A single bootcamp class in January 2025 left one woman hospitalised for a week with a condition she had never heard of: exertional rhabdomyolysis, a serious medical event in which extreme exercise causes muscle cells to break down and flood the bloodstream with toxins.
The Personal Experience
Having spent the day hunched over her laptop, anxious and craving an intense workout, she booked a class at a nearby gym. The five-star reviews were full of promises: “Militant style instructor, but very motivating,” read one. Another described it as the “hardest workout of my life; extremely rewarding.” The gym was no-frills — just a room with a mirror.
After a standard warm-up, the class performed four sets of lateral shuffle push-ups across the floor, interspersed with standing, weight-bearing exercises. She started cautiously, dropping to plank position and doing steady, shallow reps while focusing on her form. But as upbeat music boomed and others advanced beside her, caution fell away. When the instructor encouraged the class to lower all the way down, she obeyed even as her form suffered. Having rarely done more than a handful of push-ups at a time, she was exhausted by the final set, collapsing on every rep and barely prying her torso off the floor.
The rest of the class became a blur. Nauseated, she told the instructor she needed to pause and stepped outside to suck cold winter air into her lungs. She returned to sit on the sidelines until the dizziness receded, then slunk back to her spot for the core section and cooldown.
That night, she felt what she thought was typical post-workout muscle soreness — the ache that feels like proof of a successful workout. But the next day, lifting her arms to wash her face was exhausting. Searing pain kept her awake that night. Two days after the class, her arms were so stiff she could not raise them more than a few inches, even to brush her teeth.
A Google search of her symptoms — pain, weakness and a new one, dark urine — brought up something frightening: exertional rhabdomyolysis. One article warned that debilitating pain after a new, intense activity was a sign to visit the emergency room. She went to the ER, suspecting she was overreacting. Doctors used bloodwork to test for the condition, which is typically diagnosed when a patient has too much of a muscle enzyme called creatine kinase (CK) in their blood — at least 1,000 units per litre, or five times the normal range, though some recent guidelines suggest only higher amounts, as much as 10,000 units, warrant diagnosis and inpatient treatment.
Her CK count was so high the machine in the emergency room could not measure it. A nurse had to do a second blood draw and send it to a more precise lab. The result came back at 57,000. Her seven-day hospital stay began. Her mother and sister traded shifts, acting as her arms for the week — scrubbing her teeth, feeding her, washing her face.
What is Exertional Rhabdomyolysis?
Normally, during exercise, muscles tear a little and then rebuild. A small amount of CK may enter the blood as a result, which healthy kidneys can filter out. But excessive exercise can harm muscle cells so much that their contents — including CK and a protein called myoglobin — overload the system.
“When the cell membrane starts to break down, the chemicals within the muscle cells start to get released, which can cause damage to other organs around the body,” said Dr Barry Boden, an orthopaedic surgeon at The Orthopaedic Center in Maryland who specialises in sports medicine. “If there’s enough of those chemicals from the muscle that reach the kidney, it can cause damage to the kidney.”
The symptoms are muscle pain even at rest, weakness and dark urine, though few people experience all three. Treatment involves early and aggressive administration of IV fluids to help the kidneys filter the toxins. It is possible to manage a mild case with at-home oral hydration, but it is always important to consult a doctor because mild symptoms do not always mean low CK elevation, said Dr Petr Schlegel, a CrossFit trainer and professor at the department of physical education and sports at the University of Hradec Králové in the Czech Republic.
Exertional rhabdomyolysis is dangerous and fatal in very rare cases. Researchers estimate that 10% of patients develop acute kidney injury (AKI), and some suffer other serious complications.
Before her own experience, the woman had never heard of the condition. Despite the common misconception that only unfit people can get it, even elite athletes are susceptible. “Anybody can get it — anybody that’s pushed to an extreme, taking a big jump in their exercise level, or doing something they’re not used to doing,” said Boden. “Everybody has muscles, and if the muscles are damaged enough, you can develop rhabdomyolysis.”
People with certain conditions, such as sickle-cell trait and hypokalemia, are predisposed. Dehydration, exercising in high temperatures and humidity, and certain medications including statins and antipsychotics have also been linked to an increased risk. Some individuals may have a genetic or metabolic predisposition.
Boden authored a study estimating there were over 40,000 exertional rhabdomyolysis cases in US hospitals from 2000 to 2019. But he said it is impossible to get a precise count, as no organisation collects the data. This number is likely an underestimate, as the condition is probably under-reported, said Schlegel. Since the symptoms closely resemble those of delayed onset muscle soreness — the normal ache people expect after a workout — individuals may not seek care.
Data indicate exertional rhabdomyolysis is on the rise. In Norway, Australia and the US, researchers have observed an increase in hospital records between the 2000s and 2010s. This year, hospitals in a Canadian province reported a surge in cases. Researchers suspect the popularity of high-intensity workouts is behind the rise. They are efficient and produce measurable progress, but are risky if misused, said Schlegel: “Evidence suggests that high-intensity exercise, especially when combining strength and endurance elements, carries the greatest potential to induce [exertional rhabdomyolysis].”
The condition has been a significant concern in military training programs, leading to updated clinical practice guidelines for recognition, management and safe return-to-activity decisions. In the UK, there have been legal cases involving exertional rhabdomyolysis, with individuals seeking compensation after developing the condition due to gym accidents or negligence by trainers. In one known case, an individual received a £75,000 settlement after a trainer disregarded low hydration levels and proceeded with an intense induction session. While specific regulations for ER prevention in the UK fitness industry are not explicitly detailed, general health and safety regulations for gyms apply, including ensuring equipment is safe, staff are trained and clear safety warnings are provided.
Prevention and Self-Monitoring
Prevention guidance has been pretty consistent since the earliest studies from the 1960s: vary exercises to avoid overloading one muscle group, incorporate rest, and gradually build intensity when starting something new or after time off. Starting low is especially important when targeting large muscle groups such as biceps, triceps and quads.
“It’s that hyperintense going from zero to 100, really intense workouts of large muscle groups, that puts people at risk,” said Dr Bryant Walrod, a sports medicine physician and the head team physician for the Ohio State Buckeyes. Weight matters, but so do reps; an outrageous number of low-weight exercises or calisthenics — hundreds of push-ups or squats, for example — is the trigger in many cases. Walrod also advises doing a different kind of workout from one day to the next.
Eccentric exercises like push-ups — where muscles lengthen — are particularly likely to cause injury. In a 2024 article about how to prevent rhabdomyolysis in student athletes, the National Federation of State High School Associations called push-ups the “No 1 cause” of rhabdomyolysis. In April, Texas families filed a lawsuit against a charter school after 20 children were hospitalised after hundreds of push-ups.
Walrod said collegiate sports professionals became more vigilant about prevention after University of Iowa football players were hospitalised with exertional rhabdomyolysis in 2011. “That case spurred better control of workouts, better monitoring, and better input from the trainers and strength coaches.”
“Where we see most of the cases is that athletes are being pushed or threatened or punished [contrary to industry standards],” said Dr Rebecca Stearns, COO at the Korey Stringer Institute for preventing sudden death in sports. Coaches are not exercise physiologists, and even when well-intentioned may not have adequate training to prevent overexertion, said Boden.
Similarly, there is no guarantee fitness instructors understand the risk. “People may be going in unconditioned and doing too much too soon,” said Walrod of these classes. CrossFit incorporated prevention into its trainer curriculum after reports of severe cases among participants, but in general, class participants should self-monitor.
Unfortunately, sensing that something is wrong is a subjective measure; there is no universal metric. “I never have a very satisfying answer to that, but I do think it’s a line we need to be vigilant about always, and it changes from day to day,” said Dr Natalia Petrzela, author of Fit Nation: The Gains and Pains of America’s Exercise Obsession, a longtime fitness instructor and professor of history at The New School.
“You know your body the best, and if you feel like something isn’t right, it’s time to speak up,” said Walrod. Sports medicine physicians advise people to stop exercise immediately if unusual pain occurs; in the event of excessive muscle breakdown, it is critical to stop the movement right away.
Speaking up in a class setting can be difficult. Many feel self-conscious about pausing or modifying activity, especially if an instructor is singling them out. Petrzela said she motivates participants in her class but also expresses a key caveat: “Only you know what you can do today.” She said this language “helps [them] find that very important and difficult-to-discern line”, adding that this nuance might get lost in classes with less experienced instructors who give inflexible instructions.
After her discharge from the hospital with a firm instruction — no exercise except walking for a month — the woman had to learn what an appropriate challenge felt like, how to self-monitor and discern between safe discomfort and overexertion. During the fateful class, she had ignored the alarm bells, perhaps chasing endorphins or trying to prove she was not weak. Ironically, her arms atrophied to below baseline as a result. Over a year later, she is still building her strength back, but not at bootcamp. She now opts for low-impact methods such as barre and pilates where she can modify if needed, and there is no need to keep pace with others. Sometimes she tells instructors about her medical history so they understand what is happening if she pauses. Verbalising it also reminds her to be careful. Finally, she avoids anything new or especially difficult when she is having a hard day. Fitness culture taught her that pain is gain — but now she knows that is not always true.
