The Fenix 5+ has several sensors including a heart rate sensor. Why is it still necessary to use a chest heart rate monitor in order to get scores on lactate threshold and HRV? Or is there a widget that can measure this with the sensor on the watch?
Lots of good answers here on what can be a tricky subject.
To calculate Lactate Threshold, the Firstbeat analytics engine built into your Garmin device needs the HRV data, relatively easily available from a chestbelt, where each beat is pinpointed with the electrical signal - getting that reading during that level of intense physical activity from an optical sensor (especially one bouncing around on your wrist) hasn't been solved yet.
Its to do with how the Firstbeat algorithms work and the level of accuracy they currently require. So the stress score can be calculated with the current Garmin OHRM because it's good enough to pick up a decent HRV signal when you're moving around. It's not good enough to capture a high fidelity HRV signal when you're running however, which is why you still need to use a chest strap to get performance metrics like lactate threshold.
Because they are just data based algorithms Firstbeat may one day figure out a way to calculate some of the performance metrics that still require a chest strap. It wasn't that long ago that getting a "stress score" required doing a 1 minute test with a chest strap every day.
