Matthew McConaughey is creeping through the Costa Rican jungle, wielding a machete to brutally slash through dense swathes of vegetation. His clothing is drenched in sweat—not so much from the exertion but distress. He’s alone. Scared. Yet also energized. “The first sound you hear, you think everything that moves is a gator, a wild boar, a jaguar,” he says in his signature Texan drawl. He’s equipped with only his “lucky green headband, a shitload of insect repellent, and a headlamp for a light source,” he says. “Your adrenaline is pumping because you don’t know what to anticipate with the next step. Every movement is like a new, four dimensional ‘Oh, shit!’ ”

Is this perilous, late-night trek part of a big-budget action flick? Nope. It’s just the actor on vacation.

McConaughey recounts the experience as we walk a more urbanized trail— Magazine Street in New Orleans, where the jungle brush has given way to boutiques and eateries. Despite the blazing sun and a slight afternoon breeze, he is utterly at home. When he was growing up in Longview, TX, McConaughey’s mother always told him, “If it is light outside, you must be out of the house.” This partly explains why he prefers outdoor workouts (jungles and trails) instead of training in a gym, and why for years tabloid paps have snapped pics of his lean, muscular, and shirtless physique running, running, and running some more—usually on a beach. “It’s always been a lifestyle,” he says. “Then it became something that was like, ‘Hey, it’s also good for my job.’ I’m not a professional athlete, but I have a job where I like to look good and be as healthy as possible.”

Today, McConaughey strives to share his love for life and eating right. It all fits under his mantra, “Just keep livin’,” which isn’t just his personal philosophy—it’s also the name of his foundation: j.k. livin (“Ain’t no ‘g’ on the end ’cause life’s a verb—you with me?” he says). He founded it in 2005 to encourage children to make positive and healthy changes in their lives by getting more exercise and making smarter meal selections. He’s been known to bring in chefs to show families what they can do with a bag of rice, fresh fruit and vegetables, and meat instead of eating burgers every night. He’s even partnered with the NFL’s Play 60 initiative to encourage kids to be more active. The foundation also celebrates the life lessons (patience, healthy thinking, optimism) extolled by McConaughey’s father, Jim, who died in 1992. Those virtues also inspired McConaughey’s record label (j.k. livin), to which he has signed reggae singer Mishka, one of his favorite artists. “I do believe in people,” he says. “I do believe there are solutions. I believe there are ways to rebuild, rehabilitate. That doesn’t mean it happens. I’m just saying I believe that everybody has the potential to do it.”

McConaughey is 41 now, and he knows fitness is about more than just looking good. It’s about being able to keep up with his children (son Levi, 2, and daughter Vida, 1) without gasping for air. It’s about transforming his body for roles, whether he’s playing an athlete (Angels in the Outfield), cop (Lone Star), groom-to-be (The Wedding Planner), dragon-slayer (Reign of Fire), or litigator, as he did in this year's film, The Lincoln Lawyer. Depending on the gig, his weight swings from 176 to 194 pounds. On the day we meet, he’s at 186, his physical peak. “Matthew can do hundreds of pushups, and he’s mobile like a yoga person,” says his trainer, Peter Park, whom McConaughey met through fellow Texan Lance Armstrong. Yeah, that Lance Armstrong. “His fitness is through the roof. He’s not like Lance in aerobics, but he can hold his own.” (Of course, Matthew had only this to say about his occasional runs with the seven-time Tour de France champ: “You quickly learn what the back of his jersey looks like.”)

Find out how to train like Matthew McConaughey

When he's not prepping for a role, McConaughey trains with Park at his Malibu home. A typical day might include pullups on the kids’ swing set, followed by sprints in his backyard, pushups, one-legged squats, and finally kettlebell work in the driveway. He then takes his road bike out for several miles. “He likes challenging, almost gymnastics-type stuff,” says Park, whose clients include Armstrong, L.A. Laker Derek Fisher, and another MF cover guy, Rob Lowe. “He’d be bored stiff going into the gym and doing one of those basic workouts.” One favorite exercise: picking up a 45-pound dumbbell, a rock—whatever’s around—and holding it for 15 minutes. Try it, he dares you. “It’s not as simple as it seems,” McConaughey says, as he acts out the workout with an invisible weight. “You shift the weight from high above your head, in your right arm, then your left, then rest it on your shoulders, adding more weight to your back, then your legs. You get a full-body workout just by finding out how many positions you can manage without having to set the weight on the ground. You also discover the stronger and weaker spots in your physique.”

McConaughey says he was in the best shape of his life when his workout was at its simplest: 200 pushups and 1,000 crunches a day. It didn’t matter how many he did at a time, he says, just as long as he got ’em done in a day. A break in a meeting? Drop down and do 20. Every time the Washington Redskins, his favorite team, scored as he watched on television—another 20. Today, he takes a somewhat simpler approach. Now, his hour-long daily workout might be a session with Park or he might just follow Levi’s every step on the beach. “You’re playing goalie,” he says of those treks. “You’re moving around, keeping up with him. And he wants to get outside all the time. He may not cover more than three square feet, but he’ll climb a bunch of stuff and dig a bunch of holes and it’s nonstop.”

His workouts can become as mental or spiritual as they are physical. He once traveled to Africa for 21 days and was challenged by a village’s champion wrestler; he battled him to a bloody draw. He also went cave running in the mountains next to Real de Catorce, Mexico. “If you can be mentally stimulated by the workout and find out how to get through it, it’s more fun,” he says. McConaughey recalls a trip to French Polynesia with his live-in girlfriend and the mother of his children, Brazilian model Camila Alves. “We went up to 3,000 feet and I had on hiking shoes and I was all set up and ready to go and she was wearing Havaianas sandals and a white skirt. I came down to the bottom of that hill afterward and had blood on me, muddy as all get-out, and that girl didn’t have a speck of dust on her.”

McConaughey’s active lifestyle is matched by his love of healthy food. There’s a limit, though, to all that good eating. As our MF photo shoot wraps, the actor tries to figure out where to buy the best shrimp po-boy, his reward after five weeks of filming his next movie, Killer Joe, a dark comedy. “You can’t put me in front of a buffet line and tell me to eat right. If it’s there, I’m going to fill that plate up,” he admits.

Still, McConaughey says his clan eats healthy whenever possible. He and Camila do their own cooking, often with fresh ingredients from their backyard garden. For a snack, Matthew might eat a red pepper or an avocado, which quells the urge for chocolate. Come mealtime, he usually allows himself unlimited amounts of salad, topped with a dressing made with white vinegar, honey, Dijon mustard, shallots, and garlic. He rounds out the meal with brown or Indian rice, plus a touch of pickled pepper sauce. For protein, the family may have grilled fish or chicken breasts four days in a row, but homemade sauces and seasonings from three different continents give the main course distinctive tastes.

And despite his busy schedule, McConaughey is also sure to make certain he always gets in plenty of time with his loved ones, particularly the comely Alves. After years of being the “sexiest man alive” bachelor, he says he’s finally found the woman of his dreams. “It’s all working out good, man,” he says. “Working out real good.” The timing just had to be right, he says.

And now, it is.