[ToFundorNot]

I skimmed the report, they break down the % of people still running. They took x-rays and measured the space between the joints amongst other tests to see how much wear/damage occurred in the 18 year period. In both the control, and the runners group there were runners (17% vs 97.8%). By the end the runners group still had 55.6% running vs 3.8%.

Unfortunately they didn't break down the km's ran to classify the individuals. Also The runners group was almost more likely to do 'vigorous exercise'.

To answer your question, they did continue to classify as runners even if they stopped (and almost half did stop).