Apple Watch Series 12 vs Garmin Fenix 9 Pro: Some big HR and calorie differences

The Apple Watch Series 12 and Garmin Fenix 9 Pro are two highly advanced smartwatches that excel in heart rate tracking and calorie counting. The watchmakers have implemented new Health Sensing System technology that reportedly provides up to 60 times more frequent heart rate measurements compared to previous models.

During a 40-minute strength training session, the Apple Watch Series 12 recorded an average heart rate of 125 bpm, while the Garmin Fenix 9 Pro showed an average of 132 bpm. The heart rate difference of seven beats per minute slightly exceeded the 5 bpm margin of error, but not by much. The authors believe that as both watches adapt to their respective users, their heart rate tracking algorithms will improve to deliver increasingly accurate results.

However, when it comes to calorie expenditure, the gap between the two wearables is far more significant. The Garmin Fenix 9 Pro reported a calorie burn of 340 kcal during the session, whereas the Apple Watch Series 12 logged a lower tally of 242 kcal. The 88 kcal discrepancy is the equivalent of consuming a small apple or a couple of spoonfuls of ice cream.

While smartwatch calorie tracking is inherently less precise than other health metrics, an 88 kcal difference represents more than a 20% margin of error, which is a noteworthy concern.

The authors stress that it's essential to keep in mind that each watch operates with a unique algorithm, and some level of variability is expected. Nevertheless, the substantial calorie count disparity between the two devices warrants further investigation. The authors plan to conduct additional testing of the Apple Watch Series 12 across various workouts and compare it to other wearables to assess the accuracy of Apple's heart rate and calorie tracking claims over time.