Long-distance runners’ brains shrink.

Not that New Scientist wants you to worry about what your exercise routine could be doing to your memory. Just that researchers have found ultra-marathoners’ brains are measurably smaller after a race:

Uwe Schütz at the University Hospital of Ulm in Germany and his colleagues have spent the last six years finding out. In 2009, they followed a group of 44 runners as they ran the nine-week race across Europe. The team took a portable MRI scanner with them, and periodically scanned the legs, feet, heart, brains and cardiovascular systems of the athletes, as well as taking blood and urine samples.

Scanning feet and leg joints every 900 kilometres, Schütz and his team measured the amount of water that was released from the shock-absorbing cartilage between the bones – a sign of whether cartilage is breaking down. They found that the runners’ cartilage seemed to degrade during the first 2500 km of the race.

But after that distance – around 60 marathons – the cartilage seemed to recover, says Schütz, who presented the findings at the Radiological Society of North America annual meeting in Chicago this week. “It was thought that cartilage could only regenerate during rest,” he says. “We have shown for the first time that it can regenerate during running.”

A runner’s joints aren’t the only parts of their body affected. Earlier analyses of the same runners revealed that their brains seemed to temporarily shrink in size by 6 per cent over the course of the race.

The loss may simply be the result of extreme fatigue and undernourishment, but Schütz thinks it could be caused by lack of stimulation. One of the four brain regions that seems to be particularly affected is known to be involved in visual processing.