Breaking the world record for the number of pull-ups completed in six, 12 and 24 hours was tough, Elmhurst gym owner Nick Janowitz says.

But it's not the toughest thing he's ever done.

That came 17 years ago, when he was a 20-year-old sailor and ran a marathon in less than four hours -- without training -- after being discharged from a two-week hospital stay for kidney failure.

Janowitz, of Downers Grove, also has walked for 24 hours straight, run ultramarathons and competed on the all-Navy wrestling team. He often works out eight hours a day as he leads classes in boxing, jiu jitsu or soccer at Patriot Sports and Fitness.

"I've always been doing difficult physical challenges like this," he says.

But let's get back to his latest feat, which he says is "in the top five" among most challenging things he's done: All those pull-ups.

Janowitz completed 3,650 in six hours, enough to break the world record of 3,515.

In 12 hours, he completed 5,907 to top the record of 5,742.

And in 18 hours, he did 7,621 pullups, breaking the 24-hour record of 7,600 -- and finishing six hours sooner.

He's working to send in all of the necessary video (from four cameras), witness statements (from two spectators and a police officer) and documentation (probably 50 pages worth), to earn certification of his record-holder status from Guinness World Records.

"I believe it just makes me tougher as a human being," Janowitz says.

This was the 5-foot-10-inch tall, 175-pound Janowitz's second attempt at breaking the 24-hour pull-up record, and it came on Oct. 27, his 37th birthday.

While completing the pull-ups, he and his supporters raised about $5,000 for a Naperville nonprofit called Pull-Up Bars for Patriots, which installs pull-up bars as memorials to fallen service members to remember their sacrifice and encourage physical fitness.

Janowitz's first pull-up record attempt was in April, outside at Elmhurst City Centre. He said the temperature dropped into the 30s overnight, making his body work harder to preserve heat and not as hard pulling his chin above a metal bar. His pace slowed and the record attempt was a bust.

"As many times as I have succeeded in life," Janowitz says, "I have failed in life."

Since that marathon-on-a-whim 17 years ago, Janowitz has continued pushing his body to the physical -- and mental -- limits because he knows it will prepare him for whatever lies ahead. He never wants to turn into a couch potato who gives up; he wants to fight. Just like he fights when his arms feel like they can't do another pull.

That moment came 14 hours into his latest attempt.

"I've prepared myself to hear that voice, that self-doubt," he says. "Now I actually look forward to when that happens."

Every minute on the minute during the 18-hour session, Janowitz would hop up to the bar and do a number of pull-ups. He started with a dozen each minute for the first hour. Then 11 during the second hour, 10 the third hour, and so on until he was doing four each minute toward the end.

To protect his hands from instant calluses and blisters, he held yellow car sponges between his skin and the bar. He limited his water intake and took only two bathroom breaks. He fueled in between pull-up bursts with bananas, sushi, protein bars, trail mix and pineapple.

Janowitz's April record attempt came with fanfare -- an event that started with 1,000 people in attendance, a police escort, a major charity push. But this time, Janowitz kept it quieter. His wife, Tracey, and their kids, ages 7 and 4, were there, along with some of his longtime trainees.

"It's been really inspiring for our members," he says about his record attempts, which also include an unofficial success at breaking the record for most repetitions of an exercise called a "burpee" in 24 hours, completing 10,164. "It helps them with their goal-setting."

Goal-setting has motivated Tracey Janowitz, too, who on Friday opened her own business, an "athleisure" clothing line called Sweaty Swag, by launching a store at Yorktown Center in Lombard.

Meanwhile, her pull-up champion husband doesn't plan on lowering his goals anytime soon.

Janowitz says he wants to get back into mixed martial arts fighting, possibly audition for the "American Ninja Warrior" TV show and continue engaging in challenges that pit him against himself.

"There's no one else to blame," he says. "That's what I like about it."