Let's all just agree: Ultramarathoners are insane superhuman. A mere 26.2-mile run doesn't satisfy them. Instead, they chase adrenaline for hundreds of miles, sometimes for weeks on end.
And while running has undeniable benefits -- it improves your joint health, builds endurance, even boosts your sex appeal and keeps you feeling sexy -- scientists say that extreme long-distance running can be taxing on the body, including the brain.
Researchers at the University Hospital of Ulm in Germany found that the brains of runners who participated in the 2009 Trans Europe Foot Race -- an ultramarathon that covered nearly 2,800 miles in 64 days -- temporarily shrunk throughout the course of the race.
Dr. Uwe Schütz and his research team followed 44 runners during the nine-week race across southern Italy into Norway. Using a portable MRI scanner, the researchers scanned the runners' joints, limbs and organs every three to four days for the entire race, Smithsonian Magazine reported.
The researchers found that 13 of the runners who agreed to additional pre- and post-race brain scans had lost an average 6.1 percent of gray matter volume by the end of the race.
Schütz announced these findings -- which, given the study's small sample size, are considered preliminary and far from definitive -- during the Radiological Society of North America's annual meeting in Chicago last week. He did not immediately reply for The Huffington Post's request for comment.
While fatigue and undernourishment may play a role in the loss of volume, Schütz thinks that lack of brain stimulation could be a major factor, since the athletes are solely focused on the road ahead for 64 days, according to the New Scientist.
Eight months after the race, however, follow-up brain scans revealed that there were no lasting effects on the brain and that the athletes' gray matter volume had returned to normal levels.
"Despite substantial changes to brain composition during the catabolic stress of an ultramarathon, we found the differences to be reversible and adaptive," Schütz said in a press release. "There is no lasting brain injury in trained athletes participating in ultra-running."
And, according to Dr. Roger Woods, professor of neurology at University of California, Los Angeles, shrinking gray matter isn't always detrimental to the brain or body.
"I think this study very nicely illustrates the faulty logic of concluding that an activity that thins brain gray matter is necessarily bad for the brain," Woods told HuffPost. "The fact that the gray matter returned to normal with time clearly distinguishes this from a disease process such as Alzheimer's disease, where thinning is relentlessly progressive."
Researchers also found that all 44 runners in the study experienced cartilage breakdown in the joints at about 1,550 miles into the race. Amazingly, after that point, the cartilage began to recover as the athletes continued to run.
"It was thought that cartilage could only regenerate during rest," Schütz told New Scientist. "We have shown for the first time that it can regenerate during running."
Normal marathon runners, who embrace the one-day challenge of running over a couple dozen miles, won't have to worry about these extreme body and brain changes. According to Schütz, those athletes won't experience the same physical toll.
This story was updated to include comment from Dr. Roger Woods, professor of neurology at the University of California, Los Angeles.
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