On-device HRM is unreliable is most of the cases

Number:rdar://32149354 Date Originated:
Status:Open Resolved:
Product:watchOS + SDK Product Version:3.2 (14V249)
Classification: Reproducible:Always
Apple Watch on-board heart rate monitor rarely provides correct (or any) heart rate measurements while doing active sports. Any activity that involves arm motion makes Apple Watch unable measure heart rate. Examples of such sports are: running/jogging, bike riding on uneven surface, playing soccer. 

Sometimes, when activity becomes "smoother" Workout.app fails to resume heart measurements until activity is ended, thus failing to collect any HRM data after grey HR measurement was displayed.

Furthermore, paired AirPods seem to interfere with external/BT HRMs, thus making it impossible to record/view HR measurements using Apple Watch. See rdar://32149140 for details.

Steps to Reproduce:
1. Wear Watch on right hand (whether this is contributing factor is unknown)
2. Start Run or Cycling workout
3. Run (or ride bike on uneven surface)

Expected Results:
Watch should measure heart rate at least majority of activity time, ideally all the time.

Actual Results:
Watch rarely is able to measure heart rate. In some cases first failed attempt to get measurement lasts till the end of activity (grey HR measurement in Workouts.app) 

Walking, stationary bike exercise or riding road-bike on extremely smooth surface (until first pothole) seem to not interfere with built-in HRM.

Tested on Apple Watch Series 2 Stainless Steel 42mm and Original Stainless Steel 42mm. Both yield same results. Watches worn on right hand.


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