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Apple Watch performed best among the wrist devices in a 2019 treadmill study, but a Polar chest strap agreed more closely with ECG. The important qualification: the study tested older models, and all wrist devices became less dependable as running intensity rose. It is evidence about those devices under that protocol—not a ranking of current watches.
What “accuracy” means in a heart-rate comparison
A wrist watch estimates pulse using photoplethysmography (PPG): light enters the skin and light-sensitive sensors detect changes in blood volume. Apple says its optical sensor uses green LEDs and photodiodes, and may also use infrared light depending on the model, activity and sleep. A chest strap such as the Polar H7 instead senses electrical activity through electrodes. In the study below, researchers compared both types with a three-lead ECG reference.
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Agreement with ECG is not the same as a percentage score, and it does not establish accuracy for calories, sleep tracking, an ECG feature, or medical diagnosis. The 2019 study reported Lin’s concordance correlation coefficient, a measure of how closely readings agreed with the reference.
What the treadmill study found
A Cleveland Clinic research team studied 50 healthy athletic adults in a prospective treadmill protocol published in 2019. Participants were runners able to complete the protocol; people with certain health conditions and wrist tattoos were excluded. That sample 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 | Sensor type | Concordance with ECG |
|---|---|---|
| Polar H7 | Chest strap | 0.98 |
| Apple Watch III | Wrist optical sensor | 0.96 |
| Fitbit Ionic | Wrist optical sensor | 0.89 |
| Garmin Vivosmart HR | Wrist optical sensor | 0.89 |
| TomTom Spark 3 | Wrist optical sensor | 0.89 |
These figures are concordance coefficients, not “98% accurate” or “96% accurate” ratings. The Polar H7 was closest to ECG overall in this set; Apple Watch III had the highest agreement among the tested watches.
Higher effort widened the gap
At rest, all devices had concordance of at least 0.85. As treadmill speed increased, wrist-device agreement declined. At 8 and 9 mph, none of the wrist watches reached 0.70 concordance. Apple Watch still had the highest agreement among the watches at each tested condition, but that does not mean its readings were consistently close at the hardest stages.
Limits of the comparison
The protocol used indoor treadmill running and short stages. Participants held the handrail while readings were recorded, and the authors did not directly test statistical differences between brands. Outdoor running, different arm movement, other sports, different fit, and different people may produce different results. Most importantly, Apple Watch III, Fitbit Ionic, Garmin Vivosmart HR and TomTom Spark 3 are older models; the findings cannot establish a current-generation winner. The authors’ conclusion that a chest strap or Apple Watch III may be the best choice for imperative accuracy applies to that study’s devices and protocol.
Rank #2
![Apple Watch Series 11 [GPS 42mm] Smartwatch with Rose Gold Aluminum Case with Light Blush Sport Band - S/M. Sleep Score, Fitness Tracker, Health Monitoring, Always-On Display, Water Resistant](https://m.media-amazon.com/images/I/31caPPnRysL._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.
How current Apple Watch guidance fits in
Apple lists a 30–210 beats-per-minute operating range for the optical heart-rate sensor. That is a stated sensor range, not a promise of accuracy throughout it. Apple’s current support 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 places a finger on the Digital Crown, the electrical sensor can provide a reading once per second. These are product descriptions, not independent comparisons with ECG.
Apple says Series 4 and later, along with 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. An electrical reading or ECG feature should not be confused with ordinary optical workout tracking, nor treated as proof that workout readings are diagnostic. Apple cautions: “Even under ideal conditions, Apple Watch may not be able to get a reliable heart rate reading every time for everybody.” Occasional unusually high or low readings can occur.
Why fit and activity matter
An optical sensor needs stable contact with the skin. Apple recommends starting with a good fit; a loose or shifting watch can make measurement more difficult. Garmin’s guidance is to wear a device snugly but comfortably above the wrist bone so it does not move during running or exercise. Garmin recommends a heart-rate monitor strap when accuracy is critical.
Rank #3
![Apple Watch SE 3 [GPS 40mm] Smartwatch with Starlight Aluminum Case with Starlight Sport Band - S/M. Fitness and Sleep Trackers, Heart Rate Monitor, Always-On Display, Water Resistant](https://m.media-amazon.com/images/I/31YiTby0pOL._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.*
- For steady exercise: A well-fitted wrist watch can be convenient for tracking trends, but individual readings may vary.
- For fast intervals or high exertion: The treadmill study found poorer wrist-device agreement as speed rose. A chest strap is a reasonable option when close workout tracking matters.
- For a comparison across devices: Match the activity, intensity, placement, device generation and reference method. A result from indoor treadmill running should not be generalized to cycling, strength training or every outdoor run.
How to choose between Apple Watch and a strap
Choose wrist tracking for convenience and everyday context
Apple Watch provides continuous wear and heart-rate features in one device. If you use it for exercise, fit it securely and interpret a single surprising reading in context rather than assuming it is exact. The available evidence here supports Apple Watch III as a strong performer among the older wrist watches tested, not a claim that a current Apple Watch outperforms current rivals.
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The study’s Polar H7 achieved the closest ECG agreement among the devices tested. That result is specific to the H7 and does not establish the performance of Polar H10 or any other current strap. Check that a strap works with the watch, phone or training app you plan to use; compatibility and setup can vary.
Do not treat a wearable as a clinical monitor
These comparisons concern consumer heart-rate measurements during exercise, not diagnosis or exclusion of a health condition. If symptoms or a need for clinical monitoring are involved, speak with a qualified clinician instead of relying on a smartwatch or fitness strap.
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.*
What can and cannot be concluded about current rivals
Later research has examined combinations such as Apple Watch 6, Polar Vantage V and Fitbit Sense, and Apple Watch Series 4, Garmin Fenix 5, Polar Vantage V and Fitbit Versa. The available published material establishes that these comparisons exist, but does not support reproducing detailed estimates or a current product ranking here. A living systematic review likewise does not turn differing study protocols and device generations into one universal league table.
So, if the question is “How accurate is Apple Watch heart rate compared with Garmin?”, the direct answer is conditional: one 2019 study found Apple Watch III had stronger ECG agreement than Garmin Vivosmart HR under its treadmill conditions, while the Polar H7 chest strap scored higher than either. That is not evidence about today’s Apple Watch and Garmin models under matched testing.
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