A partcipant in the 2015 North Face Endurance Challenge. (Michael Hermsmeyer, Ultra Race Photos)

The slogan on the shirts provided by the North Face Endurance Challenge Series said it all: “Dirt, the original proving ground.”

Among the hills of the Potomac Heritage Trail and the rocks of Great Falls, what with the unexpected heat, uprooted trees splayed across the trail and the threat of snakes, this trail race truly was a test of endurance and strength.

I competed in the 50K race at Algonkian Regional Park in Northern Virginia on April 18. Officials said about 3,000 people participated in the different running categories in the area — from a 5K to the 50-miler over the weekend.

For me, this was only a training run for the Comrades ultramarathon, a road race in South Africa I’m planning to run at the end of May. This race — both my first ultra (any distance longer than 26.2 miles) and my first trail race — most definitely lived up to its billing. My running shoes, which weren’t meant for trail running, went from white to mud. My shins were bruised by flying rocks and debris, and my wrist was sore from catching myself from doing the dreaded face plant.

That’s what trail racers call comfortable.

Another partcipant in the 2015 North Face Endurance Challenge. ( Michael Hermsmeyer, Ultra Race Photos)

The Endurance Challenge Series, which started in 2007, is one of the larger trail race series, with six U.S. locations, plus one in Ontario. The series reflects a growing sense of runners’ wanting to ditch the roads and race on trails instead.

Trails, of course, are not a new thing: There are more than 60,000 miles of scenic, historical and recreational national trails across the United States, and outdoor enthusiasts hike, bike, walk and run them year-round. The solitude and the chance to connect to nature are big drivers for trail lovers.

As a competitive sport, trail racing is following the steady growth in popularity of running, yet it retains the intimacy and collaborative feel that trail runners love. The trails attract all kinds of runners, from speedy collegiate athletes to those who barely make the time cutoffs on road races.

“The background of the sport in the U.S. and around the world has always been incredibly accommodating toward people of all talents and physical abilities,” Bryon Powell said.

Powell, a D.C. lawyer who gave up his job to start Irunfar.com, a Web site dedicated to trail running, has been a trail runner for more than 20 years. Even though trail races have existed for decades — the JFK 50-miler, the first ultra trail race established in the United States, started in 1963 — Powell has seen an explosion in the popularity of trail running and races the past seven to eight years. In contrast to the major road marathons, trail races may have 100 racers or fewer.

Those smaller fields are due to distance, both in the length of the courses and the location of the races. Many of the ultramarathon races are on trails in more remote areas. Plus, the logistical challenges of trail racing can make it harder to have multiple aid stations like a typical road race.

Trail runners also tout the whole-body workout and the demand to be fully present in the moment. They treasure the ability to escape city life, to exchange the sounds of cars for the murmur of creeks and to have, as Doug Cassaro put it, “this primal feeling when I’m out on the trails, like I’ve become part of them.”

Cassaro, 29, an Arlington resident and coach with the DC Road Runners, who ran his second 50K Endurance Challenge race and fourth trail race overall at the event, prefers trails to roads and has taken on hefty trail challenges such as 100-mile races. (Something I won’t try. A MisFit has to have limits.)

Gaithersburg’s Catherine Rehm, 57, says, “The trails don’t punish the legs as much as asphalt and concrete and give you a whole-body workout — core training that doesn’t seem like core training.”

Rehm, who doesn’t describe herself as a competitive racer yet helps train hopeful marathoners with Fleet Feet Gaithersburg, ran the Endurance Challenge half-marathon with a cast on her left arm. She told me she prefers trails because they force runners to focus on their surroundings. They demand complete attention.

“Your mind, as well as your core, needs to stay engaged 100 percent of the time just to stay vertical,” Rehm said. “And that’s the difference between trail running and road running, as well as most forms of exercise — you need to focus on the moment you’re in.”

That concentration means the pace will be different. Cassaro told me that dealing with the different kinds of terrain and natural obstacles slows a runner down.

But that means more time to take in the beauty. As Powell told me, trails are a “magical transport to something that envelops and frees you personally.

“Trail running means so much to me that I choose those locations that inspire me on a daily basis. But you can find that inspiration anywhere. When I lived in Arlington, on weekends I would run over to Potomac Overlook Park. It wasn’t many miles, but I loved it. There’s these little pockets of escape inside the Beltway.”

Great running trails are plentiful in the D.C. area. For those who want to explore on their own, TrailLink, a Web site and smartphone app hosted by Rails-to-Trails Conservancy, covers every rail and multiuse trail in the country, and includes photographs and reviews. Also, the Trail Run Project highlights the technical difficulty of trails and has runner reviews as well.

Whether it’s a race or a quiet jaunt, look for a trail to take you out of the city and into nature. Take the time to connect.

As Cassaro said: “Life is about exploring. It’s about challenging yourself. Trail running helps me do both.”

Hitting the trails

Trail running can seem a bit daunting at first. Here are some tips.

Repetition, repetition, repetition: Successful trail running will require some changes to your running style. You’re running for feel, not pace, and you have to be diligent about knowing your surroundings. “Just like anything else, repetition is important,” running coach Doug Cassaro said. “Get out on the trails often so you can adjust to this style of running. The more comfortable you are on the trails, the stronger a trail runner you will be.”

Mete out your effort. The focus should be on having a consistent effort, not a consistent pace. The terrain can be unsteady and arduous, and trying to run at your road marathon pace will lead to problems. If you have to walk up the hill or run it at a much slower pace, then walk or go slower.

Be patient. Single-use trails may get crowded at times. Powell said to let other runners who are going slower know you’re there. Pass them only when you have sufficient room.

Don’t fight the obstacles. The obstacles are part of the fun, but they can be hazardous if you’re not mindful. On the more difficult sections, don’t try to keep an unrealistic and possibly dangerous pace. “The more relaxed you are, the easier it will seem and the safer you will be. If you fall, you’ll be more apt to injure yourself if you’re not going with the flow,” trail runner Bryon Powell said.

Do the research on aid stations. There won’t be as many stations in a trail race as in a typical road marathon, so know where they are and how many miles you have to travel before you start the race. And if you’re just out on a trail run, know where the bathrooms are, if they’re available on or near the trail.