Walking through downtown Manhattan is nothing like tracking stone sheep in British Columbia, but Jason Hairston, an expedition hunter and former NFL lineman, has no problem loading up his pack with us to simulate a "training" session among city streets and skyscrapers.

Adaptation is one of his strengths. Back in high school and college, football was Hairston's life. He even got a shot at living out his dream with the Denver Broncos—until, at age 24, he was blindsided by an injury. "I broke my neck. Ended my career," he says.

And like many athletes taken out in their prime, he slipped into depression. "Football is so exciting. There’s so much adrenaline around it. When that’s gone, how do you get that again?"

As tough as it may have been at the start, eventually Hairston did "get it again." This time, though, it was through other passions: hunting, then the sport of business. "My connection back to the mountains was great to me," he says. "It was my medicine. It gave me another focus in life; something to look forward to and be excited about."

Hairston was born an outdoorsman. In his experience hunting and tracking, though, he had a hard time finding gear or products that met the needs and demands of expedition hunters. Seizing on that opportunity, he went into business with a partner and started Sitka—his first entry into the hunting gear space—before launching his own brand, KUIU, in 2012.

"We can produce the best line that’s ever been created because we can buy the materials that no one else can," he says.

And with the explosive growth of KUIU (something like $50 million in annual sales per year), plus an avid Instagram audience of over 100,000 followers, his company has taken off. "To test our product, I’ll travel through Japan, Vietnam, Italy—remote places. I’ve been all over the world."

But no matter where Hairston is, training for the next expedition doesn't stop—and rightfully so. On a hunt, expeditioners like Hairston can hike for 10 or more hours per day, at 2-4 mph, through some of the roughest terrain on earth.

According to Hairston, training for an expedition hunt has three key components:

  • Long, low-intensity walks and hikes with varying loads
  • Interval training/VO2 Max training
  • "Functional" strength movements

The long, low-intensity walks and hikes with loads are designed to replicate life in the mountains for 15 days. Due to his aggressive work-travel schedule, he's forced to train wherever he is. With the Men's Fitness team in New York, he found plenty of stairs to climb.

"This is a great way to train," he says. "If you’re traveling, you can always find stairs. It gives you the elevation, it gives you the movements you need." As for the load? Every single thing he needs and lives on for those 15 days is on his back. And if they're lucky, on the return trip, that weight might include the weight of an entire year’s worth of all-natural, hormone-free food.

Hairston adds interval training into his programming to improve his VO2 max, just like a distance runner. "I’ll do hill intervals either outside or on the treadmill," he says. The treadmill is tough, because it doesn’t slow down when you get tired. So it really can test your VO2 max. I’ll do those one day a week, or two days a week closer to the season. That really will help your aerobic threshold," he says.

He uses "functional" training to prepare his body for the twisting, turning, carrying, reaching, and stretching involved in navigating some of the world's toughest (and most unpredictable) terrains. His plan includes lunges and step-ups with weights to challenge his core and balance. He also does cleans and snatches for total body strength and balance. "It all ties together," he says.

Aside from training, Hairston is methodical about his team's prep. “We always build a gear list," he says. "We weigh everything. We put it on a spreadsheet that tells us exactly what we’re going to weigh. My packs are typically around 12 lbs before food—which is 20 lbs—water, optics, tripod, fire arm, and bullets," he explains.

And despite the incredible physical condition required to successfully complete an expedition (not to mention the expense), they’re more popular than ever, Hairston says. "It’s $50,000 now for some of these hunts, and people are willing to pay it," he says. Even people like Donald Trump Jr. (along with a Secret Service retinue) will embark on a challenge. "These guys have done some hunting, but to get them to understand what they are about to do and to respect it, that’s the hardest part," he says. "A hunter will, but getting these guys to do it as well…it’s going to be interesting."

Hairston sums up the expedition like this: "You’ll find new levels of suffering, and new levels of exhaustion, you never knew were humanly possible. That is pretty awesome, when it’s done. It’s pretty amazing."