Why doesn't your Algorithms for measuring VO2 and productivity take into account elevation data in trailrunning. Several times now I've experienced going from running at flat roads for a period and 
seeing my productivity measurement and VO2 number going up, then upon returning to trailrunning in forest and really pushing myself to the limit, evident in my heartrate data, receiving a "cold bucket of water" from Garmins Algorithms showing right away a decrease in VO2 number and productivity. Today after 12,5 km of trailrunning, running the fastest km-splirs (4:55) for a couple of Months and inowing that I'm absolutely on track with my performances, I get a decrease in VO2 (51 ) and I'm deemed unproductive in spite of running 6 km Yesterday evening, just 18 hours ago, and meeting my stepgoal just about every day.
I️t's weird that the biggest producer of sportswartches haven't got a clue to different types of running. My watch is Forrunner 645. It's even in the title "For runner", but it only applies to flat roads running apparently.
You should do something about this. Take into account elevation data. Take into account a distinction between trail and normal running. Take into account heartrate data. And changing my status to "unproductive" the very day I do a 12.5 km trailrun in record time, a 53 year old man. It's unfair. And it is in itself and unproductive use of gamification. Now I'm not stupid and I am able to think for myself, so it will not decrease my motivation for excercising, but it is counterproductive none-the-less. I should have been padded on my shoulder with a: Great going today.
I'm sharing my Garmin account here, for the sake of clarity. This could give you an idea of my excercise schedule and why I think something is dead off with your algorithm.
Check out Jakob M. Larsen on Strava
www.strava.com/.../63895705
