All Jared Shamburger wanted was to get stronger.

The 17-year-old’s father and brother had been bodybuilding for years, and Shamburger felt he had to “catch up to them and get as big as them,” he told ABC13.

To that end, he spent 90 minutes last month lifting weights at his Houston area gym. When he got home, he was sore—extremely sore. “Everything hurt,” he said. “It hurt to the touch. It was swollen.”

When the pain hadn’t subsided a few hours later, his mother, Judy Shamburger, grew concerned. “The mama bear in me kind of took over,” she said, “and I called the pediatrician and said, ‘I really think my son has rhabdo.’”

Shamburger’s mother was referencing rhabdomyolysis, an obscure muscle disorder that has become increasingly common in recent years. But rhabdomyolysis—or rhabdo for short—didn’t use to be a condition that impacted low-level lifters; it attacked elite athletes: ultramarathoners, CrossFitters, Division I sports teams. And it’s become increasingly common as everyday gymgoers are pushing through intense workouts.

Unlike Jared Shamburger, Alexis Feszko knew exactly what rhabdo was when she got it. For Feszko, a certified personal trainer based in Pennsylvania, all it took was a routine of bicep and tricep exercises that she described as not “too heavy at all.” But still, she told The Daily Beast, “Within 24 hours, I was in agonizing pain… my biceps and triceps had swollen astronomically, like tripled, quadrupled in size. It felt like my bones were going to break and my muscles were going to explode.”   

The biology behind Feszko and Shamburger’s pain—and rhabdo itself—is relatively simple. When an athlete works beyond their limits, their muscle fibers die, David Geier, an orthopedist and sports medicine specialist based in Charleston, South Carolina, told The Daily Beast. “The breakdown products of muscle get into the bloodstream. And little amounts of that would be OK. But a lot, that’s when you get organ damage—and it’s usually kidney damage.”

What Geier describes isn’t the only form of rhabdo. Tragic accidents—like car crashes, or falling from a high level—can cause the same type of muscle death, and the same consequences. The subset afflicting Shamburger and Fezsko is known as exertional rhabdo, or rhabdo that’s caused by exercise.

Like Shamburger and Feszko, most exertional rhabdo patients suffer from extreme muscle soreness and swelling, as well as muscle weakness and dark red or brown urine. Treatment is simple—an IV drip and pain medication—and often extremely effective. Most patients return to full health after brief stays in the hospital (although Feszko says she contracted rhabdo four more times, without exercising). But if left untreated, components of the muscle fibers cause tubular kidney cells to die, which eventually leads to kidney failure. This could mean dialysis, or, if left untreated for even longer, death.  

A second risk of untreated rhabdo is compartment syndrome, which occurs when the injured muscles swell so severely that the surrounding fascia tighten and cut off blood supply. Without surgery to release the pressure and resume normal blood flow, the muscle tissue can die.

“If he hadn’t caught it, if he hadn’t told me, if we had just gone out of town about our way…” Judy Shamburger told ABC13, “I can’t even imagine. And I don’t want to, about what could have happened.”  

For much of the condition's history, the Jared Shamburgers of the world didn’t have to worry much about rhabdo. It was an injury that hit high-intensity athletes, like the 22 high school football players who got it in 2010, the 13 Iowa State football players who got it in 2011, or the six Ohio State lacrosse players who got it in 2012, all after grueling mandatory workout regimens.

But with the recent rise in high-intensity enterprises like CrossFit and SoulCycle—and the cultural ethos that everyone should look like a bodybuilder—it’s now becoming a much more common problem.

In 2017, the academic research manager of the Princess Alexandra Hospital in Queensland, Australia, published an explainer on the relationship between rhabdo and high-intensity exercise. In reviewing the cases that presented in his hospital, he discovered that between 2012 and 2017, there had been a “20-fold increase in cases compared to the previous five years.” Between 2010 and 2014, there were 29 rhabdo cases at NewYork-Presbyterian alone.

“It felt like my bones were going to break and my muscles were going to explode.”
— Alexis Feszko

These discoveries, as well as a series of higher-profile cases, have led many to blame the high-intensity fitness classes that have exploded onto the fitness scene in recent years. Last year, The New York Times published an article linking rhabdo to spin classes, especially for first-time attendees. Eric Roberston, director of Kaiser Permanente Northern California Graduate Physical Therapy Education, published a lengthy article in which he linked rhabdo with CrossFit. In the article, entitled “CrossFit’s Dirty Little Secret,” he relayed the story of a colleague who contracted rhabdo after a regular CrossFit workout, attributing her experience to the “elitist, push yourself to the limit culture of the discipline,” and derided the sport for designing a grotesque clown cartoon called “Uncle Rhabdo.”  

But Joe Cannon, an exercise scientist, personal trainer, and author of Rhabdo: The Scary Side Effect of Exercise You’ve Never Heard Of—one of the only books about rhabdo and exercise on the market—thinks the problem is much bigger than the dogma of any individual gym or fitness routine. The real problem, Cannon argues, is an overwhelming lack of education that spans gyms, personal trainers, and the general public.

“Most fitness organizations do not cover rhabdo in their textbooks,” he told The Daily Beast, although he notes on his website that CrossFit is actually one of the few organizations that does cover rhabdo in their trainer’s manual (PDF), devoting at least nine of 117 pages to the topic.

“I teach personal trainers. I’ve worked with thousands of them over the years,” Cannon added. “I can tell you that most of them have never heard of rhabdo.”

He also notes that 30-minute workouts, often the norm in first-time personal training sessions, put pressure on trainers to work their clients too hard, too quickly. “They’re squeezing a lot of intensity in a short time period,” he said. “And that’s really the thing with rhabdo. It’s when you do a lot of stuff you’re not used to doing.”

Geier agrees that too hard, too quickly is a recipe for disaster—especially in the case of athletic coaches who aren’t aware of rhabdo’s danger. “In my world, sports medicine, where we hear about it is these kids coming back from a vacation or summer break, they’ve had time off, and then the team decides to do these really really hard workouts, and you just can’t do that. You need to work people back into that kind of exercise, slowly.”

But Cannon also blames reality TV shows, which he says provide the public with an unrealistic expectation of how they should exercise. “I throw all the TV reality shows under the bus,” he said. “You look at Biggest Loser, you look at Extreme Weight Loss, and whatever else, you normally see personal trainers beating the daylights out of people. And that says to the population, ‘Well that’s what I’ve gotta do to lose weight.’”

This expectation only gets worse, he adds, when mixed with the pervading “no pain, no gain” mentality of fitness. “The population in general thinks, ‘If I don’t feel sore, then I didn’t have a good workout,’” he said. “And that’s a myth. I tell people this on purpose in every class I teach: You don’t have to feel sore to reap the benefits of exercise.”

Instead, Cannon encourages his clients—and anyone seeking to avoid rhabdo—to start slow, and pursue full-body circuit training with light weights and minimal reps.

Geier recommends a similar level of caution.

“While you’re working out, if you’re worried something’s going on, you look for more than just normal muscle soreness,” he said. “Like, ‘My muscles are really hurting, they’re starting to swell.’ You don’t try to push through that. You stop working out. If it goes away, great, then come back another day. If it’s not getting better pretty quickly, go to an emergency room.”

This plan might not promise the same results as a high-weight, high-rep, high-intensity workout. But as more people are starting to learn, it’s far better to go slow than to get rhabdo.

Read more: