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Apple Watch performed well among the wrist devices in a 2019 treadmill study, but a Polar chest strap agreed more closely with ECG. That is useful evidence—not a current ranking of today’s watches: the study tested Apple Watch III and three older rivals, and wrist readings became less reliable as running speed increased.
What “heart-rate accuracy” means in this comparison
Apple Watch and most fitness watches estimate pulse optically. Green LEDs illuminate the skin, and light-sensitive photodiodes detect changes in blood flow. This photoplethysmography (PPG) estimate is different from a chest strap’s electrical sensing and from an electrocardiogram (ECG) used as a reference. Apple describes its sensor method and limitations in its heart-rate guidance.
The 2019 study reported Lin’s concordance correlation coefficient, which measures how closely readings agree with a reference. Its values are not percentages, so a coefficient of 0.96 does not mean “96% accurate.” Agreement in one activity also does not establish performance for other activities, models, or people.
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What the head-to-head study found
Cleveland Clinic researchers studied 50 healthy athletic adults during a treadmill protocol, comparing wrist devices and a Polar H7 chest strap with three-lead ECG. The sample excluded people with certain health conditions and wrist tattoos, so it does not represent every wearer.
#1 Best Overall
![Apple Watch Series 11 [GPS 46mm] Smartwatch with Jet Black Aluminum Case with Black Sport Band - M/L. Sleep Score, Fitness Tracker, Health Monitoring, Always-On Display, Water Resistant](https://m.media-amazon.com/images/I/416RQ0rtsUL._SL160_.jpg)
- A FULL-FEATURED HEALTH TRACKER—Apple Watch Series 11 gives you invaluable insights about your body, right from your wrist. Take an ECG anytime* and get alerts for a high and low heart rate or an irregular rhythm*—so you can stay closer to your heart. You can also view your overnight health tracking metrics with the Vitals app* and be notified of possible sleep apnea.*
- KNOW YOUR SLEEP SCORE—With advanced sleep tracking, Series 11 gives you a daily sleep score. It’s an easy way to help measure and understand the quality of your sleep, so you can make it more restorative.
- GET HYPERTENSION NOTIFICATIONS—Did you know that Series 11 can spot signs of chronic high blood pressure? By analyzing how your blood vessels respond to beats of the heart, it can notify you of possible hypertension.*
- SAFETY FEATURES—A smartwatch that puts your safety first. Series 11 can detect a hard fall or severe car crash, automatically help connect you with emergency services, and notify your emergency contacts.* Check In can automatically notify a loved one when you’ve arrived at your destination.
- A POWERFUL FITNESS TRACKER—With advanced metrics and motivating features like Pacer, Heart Rate Zones, training load, and Workout Buddy powered by Apple Intelligence from your nearby iPhone*—Series 11 is made to help everyone stay active, from runners and hikers to strength-training enthusiasts.
| Device tested | Agreement with ECG |
|---|---|
| Polar H7 chest strap | 0.98 |
| Apple Watch III | 0.96 |
| Fitbit Ionic | 0.89 |
| Garmin Vivosmart HR | 0.89 |
| TomTom Spark 3 | 0.89 |
These are the study authors’ concordance coefficients, not percentages, and apply only to the tested devices and protocol. The study found concordance of at least 0.85 for every device at rest. As treadmill speed rose, wrist-device agreement declined; at 8 and 9 mph, none of the wrist watches reached 0.70. Apple Watch had the highest agreement among the wrist watches at each tested condition.
The results have important limits: the protocol used indoor treadmill running, readings were recorded visually while participants held the handrail, and the researchers did not directly test brands against one another for statistical significance. The authors’ conclusion that a chest strap or Apple Watch III may be the best choice when accuracy is imperative refers to that study—not to current models or all workouts. See the study report.
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- A FULL-FEATURED HEALTH TRACKER—Apple Watch Series 11 gives you invaluable insights about your body, right from your wrist. Take an ECG anytime* and get alerts for a high and low heart rate or an irregular rhythm*—so you can stay closer to your heart. You can also view your overnight health tracking metrics with the Vitals app* and be notified of possible sleep apnea.*
- KNOW YOUR SLEEP SCORE—With advanced sleep tracking, Series 11 gives you a daily sleep score. It’s an easy way to help measure and understand the quality of your sleep, so you can make it more restorative.
- GET HYPERTENSION NOTIFICATIONS—Did you know that Series 11 can spot signs of chronic high blood pressure? By analyzing how your blood vessels respond to beats of the heart, it can notify you of possible hypertension.*
- SAFETY FEATURES—A smartwatch that puts your safety first. Series 11 can detect a hard fall or severe car crash, automatically help connect you with emergency services, and notify your emergency contacts.* Check In can automatically notify a loved one when you’ve arrived at your destination.
- A POWERFUL FITNESS TRACKER—With advanced metrics and motivating features like Pacer, Heart Rate Zones, training load, and Workout Buddy powered by Apple Intelligence from your nearby iPhone*—Series 11 is made to help everyone stay active, from runners and hikers to strength-training enthusiasts.
How to interpret Apple Watch versus Garmin today
The study’s Garmin entry was the Vivosmart HR, not a current Garmin watch. It cannot establish how a newer Garmin compares with a current Apple Watch. Nor does the available evidence support a present-day league table across brands: other records include studies of newer models, but their accessible details do not provide a comparable set of estimates under one shared protocol. A systematic review and records of studies involving Apple Watch 6, Polar Vantage V, Fitbit Sense, Apple Watch Series 4, Garmin Fenix 5, and Fitbit Versa provide broader context, but not a reliable current-model ranking.
Why workout type and fit matter
Intensity and movement
The treadmill study’s decline in wrist-device agreement at faster speeds is a reason to treat workout heart rate as an estimate, especially during harder efforts. It does not show that every wrist reading fails at high intensity, or how the same watches perform outdoors, on a bike, or during strength training.
Rank #3
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- GET SMARTER HEALTH INSIGHTS—Apple Watch SE 3 is an advanced health tracker that helps you better understand your body. The smartwatch sends alerts for an irregular heart rhythm, or an unusually high or low heart rate.* You can view your overnight health tracking metrics with the Vitals app,* track your sleep score, and get sleep apnea notifications.*
- A GREAT FITNESS TRACKER—SE 3 can track your workouts in a healthy number of ways—from running and strength training to simply achieving your 10K steps a day. With real-time metrics and Workout Buddy powered by Apple Intelligence from your nearby iPhone,* you’ll hit your goals like never before.
- KEEP HELP CLOSE AT HAND—SE 3 is a smartwatch that can detect a hard fall or severe car crash and automatically help connect you to emergency services and notify your emergency contacts.* Check In can automatically notify a loved one when you’ve arrived at your destination.
- WOMEN’S HEALTH INSIGHTS—SE 3 has advanced sensors that track your wrist temperature while you sleep. With this smartwatch, you can log your periods and symptoms, get period predictions, and get notified of cycle deviations.*
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Position and contact
Apple recommends a good fit and notes that it may not get a reliable reading every time for every person. It also says occasional measurements can appear abnormally high or low. Garmin recommends wearing its device above the wrist bone, snugly but comfortably, so it does not shift during exercise; its wear guidance says to use a heart-rate monitor strap when accuracy is critical.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What Apple’s current sensor guidance does—and doesn’t—establish
Apple states an optical sensor range of 30–210 beats per minute. That is an operating range, not a guarantee of accuracy throughout it. Apple’s current guidance says Series 12 and Ultra 4 use green LEDs for daytime measurements as often as every five seconds; when a user opens Heart Rate and touches a finger to the Digital Crown, electrical-sensor readings are taken once per second. Those product details describe measurement behavior, not independent comparative validation.
Rank #4
![Apple Watch SE 3 [GPS 40mm] Smartwatch with Midnight Aluminum Case with Midnight Sport Band - S/M. Fitness and Sleep Trackers, Heart Rate Monitor, Always-On Display, Water Resistant](https://m.media-amazon.com/images/I/31Gq8SToFJL._SL160_.jpg)
- GET SMARTER HEALTH INSIGHTS—Apple Watch SE 3 is an advanced health tracker that helps you better understand your body. The smartwatch sends alerts for an irregular heart rhythm, or an unusually high or low heart rate.* You can view your overnight health tracking metrics with the Vitals app,* track your sleep score, and get sleep apnea notifications.*
- A GREAT FITNESS TRACKER—SE 3 can track your workouts in a healthy number of ways—from running and strength training to simply achieving your 10K steps a day. With real-time metrics and Workout Buddy powered by Apple Intelligence from your nearby iPhone,* you’ll hit your goals like never before.
- KEEP HELP CLOSE AT HAND—SE 3 is a smartwatch that can detect a hard fall or severe car crash and automatically help connect you to emergency services and notify your emergency contacts.* Check In can automatically notify a loved one when you’ve arrived at your destination.
- WOMEN’S HEALTH INSIGHTS—SE 3 has advanced sensors that track your wrist temperature while you sleep. With this smartwatch, you can log your periods and symptoms, get period predictions, and get notified of cycle deviations.*
- GREAT BATTERY LIFE AND FASTER CHARGING—Enjoy a smartwatch with all-day, 18-hour battery life* from sunup to sundown. Then charge up to twice as fast as SE 2* and get up to 8 hours of battery in just 15 minutes.*
Apple says Series 4 and later and all Ultra models have electrical heart sensors in the Digital Crown and back. ECG app availability varies by region and is not supported on Apple Watch SE. The electrical sensor and ECG feature should not be confused with ordinary optical workout readings, or treated as proof that those readings are diagnostic.
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When a chest strap may make sense
If workout heart-rate tracking is a priority and you want an alternative to wrist optics, a chest strap is a reasonable option to consider. The comparative result here is specifically for the Polar H7; it does not establish the accuracy of Polar H10 or every strap for every person. Check that any strap works with your watch or training app before buying. Garmin likewise recommends a heart-rate monitor strap when accuracy is critical.
Quick Recap
Practical takeaway
- For ordinary exercise tracking, the 2019 results show Apple Watch III performed strongly among the tested wrist watches, but do not predict the performance of current models.
- For demanding workouts where heart-rate agreement matters most, a chest strap has stronger support in this particular study than wrist devices; its result is model- and protocol-specific.
- If heart rate is needed for a health concern or clinical monitoring, consult a qualified clinician rather than relying on a smartwatch or fitness strap to diagnose or rule out a condition.
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