When Andy Petranek discovered CrossFit in 2004, it was love at first sight. The high-impact interval workout gave him the results he’d thought were lost to his younger days. And then there was CrossFit’s extreme, take-no-prisoners ethos, which appealed to Petranek as a former Marine. In short order, he went from doing the workouts to competing in CrossFit events and opening his own CrossFit gym.

In 2009, at the age of 42, Petranek qualified for the international CrossFit Games, the Olympics of the sport. Determined to perform well, he doubled down on his training, working out twice a day, upping his max dead lift to 375 pounds and doing 53 pull-ups at a time. The tough regimen took its toll – tennis elbow, golfer’s elbow, shoulder woes, knee pain, a persistent trick in his neck. When the event finally rolled around, all his aches and pains had combined into a deadening soreness. He finished a disappointing 62nd out of 74. The next year, his zealous training ended even uglier: with a ruptured hemorrhoid. The adrenaline, the intensity, the complexity – everything he loved about CrossFit – had conspired against him. “CrossFit had become my life’s obsession,” he says. “But it wasn’t making my life better.”

Petranek’s ultra-competitiveness may put him at the extreme end of the CrossFit spectrum, but his experience is hardly atypical. Since it was created in 2000, CrossFit has exploded into a fitness phenomenon, with more than 9,000 gyms worldwide. Devotees love the way CrossFit is designed to push their body to its limits, getting past the fatigue and monotony of traditional workouts. The downside? The full-on assault puts them at a very real risk of injury. “People have been bred to think of gyms as safe places to work out,” says Petranek, “but CrossFit flies in the face of that. It’s a sport, more like mountain biking or snowboarding.”

New research is putting numbers to anecdotal evidence of CrossFit’s risks. Yuri Feito, a professor of exercise science at Kennesaw State University in Georgia (and a CrossFitter himself), analyzed data from 737 CrossFit participants and found that 51 percent had experienced an injury in the year prior – from minor sprains to muscle tears to broken fingers. Of those, 10 to 15 percent warranted a trip to the hospital. Some injuries, he says, resulted from “overtraining – too many reps, not enough recovery.” Another study in the Journal of Strength and Conditioning Research calculated 3.1 injuries per 1,000 CrossFit sessions. That’s about the same rate as competitive weightlifting or training for a triathlon or marathon. Without proper coaching, CrossFit carries more risk than the typical gym routine, says Feito – particularly for former athletes now in their thirties and forties, whose bodies are not as durable as they once were. “The mentality of an athlete is there, but we forget we’re older,” he says.

CrossFit Inc., the company behind this fitness craze, points out that there have been fewer than a dozen personal-injury claims against its affiliates and argues that there’s no systematic risk to practicing CrossFit. Injuries could be “a product of something somebody did wrong,” says general council Dale Saran.

But the way CrossFit is structured, participants can easily get caught up in its competitive nature. Its popularity stems from the way it mixes traditional exercises (barbell lifts, gymnastic moves, push-ups) into a cocktail of maneuvers known as the Workout of the Day, or WOD. WODs can be as long as an hour or as little as five seconds – each day brings surprises – but they’re nearly always fast and grueling, and they’re usually scored. Athletes race to finish a set number of reps “for time” or perform as many rounds as possible of a combination of exercises. That scoring aspect, added with the fact that the whole gym often starts together when a buzzer sounds, creates a frenzy that can push athletes to sacrifice technique. If joints become misaligned during a barbell jerk, for example, tendons and muscles can be pulled “right off the bone, like pulled pork or pulled chicken,” says Steven T. Devor, an exercise physiology professor at Ohio State University who has studied high-impact interval-training regimens. It’s not uncommon for CrossFitters to finish a workout feeling flu-y or even by throwing up. (In fact, it’s something of a badge of pride: CrossFit’s unofficial mascot is a vomiting clown named Pukie.) A small handful of athletes have been diagnosed with a rare condition called rhabdomyolysis, in which muscle tissue breaks down to the point that it poisons the bloodstream.

CrossFit’s gyms aren’t necessarily equipped to ward off injuries, either. Unlike a wholly owned fitness chain or franchise, which follows set standards, CrossFit gyms operate autonomously. Owners license the brand, then choose their own equipment and create their own workouts. Their instructors need only complete a two-day seminar and pass a written exam. “You wouldn’t trust an electrician who has a two-day certification, would you?” says Andrew Galpin, an assistant professor of kinesiology at California State University, Fullerton. (He is quick to add that CrossFit is not alone, that few fitness certifications require much more than a written test.) “Some of the best trainers in the world are CrossFit trainers,” he says. “But there are some really terrible ones, too.”

Counters CrossFit’s Saran: “You have to accept a risk of injury as a reality of playing a sport, or just living a life. A 100-percent safe exercise has a zero percent chance of getting you fit. It’s you sitting on the couch with a helmet and kneepads on.” He argues that the risks of CrossFit are actually “significantly less” than those of other kinds of exercise. He cites a five-year program with the Jacksonville, Florida, police department that saw no injuries. In contrast, he points to an article in the journal Pediatrics reporting that older youth soccer players had an injury prevalence of 4 to 7.6 per 1,000 hours – higher than CrossFit’s.

Even so, it’s important to go into CrossFit with your eyes open, viewing it as a high-impact sport with inherent risks. Petranek, for his part, is still a practitioner, even after his CrossFit Games implosion, admitting he craves the challenge of “throwing myself against the wall, seeing what I’m made of.” But he’s also changed his mantra, from “Win at all costs” to “Live to fight another day.”

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