In a first such experiment, researchers tracked 44 long-distance runners covering 4,500 km in Europe, recording real-time cartilage regeneration in them as they hit the ground.
Using a mobile MRI truck, researchers followed runners for 4,500 km through Europe to study the physical limits and adaptation of athletes over a 64-day period.
The results showed that with an exception to the patellar joint (one of the knee joints), nearly all cartilage segments of knee, ankle and hind-foot joints showed a significant degradation within the first 1,500 to 2,500 km of the race.
"Interestingly, further testing indicated that ankle and foot cartilage have the ability to regenerate under ongoing endurance running," aid Uwe Schutz, specialist in orthopaedics and trauma surgery at the University Hospital of Ulm in Germany.
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," he noted.
The MRI investigations of the soft tissues and bones of the runners' feet showed a significant increase of the diameter of the Achilles tendon.
"We found no relevant damage to bone or soft tissues in the 44 runners. The human foot is made for running," Dr Schutz noted.
The researchers also looked at how long-distance running affects brain volume.
The analysis revealed no significant differences in gray matter volume.
At the end of the race, MRI of the brain revealed about a 6.1 percent loss of gray matter volume in the runners.
After eight months, gray matter volume had returned to normal levels.
Although the finding on gray matter volume loss while running is astonishing, it is no cause for alarm.
"Despite substantial changes to brain composition during the catabolic stress of an ultramarathon, we found the differences to be reversible and adaptive," Dr Schutz pointed out.
The Trans Europe Foot Race (TEFR) took place from April 19 to June 21, 2009.
It entailed running 4,487 km starting in southern Italy and ending in the North Cape in Norway without any day of rest.
Forty-four of the runners (66 percent) agreed to participate in the study.
The research team's most important tool was a 1.5 Tesla MRI scanner mounted on a mobile unit, the only one of its kind in Europe at that time.
Each participant was scanned every three to four days, resulting in 15 to 17 MRI exams over the course of the race.
The findings were presented at the annual meeting of the Radiological Society of North America (RSNA) on Sunday.
