Avid runners are known for their fanaticism. Trail runners ratchet that up a notch.

It’s not enough for them to push their heart and lungs until they get that runners’ high. They want to enjoy the scenery, too.

“I refer to Harbison State Forest as ‘God’s Gym.’ (Not to be confused with Gold’s Gym!),” said trail runner Les Tilyou via e-mail. “All of God’s creations are in the woods: the dirt, the trees, the rivers, the animals. What better place to be?”

Several dozen regulars run the nearly 30 miles of trails at Harbison nearly every afternoon, and another large contingent hits the paths on weekends. They will be joined by many of the best road runners in the area on Saturday for the only trail race in the year-long Tour de Columbia series.

It’s part of the annual Friends of Harbison State Forest event, which celebrates the recreation mecca. The majority of the forest’s visitors are mountain bikers, but the trails also get a lot of use from hikers, dog-walkers and trail runners, said forest manager Russell Hubright.

Trail running isn’t for everybody. Brittle ankles can be tested by roots. You can’t just put your mind on autopilot on a trail. And you might hit a spider web.

But you won’t be hit by a car.

That’s No. 1 in Tilyou’s list of the advantages of trail running over road running. Among the other entries: less boring, easier on the joints, a more diverse workout and cooler than pavement. But Tilyou keeps coming back to the natural advantage.

“I’m able to get to some great locations that are only reachable on foot,” he said. That includes the bluffs at Harbison overlooking the Broad River.

Eric Robey likes to run at Harbison with his dog, Scout. “He’s my four-legged training partner,” Robey said of his husky-lab mix. “Man, he loves to run. You look at him and say he could pull a sled.”

Robey races through Harbison four to six times each week. Robey likes that he can change his routine simply by taking a different trail loop. He and Tilyou said the runners co-exist well with the hikers and bikers at Harbison. Even when the parking lot is full, the trails don’t seem crowded.

Harbison is by far the most popular local trail-running location. The sandy base for the trails at Sesquicentennial State Park create a special challenge, as do the often moist trails at Congaree National Park.

Also, the trails at those parks are mainly flat. Avid trail runners live for hills. Going uphill works on the calves, hamstrings and buttocks; going downhill puts extra stress on the quadriceps. But unlike road running, when the inclines are usually long and slight, many of the hills at Harbison are quick and steep.

Trail runners who really want to push their body head for the mountains. The various trails leading to the Chattooga River in Sumter National Forest are popular with gluttons who like long, twisty decents followed by long, twisty ascents.

Road runners might need to switch shoes when they hit the trails. Ideally, they should wear extra-stable shoes for running up and down hills studded with roots and rocks, according to Brett Baker at Extra Mile Running Store in Columbia.

If you’re going to run trails just a couple of times, you can stick with your regular running shoes. But frequent trail runners should get shoes designed with a post in the instep to help prevent twisted ankles, Baker said.

Baker doesn’t just sell the shoes; he uses them as a frequent runner at Harbison.

“I love being in the woods,” Baker said. “I love that you don’t have to worry about traffic. And running on a trail, you can’t see that far in front of you, so you don’t think about how much farther you have to go.”

Reach Holleman at (803) 771-8366 or jholleman@thestate.com.

IF YOU GO

The Friends of Harbison Forest’s Earth Day celebration is this weekend at Harbison State Forest at 5600 Broad River Road.

Saturday

9 a.m.-noon: Four-mile trail run, call (803) 788-6992

9 a.m.: Nature walk with Rudy Mancke

11 a.m.: Backyard wildlife habitat workshop

1 p.m.: Beekeeping workshop

3:30 p.m.: Nature walk with Native Plant Society

Sunday

10 a.m.-3 p.m.: Race to the River mountain bike event, call (803) 788-6992

2 p.m.: Broad River canoe trip, call (803) 796-4505

4 p.m.: Broad River canoe trip, call (803) 771-0353

NOTE: Parking fees will be waived at event locations in the park.