A rare condition killed a 24-year-old first-time NYC Marathon runner. Its warning signs can be easy to miss.

Just two miles short of the finish line of the 2026 New York City Marathon on Nov. 1, 24-year-old runner Rachel Apa collapsed. She died of a rare and potentially life-threatening illness that can be brought on by excessive exertion, the New York Times reported.

It's called rhabdomyolysis , and while there are relatively few cases nationwide each year, it can strike during endurance or intensive exercise, including marathons.

Apa was running her first marathon to raise money for Parkinson's disease in honor of her late grandfather, according to the New York Times. But Apa was no stranger to athletics, having played Division I field hockey in college. Her family said Apa had been in "perfect health." Plus, she'd been training for the race for months.

But at mile 18, Apa texted her father, Steve, who'd been checking in at each mile: "Ow." At the end of the next mile, she wrote, "Ow ow." She stopped responding after that. Apa's mother, Michelle, was at the race and had watched her daughter run by earlier on. Her parents noticed on the marathon tracking app that Apa stopped moving after mile 24.

Apa collapsed just after running past hospital social worker Michaela Nichols, who was cheering on participants. Nichols ran over and checked Apa's pulse, but couldn't find one. Three other people — two of whom said they were physicians — ran over to give Apa CPR. Marathon medical staff tried to revive her with a defibrillator before an ambulance arrived. She was taken to Mount Sinai Medical Center and treated for six hours, but could not be saved.

Her father told the New York Times that Apa's cause of death was rhabdomyolysis.

It's a dangerous medical condition that occurs when skeletal muscle (the kind that connects to bones and allows you to move) gets damaged and rapidly breaks down. "The internal components of muscle cells, which include various electrolytes, proteins and enzymes, spill out, and those in turn can be toxic to the kidneys and dangerous to the heart," Dr. David Mariuma , a nephrologist at Stony Brook Medicine who was not involved in Apa's treatment, tells Yahoo. Specifically, the released molecules can lead to kidney failure and life-threatening heart arrhythmias if not treated quickly and properly.

This destructive process can be triggered in several different ways. The most common cause is not exercise, but injury, according to the Cleveland Clinic. Traumatic crushing injuries are the most likely to induce rhabdomyolysis (often referred to as simply "rhabdo"), but severe burns or electrocution can also lead to muscle breakdown.

Cleveland Clinic reports that there are about 26,000 total cases of rhabdomyolysis in the U.S. each year. It's harder to say exactly how many are due to exercise, but one study estimates that physical exertion — including endurance athletic activities, manual labor and intense exercise — may account for up to 47% of cases. The true number is likely higher, Mariuma says.

Although it's uncommon, anyone can develop rhabdomyolysis, regardless of age and athletic experience.

Dr. Jessica Tomazic , a sports and exercise medicine staff physician with the Cleveland Clinic who was not involved in Apa's care nor familiar with her case, tells Yahoo that a combination of risk factors can increase the likelihood. They include:

Heat, or temperatures one is not accustomed to exercising in

Certain genetic conditions, including sickle cell disease

Drug use (particularly cocaine, according to Mariuma)

Prior heat illness, rhabdomyolysis or a family history of rhabdo

Rhabdomyolysis is also more common among men, people who smoke and those with obesity. In rare cases, certain medications, including statins, can lead to the condition when the dose is too high for an individual patient, says Mariuma.

Higher rates of rhabdomyolysis have also been linked to endurance athletes, spin classes and high-intensity interval training, including the P90X workout program. And researchers have looked specifically at cases of rhabdo among New York City marathon runners. An Icahn School of Medicine at Mount Sinai study identified at least one rhabdo incident each year between 2017 and 2024 (excluding 2020, when the marathon was canceled due to COVID). Twenty-one-year-old Austin Stallman died of rhabdomyolysis after collapsing during a 9-mile Navy SEAL training run in Texas earlier in 2026.

"This is the kind of thing where sometimes everything could go right, you could do everything you're supposed to do and it still happens," says Mariuma.

The condition can be hard to spot because many of its symptoms are similar to what some people experience during intense physical challenges. It typically begins with soreness or pain that feels more extreme than usual for the activity, according to Mariuma and Tomiazic. Pain is especially concerning if it's accompanied by more weakness than normal or "any sense of confusion, nausea, or what we call constitutional symptoms that are not specific to the muscle — a general sense that something is off, or malaise," says Mariuma.

Another telltale sign is dark urine, the color of tea or soda, he adds. But a marathon runner is unlikely to detect this signal mid-race.

How to prevent rhabdomyolysis — and what to do if it happens

Gradually training for a new activity, rather than jumping in at full tilt, can help reduce the risk. It's also important to stay hydrated not only during but also leading up to and after an activity that requires a lot of exertion, both experts advise. And if you're feeling at all unwell, stay home or at least keep your physical activity light, as intense activity while sick is a risk factor for the condition.

Tomazic, who is also a trail runner and ski patroller, acknowledges that the symptoms and risk factors — such as not properly fueling with water and food — can be easy to lose track of, especially mid-competition. "We — I say we because I do these things — we tend to push through pain; that's the mindset that we're encouraged to take," Tomazic says. "So sometimes it can be difficult to determine, 'Is this a pain that I should really listen to, or is it a pain that I can monitor, for now?'"

If you notice any symptoms of rhabdomyolysis, acting quickly is important, especially if you have risk factors for the condition, because "when it happens, it tends to happen over minutes to hours," says Mariuma. You should stop what you're doing, call for help and try to find some shade if you're outside on a hot day, Tomazic says.

Staying well hydrated helps dilute and flush out myoglobin, the muscle protein that can build up during rhabdomyolysis, and other molecules. But he adds, don't overdo it on plain water. Make sure you're getting electrolytes from your diet or sports drinks during intense athletic activities, since too much water without them can cause a dangerous condition called hyponatremia .

Rhabdomyolysis is primarily treated with IV fluids, which help the kidneys clear myoglobin and other substances released from damaged muscles. In cases where the kidneys have already suffered damage, some patients may receive dialysis, according to the Cleveland Clinic. More than 90% of patients who don't develop kidney damage from rhabdo survive, but the fatality rate rises to more than 20% with kidney injury, according to one study.

But overall, both Tomazic and Mariuma say that rhabdo shouldn't discourage you from running or participating in the physical activities you want to do. "Exercise-related rhabdo is rare … so I wouldn't use a tragedy like this as a reason to not do a marathon," says Mariuma. "Any activity out there, there are risks, and the only thing we can really do is learn the best ways to prevent them."