Fitness tracking solutions

Hi! There's been a bit of a chat here about Bangle.js's built-in fitness tracking (or lack of), and I think this would be a really good thing to chat about so I can try and build something that handles general fitness tasks out of the box (but is easily extensible).

So I was wondering if any of you had any thoughts about this?

I'm thinking:

• On-watch Step/heart rate logging, every 10 minutes during the day (keep 1 week of history)
  
• GPS recorder able to log steps/HRM
  
• Ability to add extra data to logs (in addition to steps/hrm) via installed apps/widgets
  
• Modify BangleRun to use GPS recorder to reduce duplication
  
• Add on-watch graphs for recorded data
  
• Allow Gadgetbridge to read the logged health data if it hasn't been connected to the watch for a while
  
• Export of health data? GPS traces via GPX/KML is easy, but I'm not sure whether there's a format that already exists for health data that other apps will accept?