Device comparisons
Polar vs Garmin: Overnight Heart Rate Accuracy from a Published Study
In Miller et al. (2022, 53 adults), Polar Vantage V tracked overnight heart rate more closely than Garmin Forerunner 245 (ICC 0.93 vs 0.41). Sleep staging was similar. Those are older models than the watches named here.
Published study results
| Metric | Polar (Vantage V3 / Grit X2 Pro) | Garmin (Forerunner 965 / Fenix 8) |
|---|---|---|
| Overnight heart rateICC vs ECGMiller et al. 2022, n=53 | 0.93Polar Vantage VCloser in this study | 0.41Forerunner 245 |
| Sleep stagesEpoch agreement vs PSGMiller et al. 2022, n=53 | 51%κ 0.28 · Vantage V | 50%κ 0.25 · Forerunner 245 |
Each row is one statistic from a study already cited on this page. The link names the sample size when this page already states it. This is not a new measurement.
Devices
Polar (Vantage V3 / Grit X2 Pro)
Sports watchDevice guideGarmin (Forerunner 965 / Fenix 8)
Sports watchDevice guidePolar Vantage V3 in night black: product photograph from Polar. Garmin fēnix 8 47 mm AMOLED, slate gray case with a black silicone band (part 010-02904-00): product photograph from Garmin.
At a glance
Miller et al. 2022 tested six devices, including Polar Vantage V and Garmin Forerunner 245, on 53 adults for one night. Vantage V3 and Forerunner 965 were not in that study.
| Specification | Polar (Vantage V3 / Grit X2 Pro) | Garmin (Forerunner 965 / Fenix 8) |
|---|---|---|
| Overnight heart rateICC vs ECG | 0.93Polar Vantage VCloser in this study | 0.41Forerunner 245 |
| Sleep stagesEpoch agreement vs PSGNear tie | 51%κ 0.28 · Vantage V | 50%κ 0.25 · Forerunner 245 |
Primary rows only. The study tables further down list more results from the accuracy database.
Hardware specs
| Specification | Polar (Vantage V3 / Grit X2 Pro) | Garmin (Forerunner 965 / Fenix 8) |
|---|---|---|
| Battery LifeDiffers | 11 days smartwatch (V3 and Grit X2 Pro) | Up to 23 days (FR965); up to 16 days (Fenix 8 47 mm AMOLED) |
| Training batteryDiffers | Up to 42 h (V3) / 40 h (Grit X2 Pro) | — |
| Water ResistanceDiffers | WR50 (V3); WR100 (Grit X2 Pro) | 5 ATM (FR965); 10 ATM + 40 m dive (Fenix 8) |
Hardware only. Study results are not repeated in this table. Differs marks values that are not the same. An em dash means this page did not publish that figure.
Specs verified on October 17, 2026: Miller et al. 2022, Sensors (six devices vs PSG and ECG, n=53), Nuuttila et al. 2021, Sensors (Polar Vantage V2), Polar Vantage V3 user manual: technical specifications, Polar Grit X2 Pro user manual: technical specifications, Polar H10 user manual (Bluetooth and ANT+), Polar: Nightly Recharge, Garmin Forerunner 965 owner's manual: battery information, Garmin Forerunner 965 owner's manual: specifications, Garmin Fenix 8 owner's manual: battery information, Garmin Fenix 8 owner's manual: specifications, Garmin: Understanding HRV Status.
Pros and cons
Polar (Vantage V3 / Grit X2 Pro)
Pros
- Overnight HR ICC 0.93 vs ECG for Vantage V (Miller 2022)
- Vantage V2 nocturnal HR ICC 0.998 vs chest strap (Nuuttila 2021)
- Nightly Recharge recovery measurement
Cons
- 11 days smartwatch battery, shorter than Forerunner 965's 23 days
- Sleep-stage agreement 51% (κ 0.28) for Vantage V (Miller 2022)
Garmin (Forerunner 965 / Fenix 8)
Pros
- Up to 23 days smartwatch battery (FR965); up to 16 days (Fenix 8 47 mm AMOLED)
- HRV Status against a 3-week baseline
- Fenix 8: 10 ATM plus 40 m dive rating
Cons
- Forerunner 245 overnight HR ICC 0.41 vs ECG (Miller 2022)
- Sleep-stage agreement 50% (κ 0.25) for FR245 (Miller 2022)
What published studies show
One table per metric. These rows come from the accuracy database and are not repeated as a second card list. From the wearable accuracy database (v1.0.0).
Heart rate at rest1 study
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Vivoactive 4 | ρc = 0.9998Lin's concordance correlation | ECG | n = 263, 30-min standardised recording | Theurl et al. (2023)Independent |
Heart rate during exercise8 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Polar Ignite 3mixed rest/stress/walking | 9–14 bpm (group range)Mean absolute error | ECG chest strap (Zephyr BioHarness / | n = 45, Rest, cognitive stress, steady and intermittent walking in neutral/ | Gielen et al. (2026)Funding not reported |
| Polar Pacermixed rest/stress/walking | 9–14 bpm (group range)Mean absolute error | ECG chest strap (Zephyr BioHarness / | n = 45, Rest, cognitive stress, steady and intermittent walking in neutral/ | Gielen et al. (2026)Funding not reported |
| Polar Verity Sense | Strongest agreement (with WHOOP upper arm) in graded treadmillStudy finding (no single number) | ECG chest strap (Polar H7/ | n = 28, Rest, warm-up, burpees, Bruce treadmill | Moghaddam et al. (2025)Funding not reported |
| Polar Verity Sense | Significantly lower MAE than Polar Pacer Pro and Galaxy Watch 6Study finding (no single number) | ECG chest strap (Polar H7/ | n = 37, Low/ | Jeong et al. (2026)Independent |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Polar Pacer Pro | Significantly higher MAE than Apple Watch SE and Verity SenseStudy finding (no single number) | ECG chest strap (Polar H7/ | n = 37, Low/ | Jeong et al. (2026)Independent |
| Polar Vantage V | 2.2%–6.7% (range by intensity)Coefficient of variation | ECG chest strap (Polar H7/ | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
6 more results in the database. Heart rate accuracy across devices →
Overnight heart rate3 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Polar Grit X Pro | 2.71%Mean absolute percentage error | ECG | n = 13, Home, during sleep, 536 nights | Dial et al. (2025)Independent |
| Polar Grit X Pro | 0.86Lin's concordance correlation | ECG | n = 13, Home, during sleep, 536 nights | Dial et al. (2025)Independent |
| Polar Vantage V | ICC 0.93Intraclass correlation | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
| Polar Vantage V | 1.5 bpm (absolute bias)Mean absolute error | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Polar Vantage V2 | ICC 0.998Intraclass correlation | ECG chest strap (Polar H7/ | n = 29, Supine lab (5 min) and home sleep (4 h) | Nuuttila et al. (2021)Maker funded |
| Garmin Forerunner 245 Music | ICC 0.41Intraclass correlation | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
1 more result in the database. Heart rate accuracy across devices →
HRV (RMSSD)4 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Polar Grit X Pro | 16.32%Mean absolute percentage error | ECG | n = 13, Home, during sleep, 536 nights | Dial et al. (2025)Independent |
| Polar Grit X Pro | 0.82Lin's concordance correlation | ECG | n = 13, Home, during sleep, 536 nights | Dial et al. (2025)Independent |
| Polar Vantage V | ICC 0.65Intraclass correlation | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
| Polar Vantage V | 18.8 ms (absolute bias)Mean absolute error (absolute bias) | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Polar Vantage V2 | ICC 0.931 (nocturnal LnRMSSD)Intraclass correlation | ECG chest strap (Polar H7/ | n = 29, Supine lab (5 min) and home sleep (4 h) | Nuuttila et al. (2021)Maker funded |
| Garmin Fenix 6 | 10.52%Mean absolute percentage error | ECG | n = 13, Home, during sleep, 536 nights | Dial et al. (2025)Independent |
4 more results in the database. HRV accuracy across devices →
Sleep stages (4-stage)2 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Polar Vantage V | 51%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
| Polar Vantage V | κ = 0.28Cohen's kappa | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
| Garmin Forerunner 245 Music | 50%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
| Garmin Forerunner 245 Music | κ = 0.25Cohen's kappa | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
More results (1)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Vivosmart 4 | κ = 0.21Cohen's kappa | Polysomnography (PSG) | n = 25, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
Sleep vs wake (2-stage)3 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Polar Vantage V | 87%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
| Polar Vantage V | κ = 0.44Cohen's kappa | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
| Garmin Vivosmart 4 | > 90% (all devices)Sensitivity | Polysomnography (PSG) | n = 62, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
| Garmin Fenix 5S | Worse than actigraphyStudy finding (no single number) | Polysomnography (PSG) | n = 34, Sleep laboratory, 3 nights incl. disrupted night | Chinoy et al. (2021)Funding not reported |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Vivosmart 3 | Worse than actigraphyStudy finding (no single number) | Polysomnography (PSG) | n = 34, Sleep laboratory, 3 nights incl. disrupted night | Chinoy et al. (2021)Funding not reported |
| Garmin Forerunner 245 Music | 89%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
1 more result in the database. Sleep accuracy across devices →
Total sleep time1 study
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Polar Ignite | MAE 45.08 min (overestimate)Mean absolute error | Polysomnography (PSG) | n = 49, 1 night PSG + MSLT | Budig et al. (2022)Independent |
| Garmin Forerunner 945 | MAE 84.63 min (overestimate)Mean absolute error | Polysomnography (PSG) | n = 49, 1 night PSG + MSLT | Budig et al. (2022)Independent |
Blood oxygen (SpO2)5 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Vivosmart 4 | 3.3% (rest)Root-mean-square error | Medical-grade pulse oximeter | n = 36, Rest, COPD outpatients | Støve et al. (2023)Funding not reported |
| Garmin Venu 2S | 5.8% (RMSE 6.7%)Mean absolute error | Medical-grade pulse oximeter | n = 49, Spot readings, with and without chronic pulmonary disease | Jiang et al. (2023)Independent |
| Garmin Venu 2S | 6.7%Root-mean-square error | Medical-grade pulse oximeter | n = 49, Spot readings, with and without chronic pulmonary disease | Jiang et al. (2023)Independent |
| Garmin Fenix 5X Plus | 9.77% (ICC 0.549)Mean absolute percentage error | Arterial blood gas (SaO2) | n = 13, High altitude 4559 m | Schiefer et al. (2021)Independent |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Fenix 5X Plus | +3.3% at 12,000 ft (LoA −1.9 to 8.6%)Mean bias (signed) | Medical-grade pulse oximeter | n = 23, Normobaric hypoxia, rest, 900–12,000 ft | Lauterbach et al. (2021)Funding not reported |
| Garmin Fenix 6 | 4.29% (CCC 0.10)Mean absolute percentage error | Medical-grade pulse oximeter | n = 22, Normoxic and hypoxic conditions | Carrier et al. (2025)Independent |
VO2max estimate3 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Forerunner 245 | 7.9% / 7.2% (two runs)Mean absolute percentage error | Indirect calorimetry | n = 35, Treadmill ramp test | Engel et al. (2026)Funding not reported |
| Garmin Fenix 6 | 7.05% (CCC 0.73)Mean absolute percentage error | Indirect calorimetry | n = 19, Graded exercise test and outdoor run | Carrier et al. (2025)Independent |
| Garmin Forerunner 920XT | 7.3%Mean absolute percentage error | Indirect calorimetry | n = 24, Lab | Passler et al. (2019)Independent |
Energy expenditure (calories)5 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Polar Vantagetotal energy expenditure | r = 0.69Pearson correlation | Actiheart / | n = 21, Free-living, up to 7 days | Henriksen et al. (2022)Independent |
| Polar Vantage V | 16.3%–28.0% (range by intensity)Coefficient of variation | Indirect calorimetry | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
| Polar Vantage V | 16.54–25.78% (poor in all activities)Coefficient of variation | Indirect calorimetry | n = 60, Sitting, walking, running, resistance, cycling | Hajj-Boutros et al. (2023)Funding not reported |
| Garmin Fenix 5 | 15.9%–34.5% (range by intensity)Coefficient of variation | Indirect calorimetry | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Forerunner 955physical activity energy expenditure, 10 min | +68.61 kcalMean bias (signed) | Indirect calorimetry | n = 51, 10-min recumbent cycling intervals | Kostrna et al. (2026)Independent |
| Garmin Fenix 6walking | 32.0% walk / 21.8% runMean absolute percentage error | Indirect calorimetry | n = 20, Outdoor 2-km walk (6 km/ | Le et al. (2022)Independent |
Verdict
Polar showed closer overnight heart-rate agreement in the one study that tested both brands; Garmin offers longer battery on the Forerunner 965. Sleep staging was similar. The study used older models (Vantage V, Forerunner 245).
Frequently asked questions
Is Polar H10 chest strap compatible with Garmin watches?
Yes. Polar's H10 manual lists Bluetooth and ANT+ heart-rate transmission, which Garmin watches can pair with as an external sensor.
Is Polar or Garmin more accurate overnight?
In Miller et al. (2022), overnight heart rate ICC vs ECG was 0.93 for Polar Vantage V and 0.41 for Garmin Forerunner 245; HRV ICC was 0.65 for Polar (Garmin's HRV came from a 3-minute awake test, so it is not comparable).
Which has longer battery life?
Garmin quotes up to 23 days in smartwatch mode for the Forerunner 965; Polar quotes 11 days for both the Vantage V3 and Grit X2 Pro.
Device research records
Datasets, papers and validation results for the models named on this page.