Sean Gobin calls it a death spiral. Soldiers go back and forth between domestic normalcy and the ugliness of war, then retire. Traumatic memories play in a loop. Cynicism festers. Vets pull away from family and friends. The anguish, regardless of whether it's diagnosed as post-traumatic stress disorder, becomes internalized. Some self-medicate with alcohol or drugs.

As a 2nd Lieutenant in the U.S. Marines, Mr. Gobin fought his way into Baghdad in a tank in March, 2003, played Russian roulette with IED-planting insurgents in Fallujah for seven months, and spent a year training security forces in Afghanistan.

When he donned civilian clothes for good in 2012, he enrolled in grad school. Classes didn't start for five months, so he and another ex-Marine hiked the legendary Appalachian Trail from Georgia to Maine, stopping at VFW (Veterans of Foreign Wars) posts in towns along the route to collect pledges for disabled soldiers.

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Their $50,000 fundraiser caught the eye of the not-for-profit that operates the 3,500-kilometre trail. The very first person to thru-hike the route, Second World War vet Earl Shaffer, did it over five months in 1948 to escape the sights and sounds of battle. The Appalachian Trail Conservancy wanted to do something to honour Shaffer, who died in 2002, and gave Mr. Gobin a call.

Last summer, 14 former soldiers set out on foot from the trailhead in Springer Mountain, Ga., supported by Warrior Hike. Scientists are only starting to understand the links between physical activities, such as walking, and mental health. Clinical studies have concluded that exercise could help wean people off antidepressants, and laboratory evidence shows that stress levels drop when we spend time in nature. But Mr. Gobin has unique insight into how walking in the wilderness can help soldiers.

How did completing the Appalachian Trail affect you?

War drains your faith in humanity. You come home, disassociate and disconnect, and live in a world of grey. Hiking all day, you've got time to process your thoughts. You relive your combat experiences 100 times each day. But out in nature for so long, you have a chance to think about what's important, about what you want to do next. Toward the end of the trail, I realized how beautiful the country is. The colour came back to my life.

What did it do for the vets who hiked last summer?

Physically, it's common to get out of the military and gain a lot of weight. You're not being forced to run, so you let yourself go, and that adds to your depression. But if you do a 16-mile hike every day for six months, which is more gruelling than anything you do in the military, you'll be in better shape than you've been in your entire life.

A long-distance hike also reveals character. People have bad days. You're dealing with your own struggles, the weather, the terrain. How you cope with that and interact with other people facilitates personal development. If you're in a group, you try to help others when they're down. That helps you regain a sense of camaraderie, that feeling of being on a mission, which gives you a sense of purpose again.

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Were there any problems?

Some guys made poor decisions and very quickly learned from them. In the beginning, they were drinking and partying and falling behind. And they asked, "What am I getting out of this? Maybe drinking isn't important. Maybe doing something bigger than myself is more important."

Was there much interaction with other people outside the group?

You get to meet all the thru-hikers, and most are vastly different than the type of people you're used to interacting with in the military. You're exposed to this whole other side of society, which is an important part of the socialization process for people who might hole up when they come home.

Then there's the outpouring of support in all the small communities the trail goes through. You walk into a town when you're with Warrior Hike and there are people lined up to shake your hand and say "thanks," people who want to give you rides and meals.

Meeting with other veterans is amazing, too. Guys who fought in Vietnam 40 years ago, they say, "I know what you're going through. There's a light at the end of the tunnel."

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What's happening in 2014?

Warrior Hike has partnered with Georgia Southern University. Psychology department researchers will be publishing a paper on the benefits of long-distance hiking for veterans with PTSD and providing tele-therapy counselling to help vets recognize triggers and learn coping techniques.

In addition to the Appalachian Trail, we're sending groups onto the Pacific Crest Trail and Continental Divide Trail next year. But seriously injured soldiers can't hike, so we're looking at adding a cross-country bicycle trip and a paddling expedition down the Mississippi. I've also been talking to a DEA agent – first-responders experience a lot of PTSD – and someone who runs a shelter for women who have been victims of violence. There's a whole other segment of society that could benefit from this. It's bigger than just veterans. And Warrior Hike can be replicated in other countries, too.

This interview has been edited and condensed.