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Crossfit is a fitness craze that has captured the world of fitness.

AJ Richards and his wife, Jessica, run Crossfit in Mesa, Arizona, and say members thrive on the burn because they know what they can achieve if they push themselves.

But amidst the hype and the build-up lies potential problems.

Sara Matthews, 26, is an avid runner. She has received several medals for marathons and was surprised when she learned she developed a rare condition after taking only one beginner Crossfit class.

"I couldn't eat, and I couldn't shower. I couldn't really move my arms at all," said Matthews.

Matthews continued to be sore, and she explained it as not a "normal sore."

"I started to tell myself, maybe it's just a really bad muscle soreness, and maybe it will go away after a few days, that sort of thing. The weekend came and it got more and more painful."

Rhabdomyolysis, or Rhab-do, can happen when a muscle group is traumatized, according to physical therapist Eric Robertson.

"Rhabdomyolysis has been something that we've seen before in extreme endurance athletes, ultra marathoners and sometimes in the military settings. What was surprising to me was that people were getting it after very brief Crossfit workouts," said Robertson.

If Rhab-do is not treated, it can be lethal. The tissues can break down, releasing a toxin that can overload the kidneys.

In some cases, Rhab-do can be cleared by flushing the toxins out.

"They told me they would just have to hospitalize me and pump me full of fluids," said Matthews.

Crossfit has responded to the growing concern by spreading awareness through a "vomiting clown mascot." However, Matthews does not find the humor in the mascot.

"Something that could possibly put you in the hospital and cause permanent damage is not something that we should be joking about with a cartoon character," said Matthews.

Crossfit instructor AJ said the mascot is just to incite discussion.

"In the crossfit environment, it's really competitive, but on a different level, because the types of exercising that they are doing and the weights they are lifting and the repetition on the joints and muscles is really damaging and can create overuse injuries," said fitness instructor Richelle Melde, about the Crossfit craze.

To prevent any injuries, AJ requires all beginners to take a "ramp-up" class to learn the proper way to lift. He instills the theory that only competition is internal.

Steve Heidman believes in the Crossfit workout after proving the doctors wrong when they said he would never walk again because of his four-story fall while rock climbing.

"What I've been able to achieve with Crossfit is nothing short of a miracle," said Heidman.

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