Key facts
- Wearable optical heart rate sensors use photoplethysmography, an optical method for measuring changes in blood volume under the skin. 1
- Absolute error during activity was on average 30% higher than at rest in a comparison of consumer and research wearables. 1
- A wrist-worn sports watch showed a mean absolute error of 6.41 bpm against a chest strap ECG, an upper-arm sensor 1.43 bpm. 4
- In a systematic review of 10 studies, evidence on skin tone and wrist heart rate accuracy was described as inconclusive. 6
How do wrist sensors and chest straps measure heart rate?
A wrist watch or band usually measures heart rate with light. Bent and colleagues describe photoplethysmography (PPG) as an optical method for measuring changes in blood volume under the skin.1 Koerber and colleagues describe the same principle as analysis of reflected LED light on the skin.6
A chest strap works differently. The strap used as the reference in several studies below, the Polar H10, is an electrocardiogram (ECG) chest strap, which means it picks up the heart’s electrical signal instead of light.45 That is why researchers use it as the yardstick when they test wrist devices.
The two methods have different weak spots. Bent and colleagues name three sources of inaccuracy in optical sensors: diverse skin types, motion artifacts and signal crossover.1 This guide reads what the studies found and shows their limits, because device models change faster than studies get published.
What did the validation studies find?
Wrist heart rate is accurate enough for many uses, but not equally in every situation. The table lists the studies read for this page with the reference each used and what limits it.
| Study | What was compared | Main finding | Limit |
|---|---|---|---|
| Bent 2020, npj Digital Medicine1 | Consumer and research-grade wearables across skin tones, activities and devices | No statistically significant difference in accuracy across skin tones; absolute error during activity about 30% higher than during rest; devices differ. | Compares devices at a given time; models since have changed. |
| Fuller 2020, JMIR mHealth2 | 158 publications on nine commercial brands | Accurate for heart rate in laboratory settings, but it varies by maker and device type; Apple Watch and Garmin most accurate, Fitbit tending toward underestimation. | Studies up to May 2019; the authors say newer models call for newer reviews. |
| Dooley 2017, JMIR mHealth3 | 62 people, three wrist devices against a heart rate chest strap at rest, light, moderate and vigorous treadmill effort | Mean absolute percentage error: Apple Watch 1.14% to 6.70%, Fitbit Charge HR 2.38% to 16.99%, Garmin Forerunner 225 7.87% to 24.38%. | Older devices; one treadmill protocol. |
| Schweizer 2025, JMIR Cardio4 | 16 people, nine activities, Polar Verity Sense and Polar Vantage V2 against a Polar H10 ECG chest strap | Upper arm: mean absolute error 1.43 bpm. Wrist (non-dominant): 6.41 bpm, with accuracy varying by activity. | Small sample of healthy adults; two devices from one brand. |
| Koerber 2023, J Racial Ethn Health Disparities6 | Systematic review of 10 studies (469 people) on skin tone and wrist heart rate | Four studies reported lower accuracy with darker skin, four no effect, two mixed. The authors call the evidence inconclusive. | Small studies; skin tone measured in different ways. |
Percentages and errors are those reported in the abstracts. Study results are group averages, not a promise for your own device.
What does the error look like in beats per minute?
Percentages are hard to feel. A worked example helps. Suppose your true heart rate during a run is 150 beats per minute, measured by a chest strap.
| Device in the study | Reported error | Calculation | Typical error at 150 bpm |
|---|---|---|---|
| Upper-arm optical sensor (Verity Sense)4 | 1.35% mean absolute percentage error | 150 × 0.0135 | About 2 bpm |
| Wrist sports watch (Vantage V2)4 | 6.82% mean absolute percentage error | 150 × 0.0682 | About 10 bpm |
| Apple Watch, upper end of range3 | 6.70% | 150 × 0.067 | About 10 bpm |
| Garmin Forerunner 225, upper end of range3 | 24.38% | 150 × 0.2438 | About 37 bpm |
Arithmetic on the reported percentages. A mean absolute percentage error is an average across measurements, so single readings can be closer or further off. The upper ends come from the hardest conditions in a 2017 study of older devices.
A 10 bpm error can matter if you train by heart rate zones, which the guide to heart rate zones explains. A 2 bpm error is much less likely to change which zone you read. For a resting reading taken while seated, the picture is different. Bent and colleagues concluded that devices are all reasonably accurate at resting and prolonged elevated heart rate, with differences in how they respond to changes in activity.1
When does a chest strap matter?
The findings above point to a few situations in which a strap is the safer choice.
- Interval work and sprints. Optical error rose with movement in the studies, and the 2025 wrist watch did better at high intensity than at low heart rates.14
- Heart rate variability (HRV). The Cleveland Clinic says an EKG is more accurate than a smartwatch and most wrist-worn trackers usually are not sensitive enough to detect HRV accurately.7 In a study of 25 people, the Polar H10 chest strap agreed strongly with an ECG at rest (correlation 0.95).5
- Testing a new device. A strap gives you a reference to compare a watch against.
- Training by tight heart rate targets. A 10 bpm miss can move you between zones.
The chest strap is not flawless either. In the Polar H10 study, linear HRV measures agreed well with ECG, but a non-linear measure called DFA a1 showed wider bias at higher exercise intensities.5 The authors say linear measures can be recommended for practitioners.5
When a wrist or arm sensor is fine
For all-day wear, resting heart rate and sleep trends, the convenience of a band you never take off often outweighs a few beats of error at the top end. Our guide on how to measure resting heart rate shows how to cross-check a resting number by hand. For HRV, see the published guide to the best HRV monitors.
Skin tone, tattoos and motion: the open questions
Optical sensors depend on light reaching blood vessels, so melanin, motion and fit matter in principle.1 The evidence is unsettled. Bent and colleagues found no statistically significant difference in accuracy across skin tones in their own tests.1 Koerber and colleagues reviewed 10 studies with 469 participants: four reported a significant reduction in accuracy in darker-skinned people, four found none and two were mixed.6
Their conclusion is careful. Preliminary evidence is inconclusive, but some studies suggest wearables may be less accurate in participants with darker skin, and larger, better-stratified studies are needed.6 If you have a darker skin tone, a strap is a simple way to check whether your device agrees with a reference.
How to compare your wrist reading with a chest strap at home
- Wear both at once. Wear the watch or band and a chest strap during the same session. Studies compare devices against a strap in just this way.34
- Record three moments. Note both readings while seated at rest, at a steady effort, and during the hardest part of the session, since error was larger during activity.1
- Do it twice. Repeat on another day. Reliability of the wrist watch varied between activities in the 2025 study.4
- Compare the differences. Subtract one reading from the other at each moment. Small differences at rest and steady effort are expected, and a large gap in hard intervals points to the strap as the better reference.
- Decide what the watch is for. Use it for trends if it tracks the strap well at rest and steady effort, and the strap for hard sessions.
Nothing here replaces a clinical check. If you notice a heart rate that seems far off from how you feel, or you have symptoms, talk to a health professional rather than comparing gadgets.
What a wearable measures, and what it does not
A wrist band that reports heart rate measures a pulse signal and estimates beats per minute. It does not record the electrical activity of the heart, it does not diagnose a rhythm problem, and its HRV is an estimate. The Cleveland Clinic says an EKG is more accurate than a smartwatch for HRV.7
Elio’s product page says the band can be worn on the wrist or upper arm.8 Its result for the upper arm should not be inferred from the Polar Verity Sense study above, which tested a different device.4 Elio is a wellness band that shows heart rate and HRV trends in the Chutex app. It is not a chest strap and not a diagnostic device.
Frequently asked questions
Is a chest strap more accurate than a wrist heart rate monitor?
In validation studies a chest strap ECG is the usual reference. In a 2025 study of 16 people, a wrist sports watch had a mean absolute error of 6.41 bpm against it, and an upper-arm sensor 1.43 bpm. Accuracy depends on the device and the activity.
How accurate is wrist heart rate during exercise?
A study that compared a consumer wearable set at different exercise intensities found error varying widely. Apple Watch error ranged from 1.14% to 6.70% and Garmin Forerunner 225 from 7.87% to 24.38%. Those are 2017 models. Optical error was on average 30% higher during activity than at rest in another study.
Why is wrist heart rate less accurate during workouts?
Photoplethysmography reads changes in blood volume with light, and researchers name motion artifacts, skin type and signal crossover as sources of error. Movement is a bigger problem in intervals than in steady effort.
Can a smartwatch measure HRV as well as a chest strap?
The Cleveland Clinic says an EKG is more accurate than a smartwatch and that most wrist-worn trackers usually are not sensitive enough to detect HRV accurately. A chest strap agreed strongly with ECG at rest in a study of 25 people.
Do wrist heart rate monitors work on dark skin?
The evidence is inconclusive. A systematic review of 10 studies found four with lower accuracy in darker skin, four with no effect and two mixed. Another comparison found no statistically significant difference across skin tones.
When should I use a chest strap?
A strap is the safer pick for intervals, for HRV measurements and when you train by tight heart rate targets, because optical error rises with movement. For all-day wear and resting trends, a wrist or arm band is often enough.
Do I need a chest strap for resting heart rate?
Not necessarily. A pooled comparison concluded that devices are all reasonably accurate at resting and prolonged elevated heart rate. You can check a resting number by taking your pulse by hand.
Where can I wear a heart rate sensor besides the wrist?
In the 2025 study, the upper arm gave the lowest error of the positions tested. Elio’s product page says the band can be worn on the wrist or upper arm, but that study tested a different device.
Sources
- Bent B, Goldstein BA, Kibbe WA, Dunn JP. Investigating sources of inaccuracy in wearable optical heart rate sensors. npj Digit Med. 2020;3:18, PubMed. Retrieved October 16, 2026
- Fuller D, Colwell E, Low J, et al. Reliability and validity of commercially available wearable devices for measuring steps, energy expenditure, and heart rate: systematic review. JMIR Mhealth Uhealth. 2020;8(9):e18694, PubMed. Retrieved October 16, 2026
- Dooley EE, Golaszewski NM, Bartholomew JB. Estimating accuracy at exercise intensities: a comparative study of self-monitoring heart rate and physical activity wearable devices. JMIR Mhealth Uhealth. 2017;5(3):e34, PubMed. Retrieved October 16, 2026
- Schweizer T, Gilgen-Ammann R. Wrist-worn and arm-worn wearables for monitoring heart rate during sedentary and light-to-vigorous physical activities: device validation study. JMIR Cardio. 2025;9:e67110, PubMed. Retrieved October 16, 2026
- Schaffarczyk M, Rogers B, Reer R, Gronwald T. Validity of the Polar H10 sensor for heart rate variability analysis during resting state and incremental exercise. Sensors. 2022;22(17):6536, PubMed. Retrieved October 16, 2026
- Koerber D, Khan S, Shamsheri T, Kirubarajan A, Mehta S. Accuracy of heart rate measurement with wrist-worn wearable devices in various skin tones: a systematic review. J Racial Ethn Health Disparities. 2023;10(6):2676-2684, PubMed. Retrieved October 16, 2026
- Cleveland Clinic, Heart Rate Variability (HRV) (date shown on page: 09/02/2026), Cleveland Clinic. Retrieved October 16, 2026
- Chutex Elio US product page, sensors and price, Chutex. Retrieved October 16, 2026