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lala-zarate
User level: Level 1 (4 points)

New Apple Watch Series 12 does not record heart rate for the first 9 minutes of an Indoor Run

New Apple Watch Series 12 (GPS), 42mm Aluminum, model MJFQ4LS/A, watchOS 27.0.1 (24R365).


Today my run started at 9:08, total 11 minutes 34 seconds, 1.16 miles. The heart rate chart is blank until 9:17 to 9:18, then it jumps to 150 to 170 BPM. Post workout heart rate reads normally.


I already checked all settings. Workout Low Power Mode is off. Battery Low Power Mode on the watch is off. Heart Rate is on. Fitness Tracking is on.


This is a new watch. Is this a known bug, or a defective sensor?



[Edited by Moderator]

Posted on Oct 11, 2026 6:38 AM

2 replies

WheelieNick
User level: Level 9 (74,110 points)

Oct 11, 2026 7:29 AM in response to lala-zarate

Hi there


Please try this


  • Tighten the Band for Runs:  Tighten your watch band by one extra notch specifically for your runs, or shift it about an inch higher up your forearm away from the wrist bone to secure a flush fit against the skin. Warm Up Before Starting the Workout App: Give the watch a moment to establish a solid heart rate baseline while you are walking or stretching, then tap the start button on the Workout app.
  • Reset Fitness Calibration Data: Go to the Watch app on your iPhone -> Privacy -> tap Reset Fitness Calibration Data. This clears out old motion mapping parameters and forces the watchOS 27 algorithm to recalibrate tracking accuracy to your running stride


Grant Bennet-Alder
User level: Level 10 (148,617 points)

Oct 11, 2026 8:00 AM in response to lala-zarate

I saw a similar issue, but do Not consider it a software or hardware defect.


I first tried (with limited success) checking my heart rate (invoking the watch heart rate App) a moment before I started a workout, to be sure the watch had a good baseline to follow. That helped a little, but one MORE thing to remember. Not really a satisfactory work-around.


Next workout, promptly forgot to do that, and the heart rate was initially blank, and I was annoyed. When I looked over at my wrist, I saw the watch was moving about as I moved. Rather than stopping to tighten the band, I just pushed the watch up my arm until it was still (relative to my arm).


That resulted in dramatic and immediately better results.


I did not need to recalibrate anything.

Originally posted at discussions.apple.com/thread/256374192