On Nov. 1, a seemingly healthy 24-year-old woman from Pennsylvania, Rachel Apa, collapsed near the end of the New York City Marathon. She died later that day despite treatment, and her father told the New York Times that her death was linked to rhabdomyolysis, a condition in which damaged muscle tissue releases substances into the bloodstream that can injure the kidneys and sometimes the heart. Extreme exercise is one possible trigger. The city’s medical examiner was still investigating the cause.

Here’s what to know about the condition.

What is rhabdomyolysis?

Rhabdomyolysis is a process where the muscle cells break down and die, says Dr. Douglas Farrell, a nephrologist at Mount Sinai Hospital in New York City.…