Those 26.2 miles can take even more of a toll on your body than you’d expect.
A new study from the Yale School of Medicine tested marathoners right after racing, and found that 80 percent of the runners had markers of kidney damage. Their stats were close to what you’d see in just-operated-on heart surgery patients, according to one researcher.
“You can’t differentiate [marathon runners] from someone who had a cardiac surgery, or a person in intensive care unit,” Chirag Parikh, a nephrologist at Yale and the lead author of the study, told Quartz.
The small study took a look at 22 people who have been running 13 mile-plus stints for at least five years. Researchers drew blood and urine samples of the athletes the day before and the day after their marathons.
The study concluded that, post-marathon, runners had levels of inflammatory chemicals and creatine (an acid created when muscles are worked) similar to those of patients with acute kidney injury.
Scientists explained to Quartz that running can increase body temperature, which can wear down muscles and cause inflammation.