[ellisv]

If your Garmin HRM can write data to the Apple Health app then it would use that HR data. Without measuring your lactate threshold, you don't really know what your zones are. Apple has a concept of "effort" which is a single rating for the entire workout and it'd be interesting to incorporate that.

[kccqzy]

Yes I like that concept of effort. My question basically boils down to whether the user-provided effort value should be used to calibrate the zones.