A culture that encourages participants to push themselves to their limits has earned CrossFit a reputation for extremism, says Eric Robertson, a physical therapist at Regis University in Denver. (ISTOCKPHOTO)

It seems as though nearly everyone who has heard of CrossFit has an opinion about it — even people who have never tried it. Aficionados claim that this brand of high-intensity workouts is a fast and fun way to get fit. Critics say that it’s a fast track to injury.

CrossFit workouts mix weightlifting exercises, gymnastics and cardio activities such as jump rope and rowing into short, intense combinations that change daily. A typical “workout of the day” (WOD) might consist of running 400 meters, then doing 21 kettlebell swings and 12 pull-ups before repeating this sequence two more times. One recent WOD gave participants 20 minutes to complete as many rounds as possible of 10 push-ups, 20 pull-ups and 30 lunges.

Besides the intensity factor, what distinguishes CrossFit from other gym-based workouts is its constantly changing exercises and emphasis on moves — bending and squatting, for example — that are functional in everyday life, says Russell Berger, a head trainer for CrossFit Inc. Rather than training people to become very good at a few exercises, CrossFit prompts them to do things that people do in real life, such as getting up and raising things off the ground, Berger says. “We’re just asking people to do them a little faster with a little more weight to help them get better at it,” he says.

The intensity of these workouts and a culture that encourages participants to push themselves to their limits has earned CrossFit a reputation for extremism, says Eric Robertson, a physical therapist at Regis University in Denver and founder of the blog PTThinkTank. “People tend to brag about the injuries that they got. They post pictures of their hands all torn up from lifting the weights, and it’s like a badge of honor.” Exercise-induced vomiting is so common among CrossFit participants that it even has a mascot — Pukie the Clown.

Not everyone sees the macho humor in this. It’s one thing to push yourself; it’s another to go beyond the point where your body is telling you to stop, Robertson says. He recounts the experience of a colleague — a young, fit physical therapist — who developed severe swelling in her arms and exertional rhabdomyolysis, a potentially life-threatening condition, after pushing herself through hundreds of repetitions of push-ups and overhead presses during a CrossFit class.

Strength training normally increases muscle power by creating microscopic damage to the muscle fibers, which the body then repairs, making them stronger. But if the damage is especially great, it can flood the bloodstream with myoglobin, a large protein that can quickly overwhelm the kidneys, leading to “rhabdo” and possibly kidney failure, Robertson says.

Unfortunately, Robertson says, the symptoms of rhabdo don’t turn up until the damage is already done. Prevention requires listening to your body. “Don’t exercise beyond exhaustion, and if you find yourself losing form, stop,” Robertson says. Avoid sudden and severe increases in repetitions.

While rhabdomyolysis induced by exercise is very rare, Robertson says, it’s common enough among CrossFit participants that it has sparked a nickname, “Uncle Rhabdo.”

Berger does not dispute that, when taken to an extreme, CrossFit has the potential to induce rhabdo. “CrossFit has been trying to educate people about rhabdo for the sake of prevention since 2005,” he says. “Use common sense.”

The question of whether CrossFit causes more injuries than other workouts is impossible to answer, because no rigorous studies of injury rates have been published, according to Robertson.

“Anecdotally, I haven’t seen people come into our clinic regularly who claim to have been injured by a personal trainer, but we do see many people in our clinic who claim to have been injured doing CrossFit,” Robertson says. Such damage includes back injuries from dead-lift exercises and overuse injuries such as tendinitis and rotator cuff damage, he says.

Such injuries aren’t inevitable, Robertson says, but it’s important to take the time to master proper technique. Many of the exercises used in CrossFit are unfamiliar to the typical gymgoer and require good form to avoid injury.

“The most common injuries we see from CrossFit are from use of poor form with the exercises,” says Claire Bowe, owner of the Rose Physical Therapy Group in Northwest Washington. Injuries occur, she says, when people overlook form in an effort to go harder and faster.

CrossFit’s relentless high intensity concerns Neal Henderson, an exercise physiologist, coach and owner of Apex Coaching in Boulder, Colo. Intermittent high-intensity exercise is a great way to get fit, Henderson says, but only when the body can recover. “Tolerating high intensity is different from adapting to it and benefiting from it,” he says. Studies suggest that constantly exercising at high intensity won’t lead to optimal results and may instead provoke overtraining — a drop in energy and performance that happens when the body isn’t able to fully recover from workouts.

Robertson advises people to start with individual training before beginning group classes. Look for an instructor who emphasizes form and safety.

“A big part of doing it correctly is not overdoing it,” says Steve Dumaine, a 40-year-old tuba player for the National Symphony Orchestra who works out at District CrossFit in Washington. He’s been doing CrossFit for about eight years, and he developed a neck injury a while back — for which he blames himself, not CrossFit. “I let my ego take control of my workouts, and I did too much.”

The injury didn’t lead him to quit, but it did change his goal from doing more exercises to doing them well, and he now takes more days off to give his body time to recover.

“It’s a way of fighting off getting older,” he says of CrossFit. “That’s why I do it — I want to be able to carry my bags of kitty litter into the house when I’m old.”