Congressman Aaron Schock, R-Ill., known for his youth and the rock-hard, washboard abs he flaunted on the cover of Men's Health, was recently flagged for using campaign funds to buy P90X fitness DVDs by a Washington Watchdog group, but his office has since dismissed the claim as a filing error.

The report from Citizens for Responsibility and Ethics in Washington (CREW) said the congressman's campaign committee reportedly used campaign funds to finance a stay at a  five-star hotel in Athens, Greece, buy workout tapes and reimburse his mother.

"Aaron Schock personally paid American Express directly for the [P90X] charge," Steve Dutton, Schock's communications director, told ABC News. "It was mistakenly reported on our FEC report filed [and] we corrected that mistake when it happened. The campaign never paid for the P90X DVD." Shock, first elected to Congress in 2008 at age 27, mistakenly reported to the FEC $319 in payments to exercise DVD maker P90X to his campaign, listing the expense as "health care."

But just what is the P90X workout routine that has taken the House by storm?

In 2011 Schock posed for the June cover of Men's Health magazine, revealing the congressman's well cared-for muscles and six-pack abs. The 30-year-old details in the magazine his workout routine - before a 5-mile run around the nation's capital, Shock clocks in at the weight room in the House gym at 6:30 a.m. The article also revealed Shock's, along with "a dozen or so congressmen," affinity for sessions of P90X, the exercise video series created by Tony Horton.

The fitness routine boasts an impressive clientele, from Twilight's famous werewolf Taylor Lautner to at least 25 members of Congress.

"The word of mouth factor has been incredibly strong since for P90X," Jon Congdon, the president and co-founder of P90X parent company Beachbody, told ABC News. Congdon credits the program's growth to its fast and effective results, which then leads customers to spread the word about the fitness program.

Credited as the man who sparked the fitness fad on the hill, former trainer Rep. Paul Ryan, R-Wis., is a frequent proponent of the P90X workout, which he says helps him maintain his body fat between6 and 8 percent.  Ryan told Politico in 2010 that he leads a P90X fitness class in the House gym every morning along with former Rep. Bart Stupak, D-Mich. and Rep. Kevin McCarthy, R-Calif., which P90X creator Horton frequents every few months.

"It works because it pushes your body in many different ways so that it gets out of its plateau," Ryan said, adding that the workout stresses the importance of muscle confusion. "And it works."

Congdon says members of Congress have retrofit the gym to serve the workout, adding pull-up bars and plasma TVs to the House gym.

Horton himself has singled out Ryan and Rep. Heath Schuler, D-N.C., as two of the biggest fans of the workout, which features a grueling routine of arms, abs, legs and cardio. He told the Washington Examiner last year that Washington's politicos hold their ground well compared with his Hollywood clients.

"Compared to most of my celebrity clients, I'm from Hollywood, there are a lot of divas and a lot of prima donnas, they want to be treated with kid gloves a lot of the time, but the congressmen work really hard, they are very impressive I have to say," Horton told the Examiner.

"It's funny, the rest of the country perceives that the [Democrat and Republican] congressmen can't stand each other, but then you see them working out and joking together," Congdon remarked. "It's a bi-partisan thing."