After you’ve eaten like a cave man -- focusing on meat, veggies, fruits and nuts and foregoing dairy, grains, refined sugar and anything processed -- what’s next? Working out like our Paleolithic ancestors.

Paleo fitness -- also know as natural movement, primitive movement or primal fitness -- eschews elliptical trainers and free weights. Instead followers scramble around in trees, power lifting rocks and logs.

Shape Magazine named it one of the top 13 fitness trends to watch in 2013; Time calls it “the next big thing” in fitness. Outside magazine simply refers to it as “the workout that time forgot.”

Even when there’s no saber-tooth tiger or woolly mammoth to hunt down, the goal of the cave man workout “is to perform practical tasks, physical actions that you would perform in the real world, both in day-to-day and challenging situations,” says Erwan Le Corre, who founded the MovNat fitness system in 2008.

Like, say, chasing down a bus or cab instead of your dinner.

“People … perform basic human movements such as squatting, kneeling, stepping, balancing, crawling under an obstacle, jumping over another one, then lifting and carrying an object -- or someone -- over a distance, and many other movements,” Le Corre says. “Instead of plunking people in gyms and have them do boring repetitive workouts using machinery and trying to isolate muscles, we have them move a lot, to move in many ways they used to when they were kids.”

Most modern fitness programs focus on muscle-isolation and cardio-conditioning. But the body doesn’t work in isolation; it works synergistically, as a unit, he says.

“To be healthy, you need to move frequently and ideally, you need a variety of movement patterns, like we do when we are young children,” he says. “The more varied the movements, the better for health, fitness and resiliency.”

Darrell Kirk, 51, didn’t join a formal paleo fitness program, but came up with his own natural workout based on things he used do as a kid.

“I've always admired the way children run and play for hours and thought this would be a great exercise program,” he says. “It’s fun and it’s healthy.”

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Kirk’s workout involves everything from “roughhousing with his son” (especially swinging and spinning him around) to stand-up paddle-boarding to obstacle courses in the woods to running the huge flight of stairs near his Seattle home.

Thailand MovNat Retreat attendees team lift a log as Master Instructor Vic Verdier (right) looks on Today

Others, like New York’s Ret Taylor, have created their own MovNat-inspired meetup.com groups that gather on weekends in Central Park to run barefoot through trails, swing their body from branches, hoist logs over their heads and generally act like, well, cave men and women.

Brandon Sewall, director of training at Primitive Movement, says it’s about value rather than vanity.

“Physical education a hundred years ago was about developing physical competency for real life,” he says. “Now fitness is degraded to padded machines and artificial movements patterns that are all about building vanity. It’s all about building show muscles instead of ‘go’ muscles.”

Participants in Sewall’s program may carry a large boulder down the beach or throw and catching cobblestones. Sometimes they walk and balance on unstable surfaces or sprint across a park or hang from a tree branch for as long as possible before landing.

“Primitive movement encourages organic resistance,” says Sewall. “You’re coping with the elements that Mother Nature throws at you instead of adding more volume and reps to your workout. You adopt not only to your environment but to the weather outside.”

And you’re also training your body to respond to unexpected -- or even unsafe -- situations.

“It doesn’t matter if you can bench 300 pounds if you can’t run upstairs and carry someone down who’s unconscious before a burning building is about to collapse on you,” he says. “It’s about being strong but also helpful and useful.”

Mishka Shubaly, a 36-year-old writer from Brooklyn, likes the functional aspects of the paleo workout.

“If you want to … be able to lift things or run fast or run a long time -- then doing exercises that incorporate the full range of motion, complex exercises that involve your entire body, that’s going to be the stuff that’s less likely to get you injured,” he says. “And more likely to get you to a level of actual fitness as opposed to just being a show pony.”

With the paleo workout your mind and your body don’t get bored, so you avoid fitness plateaus or peaks.

“With this method of training, it’s a never ending 45-degree angle,” says Sewall. “You get better and better and better at each of these skills.”

MovNat Workshop participants in Orlando, Fla. practice a foot-pinch climb using a lamp post Today

Exercise physiologist and personal trainer Jason Karp has a few reservations about functional training, despite its popularity.

“I totally agree with getting away from isolated movements in the gym with machines and doing more functional movement but I don’t know if we should be telling people to climb trees,” he says. “That’s taking it to the extreme.”

Instead of leaping from the gym into the branches of a Japanese maple, he suggests taking things slow.

“Transition away from the machines that guide the movement and use more free weights that are three-dimensional movement,” he says. “And then use your own body weight. Do body weight exercises like chin-ups and pull-ups and pushups rather than lifting external weights off the ground. Do things that are similar to what you do in real life, like squats, which is like bending down to pick up a pile of laundry.”

Sound advice since no matter what your fitness level, that cave will always need cleaning.

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