SAN JOSE — When Miguel Vivaldo arrived at Sunrise Middle School on Monday morning, it was in a wheelchair. Miguel, 13, told friends and teachers that he had fallen in the shower because he was so tired after completing a 100-mile ultra-marathon over the weekend.

But just when he had persuaded everyone that he was hurt, the mischievous eighth-grader stood up to show that he was just fine after completing the mind-boggling distance in 23 hours, 48 minutes, 21 seconds at the Run-de-Vous in San Martin.

That makes Miguel quite possibly the youngest person ever to finish a 100-mile event in less than 24 hours. And perhaps even more remarkable, Run-de-Vous race director Rajeev Patel said Miguel covered the last two miles in just 18 minutes.

But Monday, Miguel sounded almost as proud of his successful prank.

“I fooled most of my friends and even Teresa, too,” Miguel said of Sunrise director Teresa Robinson.

He got me, admitted Robinson.

“I really felt terrible when he rolled into school,” Robinson said. “But then he finally smiled.”

Miguel already had plenty to smile about after he placed 11th among 30 finishers. Fifty-nine runners had started the ultra-marathon.

“He just executed his strategy perfectly,” said Kermit Cuff, who coaches Miguel. “He didn’t make any mistakes. I don’t know how he does this. It’s like he has been doing this for years and years.”

Actually, Miguel has been running for less than a year. But he quickly boosted his mileage to marathon distances — and beyond. They chose the Run-de-Vous to attempt a 100-miler because it was held on a flat, two-mile loop that allowed friends and family to take turns running with Miguel.

For the first 88 miles, he would run a mile-and-a-half and then walk the other half-mile of each loop. He took only a single, 10-minute break, where he caught a quick cat nap. But Miguel ran the final 12 miles when he realized that he could break 24 hours.

“He just took off at that point,” Cuff said. “I just don’t know how anyone his age can run like that.”

The result, Patel wrote in an email, is that “to the best of my knowledge,” Miguel had become the youngest runner to finish a 100-mile race in less than 24 hours.

“I didn’t think I was going to finish as quickly as I did,” Miguel added. “But I started putting more effort into it at the end. I was tired and sore. But it was fun.”

Cuff said he knows of only one other boy close to Miguel’s age who has finished a 100-mile race. Earlier this year, 12-year-old Colby Wentlandt completed a difficult trail course near Las Vegas’ Red Rock Canyon Natural Conservation Area with a time of 32 hours, 7 minutes, 30 seconds.

But there is something much more difficult than running for Miguel. Robinson had him speak to the school about his accomplishment.

“I’m pretty shy,” he said. “But I told them that if you decide to do something, you should never give up on that goal.”

Contact Mark Emmons at 408-920-5745. Follow him at Twitter.com/markedwinemmons.