Marathon Handbook reports on rhabdomyolysis, a condition caused by muscle damage during intense exercise. It can lead to kidney injury and other complications. The condition gained attention after Rachel Apa's death during the NYC Marathon.

Rhabdomyolysis occurs when muscle fibers break down, releasing proteins into the blood. This can harm kidneys and disrupt heart rhythm. The U.S. military sets a CK level of 5,000 for diagnosis after strenuous exercise. Read more culture coverage.

Risk factors include unaccustomed intense exercise, heat, and dehydration. A study found Black soldiers with sickle cell trait had higher risk. Symptoms include severe muscle pain, swelling, and dark urine. Related: Marathon Runner Dies After Collapsing in NYC Marathon.

This original Runner World brief is based on reporting from Marathon Handbook. Visit the source for its complete reporting, context and any later corrections.