Hi David,
first of all I want to thank you for this incredible tool, it is really amazing how many features you keep adding, a delight for data-driven people. I’ve noticed you’ve recently been working on the running side, which is very nice!
One metric I’ve been using is the so-called “running index”. To me, it is a bit like the estimated VO2max of Garmin devices, not so reliable absolute value, but the evolution correlates quite well with aerobic fitness (in my experience). As opposed to the Garmin VO2max estimate, it is given on a per-run basis (no averaging) and compensates for the hilliness of the route you’re running.
The Elevate plugin has some implementation of it. As it has some kind of copyleft license, maybe it would be possible to implement it without too much work.
Thanks in advance