Cool! Thanks! I’ve actually been using that approach from the start. I use a pretty basic Suunto 5 Peak, but I always pair it with a chest strap and my own custom software to process .fit and .tcx files - thus I was able to determine heart rate zones quite precisely (LTHR 175 - MAX HR 185). Managing the raw data myself lets me feed the algorithms properly granulated metrics to decide about training steps. The chest strap is a game-changer, as is the ability to dig into your own raw data with Python instead of relying on basic aggregates. One cool thing I’ve noticed: I have access to a treadmill that displays my strap data in real-time. If I focus on form (not bending, proper arm swing, knee drive), my HR stays noticeably lower. But the real mind-blower was mindfulness. When I am fully present and don't let my thoughts wander, my HR drops by 4-10 BPM. I can actually keep myself in Z2 for a few kilometers where I’d normally drift into Z3 just by staying focused. Evidence based training for me is a key and chest strap is definitely best buck for the bang. Ex with the strap and Elite HRV app I can easily check how rested I am which is allegedly much better from that watches offer (as they simply cannot capture that precise data as HRV) and some watches are quite expensive while decent chest strap is less that 100 Eur.