... FACT.
In the BBC's The Truth About ... series, Dr Michael Mosley went to see a university professor who has shown that over a given distance, walking exerts more force on your knees than running does. It's due to an increased contact time with the ground.
Watch here (scroll forward to about 38 mins) bbc.co.uk/iplayer/episode/b...
(UK only, sorry!)
Cheers
John
PS the whole episode is worth watching. '10,000' steps has no evidence behind it - it was a marketing gimmick for the 1964 Tokyo Olympics.