As athletic achievements go, running a marathon is towards the top of the list. But even this isn’t challenging enough for ultra-marathoners, who run races longer than the standard 42.2. kilometers (26 miles). The 2009 Trans Europe Foot Race, for instance, involved running from Italy to Norway—4,500 kilometers over 64 days.
Such extreme feats are a good excuse to study how stress affects the human body. To this end, researchers at the University Hospital of Ulm in Germany followed 44 runners during the 2009 Italy-to-Norway race. After every 900 kilometers, they measured the changes in a runner’s body using portable MRI scanners, as well as blood and urine tests.
They found that, for the first 2,500 kilometers, runners’ cartilage—the shock-absorbing material found between bones—degraded. But after that, the cartilage actually started to recover.
“It was thought that cartilage could only regenerate during rest,” lead researcher Uwe Schütz told New Scientist. “We have shown for the first time that it can regenerate during running.” The researchers revealed their results at the annual meeting of the Radiological Society of North America.
Extraordinarily, they also found that a runner’s brain shrinks as much as 6% by the end of the race.
Exercise is considered to be beneficial to the brain, staving off depression and dementia. A shrinking brain is not generally considered a good thing. Ulm researchers are not sure yet why the brain shrinks after very long-distance runs, but it may simply be a result of extreme fatigue and poor nourishment.
Among the ultra-marathoners, the area of the brain that shrank the most is involved in visual processing. The lack of stimulation—simply looking at roads for 64 days straight—may have something to do with it. It could be the result of a coping mechanism to reroute valuable energy to parts of the body that need it more.
Fortunately, all of the runners recovered their original brain size completely after six months. And those who just run a single marathon—or, like most of us, jog much shorter distances—won’t experience the same effects.