Strava totally ruined the running challenges as a whole.  Not only did they eliminate the longer challenges because they were too hard for some people to achieve (can't make anyone feel bad, right?), but they add walks as a permitted activity type to the running challenges they kept.  At least with running activities, they have a system that automatically flags some of the unrealistic activities.  It still misses a lot, but does screen some of them out.  They don't have that with walks, so the challenge leaderboards get totally flooded with bad GPS data, people recording drives, motorcycle rides, plan flights, etc... as walks.  Right now, you have to go back a ton of pages on the leaderboard to find the first legitimate "run" activity.  @Jane11 @Scout