{
  "registry": "KnowYourPrime Evidence Registry",
  "license": {
    "name": "CC BY 4.0",
    "url": "https://creativecommons.org/licenses/by/4.0/",
    "attribution": "Credit KnowYourPrime and link to the finding URL."
  },
  "fields": {
    "devices": "Devices this finding names, including models it says it does not cover. What was actually tested is in scope.applies_to; exclusions are in scope.does_not_cover.",
    "evidence": "Studies by role: anchor (the rating rests on it), conflicting, null_result, supporting.",
    "industry_ties": "Device-maker ties listed in Europe PMC metadata: author_affiliations names makers an author lists as an affiliation, funders names makers listed as funding. stated_ties holds ties a paper states only in its own conflict, funding or acknowledgement text, each read from that statement and worded to say only what it says. Sources are Europe PMC metadata, funding printed in the abstract, and those reviewed statements. An empty list means no tie was found there, not that the study is independent: many papers have no open full text to read. Metadata, not a judgment of the study. checked false means no Europe PMC metadata was available."
  },
  "id": "KYP-ER-0003",
  "version": "1.0",
  "reviewed": "2026-10-24",
  "url": "https://knowyourprime.com/evidence-wearable-hrv-accuracy",
  "title": "Wearable HRV Accuracy Against ECG",
  "question": "Do consumer watches, rings and bands measure heart rate variability (HRV) accurately compared with an ECG reference?",
  "measurement": "Heart rate variability (HRV)",
  "devices": [
    "Oura",
    "WHOOP",
    "Garmin",
    "Polar",
    "Apple Watch"
  ],
  "rating": {
    "label": "Uncertain",
    "code": "uncertain",
    "definition": "Evidence is conflicting, inconsistent, or difficult to interpret.",
    "rule_version": "1.4",
    "rule_reasons": [
      "Systematic-review or meta-analytic evidence affirms the core relationship.",
      "Multiple supporting studies are consistent with the core relationship.",
      "An anchor study is present but its own reported finding does not cleanly affirm this claim, so it does not count toward the Established threshold.",
      "A clean anchor supports this claim, but an unresolved conflicting study contradicts it on the core relationship, so the evidence is treated as in genuine dispute.",
      "Some evidence conflicts on secondary points that do not change the core direction."
    ]
  },
  "conclusion": "It depends on the device and on keeping still. Overnight, Oura rings agreed closely with ECG in one head-to-head study while Garmin and Polar watches did not, and an Apple Watch test found HRV read consistently low. Agreement is good at rest and falls away with movement, so a single verdict for wearables as a category does not hold.",
  "reasoning": [
    "HRV from a wearable is usually calculated from optical pulse timing rather than from the electrical signal an ECG records, and small timing errors matter more for HRV than for heart rate.",
    "Reviews and several device studies affirm good agreement at rest, and the strongest head-to-head study ranked devices clearly. Against that, an Apple Watch Series 9 and Ultra 2 study failed its equivalence test, an Oura study found accurate HRV only after strict data-quality filtering and larger errors in older adults, and other work shows agreement varies by device and degrades with motion. With clean affirming anchors and core-hitting conflicts both present, the rule rates the claim Uncertain."
  ],
  "key_results": [
    {
      "text": "Against ECG over 536 nights in 13 adults, nocturnal HRV concordance was 0.99 for Oura Gen 4 (MAPE 5.96 percent), 0.97 for Oura Gen 3 (7.15 percent), 0.94 for WHOOP 4.0 (8.17 percent), 0.87 for Garmin Fenix 6 (10.52 percent) and 0.82 for Polar Grit X Pro (16.32 percent, SD 24.39).",
      "source": "doi:10.14814/phy2.70527",
      "source_url": "https://doi.org/10.14814/phy2.70527",
      "source_citation": "Dial et al., Physiological Reports, 2025"
    },
    {
      "text": "Apple Watch Series 9 and Ultra 2 underestimated HRV by 8.31 ms on average against a Polar H10 chest strap, with a mean absolute percentage error of 28.88 percent, across 316 measurements in 39 adults, and fell outside a 10 ms equivalence margin; resting heart rate was accurate.",
      "source": "doi:10.3390/s24196220",
      "source_url": "https://doi.org/10.3390/s24196220",
      "source_citation": "O'Grady et al., Sensors, 2024"
    },
    {
      "text": "Oura HRV agreed strongly with ECG in 114 adults once 5-minute segments with under 80 percent valid beats were filtered out and values were averaged over at least 30 minutes; more than half of participants aged 45 and older exceeded 10 percent median error.",
      "source": "doi:10.3390/s24237475",
      "source_url": "https://doi.org/10.3390/s24237475",
      "source_citation": "Liang et al., Sensors, 2024"
    },
    {
      "text": "A systematic review of 18 studies found agreement between wearable and ECG-derived HRV ranged from very good to excellent at rest and declined progressively as exercise intensity rose.",
      "source": "doi:10.2478/folmed-2018-0012",
      "source_url": "https://doi.org/10.2478/folmed-2018-0012",
      "source_citation": "Georgiou et al., Folia Medica, 2019"
    }
  ],
  "scope": {
    "applies_to": "Consumer wrist, ring and band HRV measured overnight or at rest, compared with ECG or a validated chest strap. Device figures apply to the models and firmware tested.",
    "does_not_cover": "HRV during exercise, which agrees less well; devices not named above, including Apple Watch Series 10 and later, Samsung, Fitbit and Ultrahuman, which were not in the head-to-head study; whether HRV predicts any health outcome."
  },
  "limitations": [
    "The head-to-head study that ranks devices had 13 participants, many nights each.",
    "Devices calculate HRV over different windows and at different times of night, so their numbers are not interchangeable even when each is accurate.",
    "Firmware updates can change results after a study is published."
  ],
  "evidence": {
    "anchor": [
      {
        "key": "doi:10.3390/s25185745",
        "title": "A Comparative Study Between ECG- and PPG-Based Heart Rate Sensors for Heart Rate Variability Measurements: Influence of Body Position, Duration, Sex, and Age.",
        "first_author": "Coste",
        "journal": "Sensors (Basel, Switzerland)",
        "year": 2025,
        "url": "https://doi.org/10.3390/s25185745",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1123/ijspp.2025-0126",
        "title": "Limited Validity of the Low-Cost Coospo H808S Heart-Rate Monitor Compared to the Polar H10.",
        "first_author": "Protzen",
        "journal": "International journal of sports physiology and performance",
        "year": 2025,
        "url": "https://doi.org/10.1123/ijspp.2025-0126",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.14814/phy2.70527",
        "title": "Validation of nocturnal resting heart rate and heart rate variability in consumer wearables.",
        "first_author": "Dial",
        "journal": "Physiological reports",
        "year": 2025,
        "url": "https://doi.org/10.14814/phy2.70527",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.3390/s24237475",
        "title": "Deriving Accurate Nocturnal Heart Rate, rMSSD and Frequency HRV from the Oura Ring.",
        "first_author": "Liang",
        "journal": "Sensors (Basel, Switzerland)",
        "year": 2024,
        "url": "https://doi.org/10.3390/s24237475",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1111/psyp.14604",
        "title": "Publication guidelines for human heart rate and heart rate variability studies in psychophysiology-Part 1: Physiological underpinnings and foundations of measurement.",
        "first_author": "Quigley",
        "journal": "Psychophysiology",
        "year": 2024,
        "url": "https://doi.org/10.1111/psyp.14604",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.3390/s24196220",
        "title": "The Validity of Apple Watch Series 9 and Ultra 2 for Serial Measurements of Heart Rate Variability and Resting Heart Rate.",
        "first_author": "O'Grady",
        "journal": "Sensors (Basel, Switzerland)",
        "year": 2024,
        "url": "https://doi.org/10.3390/s24196220",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.2478/folmed-2018-0012",
        "title": "Can Wearable Devices Accurately Measure Heart Rate Variability? A Systematic Review.",
        "first_author": "Georgiou",
        "journal": "Folia medica",
        "year": 2019,
        "url": "https://doi.org/10.2478/folmed-2018-0012",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      }
    ],
    "conflicting": [
      {
        "key": "doi:10.1186/s12872-026-06556-4",
        "title": "Reliability and inter-device agreement of multi-site heart rate variability measurements during transcutaneous auricular vagus nerve stimulation: a prospective single-arm methodological physiological study.",
        "first_author": "Hatik",
        "journal": "BMC cardiovascular disorders",
        "year": 2026,
        "url": "https://doi.org/10.1186/s12872-026-06556-4",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.3390/s25247556",
        "title": "Signal Quality Assessment and Reconstruction of PPG-Derived Signals for Heart Rate and Variability Estimation in In-Vehicle Applications: A Comparative Review and Empirical Validation.",
        "first_author": "Gao",
        "journal": "Sensors (Basel, Switzerland)",
        "year": 2025,
        "url": "https://doi.org/10.3390/s25247556",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1016/j.ijcard.2004.09.013",
        "title": "The reliability of short-term measurements of heart rate variability.",
        "first_author": "Sandercock",
        "journal": "International journal of cardiology",
        "year": 2005,
        "url": "https://doi.org/10.1016/j.ijcard.2004.09.013",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      }
    ],
    "supporting": [
      {
        "key": "doi:10.3390/s26165192",
        "title": "Accuracy of Photoplethysmography-Derived Pulse Rate Variability Compared with Electrocardiography-Derived Heart Rate Variability: A Systematic Review and Meta-Analysis.",
        "first_author": "Xu",
        "journal": "Sensors (Basel, Switzerland)",
        "year": 2026,
        "url": "https://doi.org/10.3390/s26165192",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1088/1361-6579/ae95ae",
        "title": "Evaluation of HRV-PRV agreement with autoencoder-based signal quality assessment in resting and dynamic conditions.",
        "first_author": "Olszewski",
        "journal": "Physiological measurement",
        "year": 2026,
        "url": "https://doi.org/10.1088/1361-6579/ae95ae",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1088/1361-6579/ae66c7",
        "title": "Reliability of resting-state photoplethysmogram-based pulse rate variability in lifespan samples: implications for cardiovascular research.",
        "first_author": "Han",
        "journal": "Physiological measurement",
        "year": 2026,
        "url": "https://doi.org/10.1088/1361-6579/ae66c7",
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        }
      },
      {
        "key": "doi:10.1016/j.ijpsycho.2026.113341",
        "title": "Test-retest reliability of time- and frequency-domain measures of short-term resting heart rate variability in a healthy young population.",
        "first_author": "North",
        "journal": "International journal of psychophysiology : official journal of the International Organization of Psychophysiology",
        "year": 2026,
        "url": "https://doi.org/10.1016/j.ijpsycho.2026.113341",
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        "key": "doi:10.1038/s41598-026-55797-y",
        "title": "Validation of the ultra short term heart rate variability measures under changing psychophysiological state of the healthy participants at rest.",
        "first_author": "Maciejewska",
        "journal": "Scientific reports",
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        "url": "https://doi.org/10.1038/s41598-026-55797-y",
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        }
      },
      {
        "key": "doi:10.3390/s25227091",
        "title": "Butterworth Filtering at 500 Hz Optimizes PPG-Based Heart Rate Variability Analysis for Wearable Devices: A Comparative Study.",
        "first_author": "Abdrasulova",
        "journal": "Sensors (Basel, Switzerland)",
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      {
        "key": "doi:10.1007/s00380-024-02506-2",
        "title": "Comparative analysis of heart rate variability indices from ballistocardiogram and electrocardiogram: a study on measurement agreement.",
        "first_author": "Yanagisawa",
        "journal": "Heart and vessels",
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        "title": "Effects of electrocardiographic noise on ultra-short term Heart Rate Variability indices.",
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        "title": "Hybrid CNN-LSTM Model for Evaluating Heart Rate Variability from Pulse-to-Pulse Intervals.",
        "first_author": "Sharma",
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        "title": "The Novel Estimation Algorithm of Heart Rate Variability and Stress Using Facial Video Analysis.",
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        "title": "Validity of Heart Rate Variability Measured with Apple Watch Series 6 Compared to Laboratory Measures.",
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        "title": "Optimizing Intersession Reliability of Heart Rate Variability-The Effects of Artifact Correction and Breathing Type.",
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        "journal": "Journal of strength and conditioning research",
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      },
      {
        "key": "doi:10.3390/s21030902",
        "title": "Validity of the Polar H7 Heart Rate Sensor for Heart Rate Variability Analysis during Exercise in Different Age, Body Composition and Fitness Level Groups.",
        "first_author": "Hernández-Vicente",
        "journal": "Sensors (Basel, Switzerland)",
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        "url": "https://doi.org/10.3390/s21030902",
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        "key": "doi:10.1109/embc.2018.8513551",
        "title": "Heart Rate Variability Analysis on CEBS Database Signals.",
        "first_author": "Siecinski",
        "journal": "Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference",
        "year": 2019,
        "url": "https://doi.org/10.1109/EMBC.2018.8513551",
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      },
      {
        "key": "doi:10.1016/j.hrthm.2016.02.006",
        "title": "Reference values for time- and frequency-domain heart rate variability measures.",
        "first_author": "Sammito",
        "journal": "Heart rhythm",
        "year": 2018,
        "url": "https://doi.org/10.1016/j.hrthm.2016.02.006",
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        }
      },
      {
        "key": "doi:10.1007/s10286-017-0445-3",
        "title": "Reproducibility of 24-h heart rate variability in children.",
        "first_author": "Bjelakovic",
        "journal": "Clinical autonomic research : official journal of the Clinical Autonomic Research Society",
        "year": 2018,
        "url": "https://doi.org/10.1007/s10286-017-0445-3",
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        }
      },
      {
        "key": "doi:10.1016/j.cmpb.2013.07.024",
        "title": "Kubios HRV--heart rate variability analysis software.",
        "first_author": "Tarvainen",
        "journal": "Computer methods and programs in biomedicine",
        "year": 2014,
        "url": "https://doi.org/10.1016/j.cmpb.2013.07.024",
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      },
      {
        "key": "doi:10.1080/02640414.2012.721931",
        "title": "Intra-day and inter-day reliability of heart rate variability measurement.",
        "first_author": "Cipryan",
        "journal": "Journal of sports sciences",
        "year": 2013,
        "url": "https://doi.org/10.1080/02640414.2012.721931",
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        }
      },
      {
        "key": "doi:10.1111/j.1540-8159.2010.02841.x",
        "title": "A quantitative systematic review of normal values for short-term heart rate variability in healthy adults.",
        "first_author": "Nunan",
        "journal": "Pacing and clinical electrophysiology : PACE",
        "year": 2011,
        "url": "https://doi.org/10.1111/j.1540-8159.2010.02841.x",
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        }
      },
      {
        "key": "doi:10.1249/mss.0b013e318184a4b1",
        "title": "Validity and reliability of short-term heart-rate variability from the Polar S810.",
        "first_author": "Nunan",
        "journal": "Medicine and science in sports and exercise",
        "year": 2009,
        "url": "https://doi.org/10.1249/MSS.0b013e318184a4b1",
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      }
    ]
  },
  "evidence_last_evaluated": "Oct 24, 2026",
  "rating_history": [
    {
      "date": "2026-07-09",
      "rating": "Uncertain",
      "from": null,
      "rule_version": "1.4"
    }
  ],
  "versions": [
    {
      "version": "1.0",
      "date": "2026-10-24",
      "rating": "Uncertain",
      "change": "First published."
    }
  ],
  "research_desk": "https://knowyourprime.com/research-desk-hrv#measurement-validity",
  "related_findings": [
    "https://knowyourprime.com/evidence-chest-strap-hrv-accuracy",
    "https://knowyourprime.com/evidence-readiness-recovery-score-validity"
  ],
  "related_articles": [
    "https://knowyourprime.com/how-accurate-is-ppg-hrv-vs-ecg-hrv",
    "https://knowyourprime.com/apple-watch-hrv-resting-heart-rate-accuracy",
    "https://knowyourprime.com/chest-strap-hrv-accuracy-vs-ecg"
  ],
  "methodology": "https://knowyourprime.com/methodology",
  "citation": "KnowYourPrime Evidence Registry, Finding KYP-ER-0003, version 1.0, reviewed 2026-10-24. https://knowyourprime.com/evidence-wearable-hrv-accuracy"
}