Coding an app for running and cycling ?

@myownself About HR zones, definitions may differ slightly in terms of percentage, but not that much, I can make a bit of research to check what's the most commonly accepted as a standard. Maybe the incertainties you spoke about are related to the definition of the max HR which can be calculated (pretty imprecisely, whatever the method) or can be "obtained" from hard exercice (but here too it's difficult to get it right and reach 100%). I suppose it's still possible to offer the possibility for people to tweak their own zones the way they want.
About the ON/OFF/external HRM, sorry I wasn't clear about it. I do agree that it should be in the global settings of the bangle.js, not in the app. Actually, Gordon said that it's a good idea, and encouraged me to code this, but as mentionned before, I don't code.
All the great stuff about the different types of run could appear either in the bottom left corner with taps or have their own screen after a swipe up or down (to know how many intervals/time/kms are left, what's the resting time, duration left for the training and so on).
Are you doing a git or something where people can contribute to the code (for the runner app) ?
I think that if an app can cover all what we spoke about here, it would cover the needs for at least 90% of runners. The remaining 10% that need VO2Max and this kind of things, well they should go for an expensive watch.
The last thing I can think of (for now) is a "marathon option". It would be the same as in "distance run" (give HR, distance, elapsed time, speed), but also gives a little extra with an estimation of the remaining running time if the pace is constant.
Actually, since the beginning I'm wondering if all these calculations at the same time are too much to handle for the bangle.js if it lasts for more than an hour.