Even though watchOS 4 supports all watch models, the original device (also called Apple Watch Series 0) featuring Apple's S1 chip does not support any of the expanded heart rate analytics provided by the new software.
Heart rate sensor
Apple touted a few changes to heart rate tracking for Apple Watch during their September event. Some had expected these features to come solely to the new Apple Watch Series 3, but they actually come to everyone, courtesy of watchOS 4.
A new medical study from Stanford University focusing on consumer fitness tracker reliability, published Wednesday in the Journal of Personalized Medicine, has crowned Apple Watch the king of heart rate monitoring while pointing out shortcomings in its calorie counting feature.
“People are basing life decisions on the data provided by these devices,” Euan Ashley, DPhil, FRCP, professor of cardiovascular medicine, of genetics and of biomedical data science at Stanford said in a statement.
The study included 29 male and 31 female volunteers who wore several fitness trackers like Basis Peak, Fitbit Surge, Microsoft Band, MIO Alpha 2, PulseOn, Samsung Gear S2 and Apple Watch. The study pitted the wearable gadgets against FDA-approved equipment.
The participants were asked to complete a total of 80 physical tests, including such activities as cycling, running and walking. They compared data against an FDA-approved 12-lead electrocardiograph for measuring heart rate and clinical-grade indirect calorimetry, which determines calories burned by measuring oxygen and carbon dioxide expelled when breathing.
Heart-rate monitoring via Apple Watch achieved the highest accuracy across measured modes of activity with an error rate of two percent, followed by Basis Peak and Fitbit Surge.
Samsung's Gear S2 had the highest heart rate error rate at 6.8 percent.
Researchers set an acceptable error rate at five percent, meaning Samsung's device fell just outside the study's acceptable buffer.
All fitness devices they tested fell short in calorie counting.
In terms of determining the amount of calories burned, Fitbit's Surge was the most accurate device with an error rate of 27.4 percent. PulseOn was the least accurate tracker in terms of calorie count with an astounding error rate of 92.6 percent. Apple Watch had an error rate near 40 percent while Microsoft Band came in at around 33 percent.
Low-impact activities like sitting caused the most inaccuracies with an average error rate of 52.4 percent compared against high-impact activities, such as walking and running.
This is due to the differences in how people exercise. “People are so variable,” Ashely said. “Some people walk smoothly and others waddle along, and that has an impact."
“The heart rate measurements performed far better than we expected, but the energy expenditure measures were way off the mark,” she added.
“The magnitude of just how bad they were surprised me.”
Each of the tested devices uses its own proprietary algorithm for calculating calorie burn, which could explain the wildly differing readings in terms of energy expenditure rates.
The Apple Watch is 97% accurate at detecting common abnormal heart rhythms, according to a study by the University of California, San Francisco. Heartbeat measurement app Cardiogram began the study with UCSF last year to determine whether or not the wearable could detect an oncoming stroke.
The study consisted of 6,158 participants, most of which had normal EKG readings and 200 of which had been diagnosed with paroxysmal atrial fibrillation (or an abnormal heartbeat). Engineers trained a deep neural network to identify the abnormal heart rhythms from Apple Watch heart rate data.
Testing their findings against 51 in-hospital cardioversions (a procedure that restores the heart's normal rhythm), the team says its neural network correctly identified irregular heart activity with a 97% accuracy rate. The results hold promise for the long-running effort to detect and prevent strokes in the future.
Atrial fibrillation, the most common abnormal hearth rhythm, is believed to cause 1 in 4 strokes. Cardiogram co-founder Brandon Ballinger says two-thirds of these types of strokes can be prevented with inexpensive drugs. The team plans to continue its eHealth study and further validate its neural network.
Currently, you can protect your Apple Watch with a passcode or set it to automatically unlock itself whenever you unlock your iPhone. But if a newly published patent application from the Cupertino firm is anything to go by, the wearable device may soon be able to seamlessly identify the owner with its built-in heart rate sensor.
As published by the United States Patent & Trademark Office (USPTO), the invention titled “User identification system based on plethysmography” proposes using a pulse oximeter to intelligently identify biometric characteristics of a user's vasculature.
Currently, your Apple Watch learns about calories you burn by applying some math magic to your heart rate readings and values obtained from its sensors.
The method provides reasonably accurate estimates of resting/active calories. However, even more precise calorie-burning readings could come soon if Apple decides to enable the hardware feature which can reportedly measure oxygen levels in your blood.
As an iFixit teardown has identified, the Apple Watch heart rate sensor has onboard hardware for detecting blood oxygen saturation.
In addition to fixing performance issues and a number of problems related to the accuracy of fitness tracking, the first software update for the Apple Watch seem to have introduced an unintended bug.
The affected owners have flocked to Apple Support Communities and MacRumors' forums to report that the device is now capturing their heart rate readings less frequently than before after updating to Watch OS 1.0.1.
Apple says the device's heart rate sensor should capture heart rates every ten minutes throughout the day — even more frequently during workouts — but there are now noticeably larger gaps of time between data, some as long as an hour or more.
There's no two ways about it: even under the most ideal of conditions, the Apple Watch may not be able to get a reliable heart rate reading every time for everybody. Now, our recent overview of the Apple Watch's heart rate sensor provided a good starting point for enthusiasts wishing to learn more about the feature. It gives you a better idea of the intricacies and benefits of the custom-designed hardware feature marketed primarily to fitness aficionados.
But the truth is, it's been designed for everyone, really. It's something every Watch customer will be using without even being aware of it, simply by wearing the device (for those wondering, the average human heart rate is about seventy-two beats per minute).
On the back of the Watch is a specially designed sensor protected by a ceramic cover with sapphire lenses, with infrared and visible-light LEDs and photodiodes detecting the amount of blood flowing through your wrist at any given moment.
Knowing your heart rate helps the Watch determine your intensity level during workout while improving the accuracy of your active calorie burn measurements. Therefore, knowing the sensor's limitations and pitfalls is important.
Luckily, there are some things you can do to help the Watch get the most consistent and best heart rate readings possible. Here are five sound tips regarding using this feature optimally and with minimal disruption.
A support document Apple published earlier this month contains a number of interesting tidbits and nice-to-knows regarding the Watch's built-in heart rate monitor. We thought it'd be useful to give you a quick summation of the technologies the wrist-worn device uses to provide accurate readings of your heart rate.
The document also confirms that the Watch can connect wirelessly to external heart rate monitors such as Bluetooth chest straps for even more precise readouts.
All in all, Apple's done a fine job outlining in Layman's terms the tech and the sensors that measure a user's heart rate, a feature many reviewers have described as seamless. In Apple's parlance, it just works and here's exactly how it works.