Lowe Johnston, center, with John Hester, left, and his nephew Grant, right, after the Tough Mudder obstacle race earlier this month.

Think your adventure racing days are behind you? Maybe not.

Meet Lowe Johnston of Austin.

Johnston, age 74, competed in and finished his very first Tough Mudder race on May 2. Not only is he well above the average age of 29 for competitors in the event, a 10.2-mile course with obstacles scattered along the way, he’s got Parkinson’s Disease.

“It’s a great test of general physical condition,” Johnston says. “You need balanced overall strength.”

Johnston was diagnosed with Parkinson’s, a progressive disease of the nervous system, in 2001, just after his wife died. He takes medication to control his symptoms, which include tremors and problems with fine motor control. He says his symptoms didn’t bother him much during the race.

“I’ve been very very lucky. I’m doing really well,” he says.

Johnston is among the oldest participants to do the race, according to Jodi Kovacs of Tough Mudder. An 82-year-old competed a few years ago, and a 71-year-old recently raced in England.

Obstacles include crossing muddy pits, scaling walls, climbing ropes and leaping over fire. The hardest for Johnston? Something called Everest, a metal slide about 20 feet tall.

“It’s at the end of race and I was tired and cramping. You run up the slide and people at the top grab you and help you over. It took me about 10 times to get up that,” he says.

It took him about 4 hours to finish the Tough Mudder, including wait time at some of the obstacles. He says he walked away from the race with no ill effects other than a few scratches on his knees. He’s planning to do it again next year, and will prepare specifically for the race.

“I want to strengthen my hands to grip bars and vertical ropes, and will hang a rope back of my house to train pulling myself up using only my arms,” he says.

Johnston says he stays in shape by running and exercising. He completed the Mardi Gras Marathon in New Orleans in 2010 and the Cap10K this year. “You’ve got to eat right, exercise and get sleep,” he says. “I hope to use the Tough Mudder as an indicator that I’m still doing OK health-wise.”

About 1.3 million people have participated in a Tough Mudder race. Seventy percent of competitors are male, according to the race website.