A typical dad and son, except for when they’re … NINJAS!

AYER — Even Superman had his kryptonite.

Robert Logan and his son Robert Jr. — extreme fitness buffs who train for absurdly tough and intricate obstacle courses in their spare time — found they shared the same weakness. But unlike most other athletes, they discovered the limits of their strength and skill on national television late last month, in front of hundreds of thousands, on the reality competition show American Ninja Warrior.

Logan Sr. is still paying the price for an injury he suffered on set months ago in Miami. Even though he ruptured his Achilles tendon and needed surgery, he captured the hearts of viewers when he demanded that paramedics wheel him in a stretcher down the course so he could watch his 23-year-old son run the modernized gauntlet right after him.

The Logans have been training for years for the popular program. They built an obstacle course in their backyard, tailored to the show’s specifications, which overlooks Grove Pond in their small Ayer neighborhood.

This week, Logan Jr., a Web developer, effortlessly leapt off a ledge onto a bouncing trampoline before landing between two wooden boards set about 5 feet apart in his yard. In the training exercise, known as “the jumping spider,” he used his muscles to hold himself up between the walls that his father constructed.

“Good work. Nice,” Logan Sr. said as they bumped fists.

Forty-five-year-old Robert Logan, known to show fanatics as “Ninja Dad,” is a project manager at BCM Controls, a security company. In a previous life, he worked as a stuntman for local independent films. He said about three years ago he was watching the show and wishing he had done something like it as a young man. Then he became determined to get on the show. He set out to lose weight, built his backyard obstacle course and pushed himself. That was about 2 1/2 years ago.

“I do it just to prove it to myself,” he explained. “Just knowing I could do most of it drove me to get back into shape so I could prove it.”

Logan Sr. went to Baltimore at the start of the Ninja Warrior season in 2013 but he went out on a tricky monkey-bar-style “circle cross” exercise in the preliminary round. He came home motivated to get back to the course, and built a similar challenge right under his deck. Now, Logan said he can do that cross motion back and forth three times without stopping. His constant training inspired his son to go for it, too.

“Just seeing him do it made me want to get to do it,” Logan Jr. said, “and we just love it. We love the training. We love the community it’s created, and we just love being able to do these insane obstacles. It’s a lot of fun.”

To the pair’s disappointment, there was no circle cross this time around at the Miami qualifying course. Instead, the two were required to leap from ledges onto fabric curtains, lunge onto cargo nets from 10 feet away and push themselves up floating ladders, all without falling into water.

The final obstacle of the day was a “warped wall,” a 15-foot curved ramp at practically a 90-degree angle to the ground. Aspiring “ninjas” must run up the ramp, grab onto the top and hoist themselves over to move on to the next round.

When Logan Sr. attempted the run up the wall, there was an audible popping sound in his leg. He slinked to the floor. The crowd gasped.

Reflecting back on the Achilles rupture this past week, the father said it was not nearly as painful as one would imagine. His adrenaline was racing; he said that’s how he managed to hold off being rushed to the emergency room.

“I wanted to be there for him. They wanted to take me right away and I said, ‘No, I need to see my son’s run,’ ” he said. “They brought me to the jumbotron and I said, ‘I need to get over there.’ … The medics were hesitant and I told them, ‘Listen, this is going to make good TV.’ ”

Logan Jr. made it to the wall just like his father. Under his dad’s watchful eye, the young man made it to the top of the ramp on a final try, but his grip slipped.

The men went home, defeated, but still pumped to try the wall out again for next year’s season. They traveled to Florida for the tryouts with a friend from Westford, Michael Oakes, who runs the Together Fitness gym in Concord. Oakes, 37, is now working with the Ayer family to train them for 2015’s Ninja Warrior show. Oakes’ neighbor is also allowing them to use his backyard to house a replica warped wall for practice.

When the Logans headed back to Massachusetts in April, having just camped out for five days to make it on the show, they weren’t even sure if they made the final edit for airing. The men said they were thrilled to see both their obstacles broadcast across the country in late June. Now they’re determined to get on the next season together, provided Logan Sr.’s leg heals in time.

“You almost go into automatic pilot mode when you do it,” he said. “I can’t tell you how I got from the first obstacle to the second, but I kept telling myself, over and over again, to go slow, and get your balance. That made the difference for me.”

To watch clips of the American Ninja Warrior show featuring the Logans, go to http://t.co/0SS2y8hmY8 for Robert Logan Sr.’s run, and http://t.co/56Va3GCn1H for Robert Logan Jr.’s.

Follow Samantha Allen on Twitter and Tout @SAllen_89.