As for #privacy..
- People should be in full control of what they share
- They might share first to their Circle or Club. A group of friends or local sports club
- Clubs might share generalized non-PII metrics
- Then there are public Challenges. "The London Marathon", "Climb the Mont Blanc", "My town's yearly local sports event" where it is perfectly fine if they are public, and you can say "I participated in the Nijmegen 4-day walk and improved my last year's record"