Running a marathon sounds like a triumph of willpower. You train for months, put a “26.2” sticker on your car, and tell everyone it was “life-changing.” The part you skip is what happens after: shredded feet, raw skin, digestive failure, and maybe even a colon that wants revenge.

“Running a marathon is an incredible physical and mental achievement, but it’s also a demanding event that places unique stresses on the body,” Dr. Mariam Zakhary of Mount Sinai’s Department of Rehabilitation and Human Performance, told the New York Post.

In a 2024 study of more than 1,000 New York City Marathon runners, nearly 40 percent were injured during training, and about 14 percent got hurt mid-race. Those odds make the finish line look more like a medical waiting room.

Here’s how 26.2 miles can wreck you from head to toe, and sometimes, a little deeper.

1. Heel hell

Your plantar fascia, the ligament connecting your heel to your toes, acts as your foot’s shock absorber. Dr. Rock Positano of Mount Sinai’s Heel Pain Center says marathon stress can cause degeneration or even tearing. It shows up with stabbing pain in the heel or arch.

2. Stress fractures

Tiny cracks in the tibia, metatarsals, or navicular bones often appear days after a race. They hurt, swell, and make stairs feel like absolute hell.

3. Jogger’s nipples and skin chafing

Sweat and friction destroy skin, especially on the nipples, thighs, and underarms. Dermatologist Dr. Jacob Beer calls “jogger’s nipple” one of the most common marathon injuries, and yep, it can bleed through shirts.

4. Toe trauma

Repeated toe strikes inside shoes can cause blood to pool under the nails, known as subungual hematomas. They throb, turn black, and sometimes need to be drained.

5. Gut revolt

During long runs, blood flow gets pulled away from your digestive system toward your working muscles. Dr. Dana Zalkin, a gastroenterologist, says that redirection of blood flow can lead to cramps, nausea, or a sudden sprint for the nearest porta-potty.

6. Brain drain

Another 2025 study found marathoners experience a temporary reduction in brain myelin, the fatty coating that protects nerves. It usually recovers within two months, but the short-term fatigue is real.

7. Kidney overload

Extreme exertion can temporarily injure the kidneys. Overhydrating can also dilute blood sodium levels, leading to confusion or worse, a condition called hyponatremia.

8. The big C

A 2025 study found nearly half of seasoned marathoners had precancerous colon polyps, suggesting that endurance training may stress the gut in ways we don’t fully understand.

Exercise is still good for you. But marathons are a different beast. The line between “healthy” and “heroic” might only be a few blisters wide.