueto, and then twists his knees and swiftly rises like a surfer catching a wave. Then he proceeds to jump down, light as a cat, and mount the pole two...three...six more times, in each instance using his elbows, ankles, shoulders, and neck to create new climbing combinations.

"Being fit isn't about being able to lift a steel bar or finish an Ironman," Le Corre says, watching with satisfaction as Zuqueto finally makes it onto the pole and pumps a fist in the air like he's won his third world championship. "It's about rediscovering our biological nature and releasing the wild human animal inside."

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The best place to retrain that inner animal, Le Corre decided, is Itacare, a tiny village squeezed between the rain forest and the Atlantic Ocean. He wandered here from his home near Paris more than a year ago and instantly recognized two things: Itacare had everything he would need to teach MovNat and everything that the Master -- Georges Hebert -- would have loved.

In 1902, Georges Hebert was a 27-year-old French naval officer stationed on the Caribbean island of Martinique. On May 8 of that year, he was aboard a ship off the coast when an ominous plume began rising from Mont Pelee, the volcano looming over Saint-Pierre, Martinique's largest city. Sometime around 8 a.m., Pelee erupted, raining hot ash and sizzling rocks on the horrified population. Molten lava gushed down the slope and spread through the streets in fiery streams, igniting everything in its path. Swarms of pit vipers poured off the mountain to flee the searing heat, tangling in the feet of fleeing people and biting at their legs. In minutes, the Paris of the Caribbean had turned into an absolute hell.

Into this inferno plunged Hebert. Leading his troops ashore, he scouted out viable escape routes and waded into the panicky crowds, trying to shepherd them to safety. By the time the eruptions ceased, fewer than 700 people had survived, many thanks to Hebert's improvised rescue operation.

Hebert was celebrated as a hero, but he couldn't help focusing on all of those who'd been lost. When he returned home to France, he looked around and was dismayed to see how many of his country-people reminded him of the victims he'd watched die in Saint-Pierre. How many of these Parisians, he wondered, would be able to carry a child on their backs? Or trust themselves to leap over a 3-foot gap? Or take an elbow to the face but manage to keep their balance and continue running for their lives?

The modern world, Hebert believed, was producing hollow men who focused on appearance and forgot about function. At the same time, they stopped exercising with the wildness of kids and instead insulated themselves from risk. The cost, he felt, was far more destructive than they might think.

Motivated to do what he could to realign our fitness philosophy, Hebert convinced the French navy to put him in charge of conditioning for a class of its recruits. Using the recruits as guinea pigs, he incubated a system he called Methode Naturelle -- the Natural Method. Hebert preached a simple philosophy -- "Be strong to be useful" -- and focused on 10 essential skills: walking, running, jumping, walking on all fours, climbing, balancing, throwing, lifting, defending, and swimming.

Next, Hebert set to work on an outdoor training facility. He designed it to look like a giant playground, equipping it with climbing towers, vaulting horses, sandpits, and ponds. Scattered about were rocks and logs and long poles to be used for throwing, or balancing, or passing hand-to-hand while running, or anything else an athlete dreamed up at the moment. Hebert had only one firm rule: No competing. When you try to beat the other guy, he believed, you test the other man's weaknesses and not your own.

Within a few years, Hebert's "Be Useful" system was adopted by the entire French navy. In 1913, speaking before the French Physical Education Congress, he astounded them with the results of tests he'd performed on 350 navy recruits. On a rating system that scored performance according to strength, speed, agility, and endurance, French sailors ranked with world-class decathletes.

The time had come to take Methode Naturelle to the world. Hebert handpicked an elite team of trainers and prepared them to spread the word throughout Europe, Asia, and America. But before they scattered, the First World War erupted. Because of their superb physical conditioning and dedication to service, the men of Methode Naturelle were deployed in frontline positions against German troops armed with machine guns and poison gas. By the end of the war, the trainers were all dead or maimed. Hebert was heartbroken, but not surprised. Methode Naturelle was never about trying to live forever -- it was about trying to make a difference before you died.

Hebert himself barely survived his wounds and struggled to regain the use of one arm. When he sank into paralysis after the war, Methode Naturelle was all but forgotten, swept away by a world that wanted to pretend that danger was gone forever.

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At sunrise, Le Corre vaults through my window.

"Ready to play in the jungle?" he asks. "You're not afraid of heights, are you?"

"I'm not wild about them."

"That's because you never learned how to climb," he says. He vanishes back out the window, which is 3 feet from a half-open and perfectly functioning door.

Itacare is a legendary surf break, but with the first slants of sun just slashing through the rain forest, none of the village's gypsy colony of international surf bums has turned up yet. Le Corre and I shuck our shirts. By the time I look up, a group of men is emerging from the trees and surrounding us.

"Mais uma vitima!" one of them shouts: One more victim!

Le Corre glances around. He spots a bowling-ball-size rock on the sand. With a quick crouch, he scoops it up and snaps it with a sharp, two-handed throw straight at the man's chest. But instead of diving out of the way, the man stands his ground and deftly catches the big stone. He tosses it aside, raises a fist, and steps toward Le Corre.

"He's no victim," Le Corre says in Portuguese, as he and the man fist-bump. "He's a work in progress, like you."

Le Corre introduces me to Serginho while the seven other men pull off T-shirts and kick off flip-flops. When Le Corre first arrived in Itacare, he stumbled on the perfect band of collaborators: a small community of martial artists who make their base in the village to escape distractions and who earn their keep as surf instructors and spearfishing guides. Le Corre found that the fighters could help him hone his grappling and tumbling skills. In return, he taught them how to build strength, endurance, and agility.

Le Corre marshals us into a tight circle. We start passing a big rock from hand to hand. Le Corre adds another rock, then another and another until there are five in play and it's all I can do to move one rock out of my hands before the next is shoved into my gut. Unlike medicine balls, which always have the same, easily graspable shape, the unpredictable size and weight of rocks force you to focus intensely on grip and balance. Even though the rocks are turning slick with sweat and my arms are burning, I'll be damned if I'm going to be the first to let one slip. Luckily, just when I'm in danger of smashing my toes, Le Corre raises a hand for us to stop. I drop my rock, relieved -- until I find out what's next.

Each of us has to hoist another guy across our shoulders in a rescue hold, and race in and out of the knee-high surf. If there's a workout that's more nerve-racking than preventing a 220-pound Thai fighter from falling on his head, I don't want to know about it. Humans are heavy and lumpy and oddly balanced, forcing you to constantly adjust your posture, footing, handholds, and core. Keeping control of a body on your back, I soon learn, demands intense concentration and full activation of every muscle group.

Next, Le Corre has a pile of 6-foot-long driftwood poles at the ready. The other guys know what to expect and start trotting down the beach. As they pass Le Corre, he tosses poles to some of them. He tosses the last one to me, and then takes off on a run with his hands outstretched. I toss it back and he immediately flips it toward me again, this time a little ahead so I have to accelerate. We cross the entire beach this way, mixing up our throws, totally absorbed in our run 'n' gun until I notice that we're about to crash into the rocks. Without breaking stride, Le Corre flips the stick around, plants it in the sand, and pole-vaults up onto the boulders.

By the time I climb up after him, he's 20 yards away, scuttling to the top of a giant rock overhanging the sand. "The secret to a good jump," he says, "is a good second jump. Remember your springs..." and with that, he's sailing through the air. He lands 10 feet below with a deep knee bend, but instead of rolling or dropping to his knees, he bounces right up with a hop and tears off at a sprint. "Cats are running the second they land," he calls up as he loops back around. "If you do it the same way, you'll decrease impact and be ready to flow into your next move."

Le Corre had already schooled me in high jumps my first morning in Itacare. I know I can handle the leap, but still, the sight of all that empty air below gives me pause. Even Zuqueto has to think twice before launching himself off the rock.

"Caralho! Esse gajo e forte," I can hear Zuqueto say, which is a lot of respect to pack into five words. "F -- -! That guy is strong." The two-time jujitsu world champion and shark-fighting diver sighs as he watches the skinny Frenchman sail through the air.

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"This guy is really onto something," says Lee Saxby, P.T., a London-based physical therapist and the technical director of Wildfitness, an exercise program built around an evolutionary model of human performance. For years, Saxby had been teaching his clients that the key to overall health is a workout system that mimics the diversity of a hunter-gatherer lifestyle. When Saxby stumbled across a YouTube video of Le Corre (MensHealth.com/LeCorre), he'd found Exhibit A in the flesh.

"What impresses me most about that video is Le Corre's athleticism," Saxby says. "It drives me crazy that men think being in shape means being big. But the best athletes don't look like bodybuilders. They're lean and quick and mobile. Le Corre demonstrates real functional fitness -- the opposite of what they teach you in the gym."

Le Corre, in fact, could be one of the best living examples of what our bodies were originally designed to do. "Versatility was the key to survival, because early humans had to be ready for anything at any time," says E. Paul Zehr, Ph.D., a kinesiology professor at the University of Victoria and the author of Becoming Batman: The Possibility of a Superhero. "If your daily life is hunting and being hunted, at a moment's notice you might have to sprint, jog, throw a spear, scramble up a tree, hunker down, and dig. The specialization we enjoy today, be it as a marathoner or a tennis player -- even a triathlete -- is a luxury of modern society. It doesn't have great survival value for Homo sapiens in the wild."

Neither does a lonely lunch-hour jog on a treadmill. "We evolved to value the group dynamic, which is why it's far more beneficial to exercise as a team," says Frank Forencich, a trainer who studied hunter-gatherer tribes for his book, Exuberant Animal. "Among indigenous people, it's considered crazy to go off hunting by yourself. Working as a team is a way of protecting one another and trading hard-won knowledge. It's even become embedded in our DNA -- group activities have been shown to increase creativity and lower depression."

But Le Corre's most important breakthrough might be the way he's welded purpose and playfulness. When he jumps and tumbles and chucks stuff around, he looks just like a kid mucking in the backyard. Zehr believes that could be the way we're hardwired to work out. "You never see your dog running nonstop around and around in a circle for an hour," he points out. "If he did, you'd think there was something wrong with him. Instead, he'll chase something, roll around, sprint, rest, mix things up. Animal play has a purpose, and it's not hard to surmise that human play should as well."

"Most people see exercise as punishment for being fat," adds Saxby. "So instead of being a stress release, it's a mental burden. That's why I think what Le Corre is up to is bang on. If he can reverse the idea that exercise is punishment, it would be a great gift."

"Ready?" Le Corre asks from his perch 20 feet up in a tree. Before we can speak, he answers for us. "Sure you are. Let's do it."

After 3 days of double-sessions training, it's time for my going-away present/final exam. Le Corre has fashioned an obstacle course that will both test my jungle-man skills and give me a model for my own program back home. In keeping with his gospel of group dynamics, he has asked Zuqueto and another fighter, Fabio, to join me.

"The test," Le Corre says, "is to finish the course twice in less than 20 minutes." But it's not about speed, he stresses. Le Corre is convinced that 20 to 30 minutes a day is all anyone needs for a killer workout, as long as it's intelligently designed. By combining short, explosive bursts of running with lots of power work -- jumps, climbs, and deadlifts -- you can compress 2 hours of normal gym time into 20 minutes of constant motion.

He drops his hand -- go! -- and we're off, chasing hard on each others' heels. The course has 12 stations, all of them sequenced into a natural flow through the forest. We're springing up into trees, contorting through the branches, and shinnying down 15-foot poles. He has us hoisting heavy logs on end and flipping them, top over bottom, up a hill. He has us crawling around stakes in the ground and snaking on our bellies beneath an overturned dugout canoe mounted a few inches off the ground. Even a small cabin comes into play: He has us vaulting through one window and out the other.

The most ingenious thing about Le Corre's course, I realize as I finish the first lap, is how universal it is. Sure, it's a blast to horse around in trees in the middle of the Brazilian rain forest, but there isn't anything here that can't be approximated in a backyard or community park.

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As I approach the end of my second lap, I have only two obstacles left -- a leap from the porch and then a quick climb up a 20-foot pole braced between the ground and a branch high in a tree. I'm trying not to show it, but I'm on the verge of grinning with pride. Two days ago, my heart was in my throat before every jump. Now, after just 72 hours, I feel unstoppable.

Naturally, that's when disaster strikes.

When I stick the landing off the porch, a red-hot knife jabs into my spine. My back is seizing up so badly I can't even stand straight. I should have known I was pushing my luck -- 14-hour plane trips always leave me tight as a banjo string. So that's it, I'm done...until I remember Le Corre's motto.

"Smart body," I remind myself. "Use your smart body."

I take hold of the long pole that extends on a 45-degree angle up into the tree. Gingerly, I hook one foot up, then the other, until I'm hanging upside down from the pole like a sloth. I tighten my grip and...wonder what the hell to do next.

"Any ideas?" I ask Le Corre.

"Claro," he responds. "Sure. Lots of them." It's an excellent teaching moment, the perfect opportunity for him to dig into his mental archives and pull out a few of the innovations he's compiled over the years. I've seen them in his notes, lots of stick-figure drawings dating back to Georges Hebert's original field experiments. Le Corre has a ton of wisdom to pass on -- but instead he just stands there, arms folded across his chest. He doesn't give me a clue...or even a smile.

Neither do Zuqueto or Fabio. They've become converts to the essence of Le Corre's philosophy: When that volcano blows, you have to be ready to go on your own. You won't have a spotter to ease the bar off your chest, no volunteer handing you water at the 20-mile mark. A group dynamic may be our natural impulse, but in a pinch, count on being alone. The only thing you can rely on is the ingenuity programmed into your system by 2 million years of hope and fear.

My hands are slick with sweat and starting to slip off the pole. Just to secure my grip till I can think of something, I slowly start swinging from side to side, building up momentum. At the top of every swing, my body is suspended for a second in midair. That's when I move my hands and feet farther up the pole, gliding higher and higher with almost no pain or effort.

"Ah, you learned my secret!" Le Corre calls from down below. "The best secret of all -- your body always has another trick up its sleeve."

It's hard to tell from upside down at the top of a tree, but I think he's smiling.

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