Some Apple Watch owners have expressed their disappointment over the Apple Watch's inability to provide accurate heart rate readings while exercising, raising doubts about Apple's claim that the Apple Watch is the most accurate wrist-based heart rate monitor to date.

Apple Watch owners have taken to the Apple Support Forums and around a dozen threads on Reddit to point out that the Apple Watch generates heart rate readings completely off the mark.

The problem arises during two kinds of exercises: weightlifting and high-intensity workouts such as Crossfit. Some users also claim their Apple Watch registers extremely inaccurate readings while doing exercises recommended by Apple's Workout app, such as walking, running and biking.

"I have been using my Apple Watch to track my workout sessions and for (the) past few days I have noted that whenever I am doing intense workouts where there is a lot of hand movements like P90X3 or Insanity, the Apple Watch heart rate sensors gives wrong readings," says one user. "For example, at the peak of P90X3 workout when I am totally out of breath, the Apple Watch heart rate sensor will show heart rate as 60 or 70, but the heart (rate) should be in excess of 150+."

The user adds that he tried using the Apple Watch on one wrist and a Polar smartband with a heart rate monitor strapped to his chest to see how both devices would compare. At the peak of the workout, the Polar was showing a reading of 160+ bpm while the Apple Watch was around 70 to 80. He says he was sure the Apple Watch was fit snugly around his wrist so it wasn't moving around loosely to cause an inaccurate reading. His sentiments are echoed by other exercisers.

"I go back and forth between using my (Apple Watch Sport) and my Polar (with chest strap) during workouts. My Polar will read accurately, but my AWS will frequently read 60ish bpm while working out and I can clearly feel my heart rate elevated," says one Redditor. "I know the Apple Watch is supposed to be nearly as accurate as an EKG, but I have nowhere near that accuracy. I have my watch as snug as I can, which is a tiny bit loose because one hole smaller and it's way too tight, but even when I hold the watch firmly against my wrist, it reads poorly."

Apple says the Apple Watch tracks the user's heart rate using a method with an overly fancy name: photoplethysmography, where the amount of blood flow to the wrist is analyzed by tracking how much green light is absorbed. This is all based on the fact that blood is red because it absorbs green light, and the more green light is absorbed, the more blood flows to the wrist and the higher the heart rate should be.

However, even Apple admits this method has limitations, which are also inherent in other wrist-based heart rate monitors. This is why Apple recommends that people who have wrist tattoos use a chest strap companion with the Apple Watch. Weightlifters aren't also very lucky, since lifting weights will constrict the veins on the wrist and affect the Apple Watch's ability to accurately make heart rate readings.

Apple also says that the Apple Watch will not record readings during irregular motions. It specifically mentions boxing as an example, but Crossfit and those high-intensity Beachbody workouts aren't very rhythmic either, which may account for the user complaints surfacing on the Internet.

One user says he pairs his iPhone with a $199 Jabra ear monitor and tracks his heart rate via the Endomondo app, which then sends it to his Apple Watch. It's not a convenient or cost-effective solution, but until Apple and the overall heart rate monitor industry advances the technology, users will have to make do with what's available.

Still, as one user points out, it's misleading for Apple to advertise the Apple Watch's heart rate monitor as highly accurate, since it is not even close when tracking heart rate for major workouts. The Apple Watch's fitness tracking abilities are designed not for casual exercisers but for the hardcore ones who like to monitor their stats. That means they most likely do weightlifting and high-intensity interval training exercises regularly, since these are widely considered the most effective forms of exercise.

"I was really counting on the (Apple Watch) having an acceptable (heart rate monitor) for my workouts (typically interval training — run/row/isometrics)," says one user. "($199) is a steep price to pay on top of the $700 I just shelled out for the Apple Watch. I have always used a Polar watch and chest strap HRM and was hoping to be free of the extra hardware."

Apple has yet to comment about the latest complaints.

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