You probably know someone who has trained for a first marathon.
The long weekend runs, the new shoes, the careful hydration. Most people cross the line and tell the story for years. A small number never make it to the end.
Rachel Apa, 24, collapsed near the 24-mile marker of the New York City Marathon in Central Park on Sunday, November 1, 2026.
Her father, Steve Apa, told NBC News that doctors said she died of rhabdomyolysis, a diagnosis they described as extremely rare.
Also read: New melanoma shot built from your own tumor cuts recurrence by 42%
A bystander performed CPR before marathon medical staff reached her with a defibrillator. She was taken to Mount Sinai Hospital in critical condition and died hours later. Her father called the loss "unfathomable."
Apa was a former Division I field hockey player at Bucknell University. She was running her first marathon, in memory of her grandfather and to raise money for the Parkinson's Foundation.
What does rhabdomyolysis to the body?
Rhabdomyolysis is the sudden breakdown of skeletal muscle. When muscle fibers rupture, they release their contents into the bloodstream, including a protein called myoglobin.
According to the Cleveland Clinic, about 26,000 people in the United States develop the condition each year.
Also read: The surprising reason cottage cheese may be one of the best bedtime snacks
The danger lies downstream. In large amounts, myoglobin can clog and poison the kidneys as they try to filter it.
That can trigger acute kidney injury, dangerous shifts in the body's electrolytes and, in the most serious cases, heart rhythm problems or death.
Exercise is only one trigger. MedlinePlus, the US National Library of Medicine's consumer health site, lists severe exertion such as marathon running alongside trauma, drug reactions, seizures, overheating and dehydration.
Most at risk and what warning signs to watch for
A clinical review in Sports Health describes the hallmarks of exertional rhabdomyolysis as muscle pain, tenderness, weakness and swelling after hard physical activity.
Also read: Feeling stressed all the time? Here's what may be happening to your immune system
Darkened urine, often tea or cola-colored, is another classic sign.
The review flags sudden jumps in training, heat, poor conditioning and dehydration as common risk factors. Taking NSAIDs or stimulant medications around hard exercise also raises the risk.
The paper estimates the condition at about 29.9 cases per 100,000 person-years in military data.
Doctors describe the muscle pain as feeling out of proportion to the effort. Dark urine often appears in the hours or days after the workout or race.
Also read: What happens to your body when you eat pomegranate seeds every day
Anyone noticing those signs after hard exercise should contact a doctor without waiting it out, especially if urine output drops.
What this means for people running their first long race
For most runners, finishing a marathon is tiring, not dangerous.
The risk of rhabdomyolysis rises when someone pushes well past what their training has prepared them for, runs in the heat, is dehydrated, or uses anti-inflammatories to mask pain.
First-timers and people coming back after a long break sit closer to that line than many realize.
Also read: Popular kale chips recalled over potentially toxic heavy metal contamination
If muscles ache deeply for days and urine turns dark after a long effort, the right next step is a call to a doctor, not a rest day at home.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.