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CHICAGO -- A study of ultramarathoners who ran the whole of Europe demonstrated that critical leg joints seemed to self-heal even as the runners covered about 70 km (42 miles) a day, researchers said here.

With the exception of the patellar joint, nearly all cartilage segments of knee, ankle, and hindfoot joints showed a significant degradation within the first 1,500 to 2,500 km of the race. But with continued running, the deficits resolved, according to Uwe Schütz, MD, of University Hospital of Ulm in Germany, and colleagues.

Action Points Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

A study of ultramarathoners who ran the whole of Europe demonstrated that critical leg joints seemed to self-heal even as the runners covered about 70 km (42 miles) a day.

Note that the study also found that at the end of the race, MRI of the brain revealed about a loss of gray matter volume in the runners that resolved 8 months post race, showing that there is no lasting brain injury in trained athletes participating in ultrarunning.

"Interestingly, further testing indicated that ankle and foot cartilage have the ability to regenerate under ongoing endurance running," Schütz told MedPage Today at Radiological Society of North America (RSNA) meeting. "The ability of cartilage to recover in the presence of loading impact has not been previously shown in humans. In general, we found no distance limit in running for the human joint cartilage in the lower extremities."

Using a mobile truck with an 1.5-Tesla MRI scanner that Schütz drove -- "we didn't have enough funding to hire a driver," he acknowledged -- the researchers followed 66 runners participating in the Trans Europe Foot Race, which goes for for 4,500 km from the tip of the toe of Italy, through Austria, Germany, Denmark, Sweden and finally reaching Nordkapp (North Cape) in the Norwegian Arctic. The race took place over over 64 days from April to June 2009.

They ran tests in 44 of the runners who agreed to undergo the observations and testing.

Each participant was scanned every 3 to 4 days, resulting in 15 to 17 MRI exams over the course of the race. More than 1,500 MRI scans were completed during the month-long study. The runners were also randomly assigned to additional examinations, and protocols were created for daily urine, blood, and other tests.

Nearly all cartilage segments showed a significant initial mean T2 signal increase within the first 1,500 km of the run:

Ankle: 25.6%

Subtalar joint: 20.9%

Midtarsal joint: 26.3%

Ankle 25.6%

Subtalar joint: 20.9%

Midtarsal joint: 26.3%

Femorotibial joint (FTJ): 25.1% to 44.0%

The authors noted an "unexpected secondary T2* decrease" in ankle (-30.6%) and hind-foot joints (-28.5% and -16.0%), but not in the FTJ. They also reported a significant loss of cartilage thickness in the FTJ, but not in the other joints.

"A side dependent, positive relationship between muscle volumes of the thigh and cartilage T2* at baseline could be found in the FTJ," they wrote. "Osteochondral lesions were detected, however all were already present at baseline and showed no changes throughout [the race]."

They also pointed out that reasons for stopping the race were not associated with joint problems.

"The human foot is made for running," Schütz said.

The researchers also looked at how ultramarathon running affects brain volume. Baseline comparison of race participants and controls revealed no significant differences in gray matter volume. At the end of the race, MRI of the brain revealed about a 6.1% loss of gray matter volume in the runners. But 8 months post race, 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," he said. "There is no lasting brain injury in trained athletes participating in ultrarunning."

For non-athletes, the results may indicate that most parts of human cartilage have the capacity to recover in the presence of extreme physical stress, and that human joint cartilage may have "a high regenerative potential," the authors stated.

"This is exceedingly interesting work," said Salomao Faintuch, MD, clinical director of vascular and interventional radiology at Beth Israel Deaconess Medical Center in Boston, and assistant professor of radiology at Harvard Medical School.

"It gives us a idea of the limits of human endurance and how far humans can go in extreme sports," added Faintuch, who served as the RSNA session moderator. "We are able to visualize these changes without new technology, which gives us a view of something we had never before been available. It gives us an understanding of how the human body behaves and reacts to these circumstances."

He said that Schutz' findings might explain the survival of ancient human hunter-gatherers who were forced to continually move about to survive. If their legs had given out, they might have just been left where they fell, he suggested, indicating that today's humans are representatives of the survival of the fittest.

"We are probably not descendents of those that didn't make it," Faintuch suggested.