Pilot study assessing the influence of skin type on the heart rate measurements obtained by photoplethysmography with the Apple Watch
Open accessAbstract
Photoplethysmographic imaging (PPG) is currently used to measure heart rate (HR) and the accuracy of PPG can be influenced by pigmentation of the skin; however, the effects of skin color-related artifacts on PPG during exercise remain unclear. This study aimed to assess the agreement between the Apple Watch photoplethysmography sensor and a criterion, for measuring heart rate across a range of intensities during exercise and to determine the influence of skin type on the accuracy of the measure. Forty-five males (20-43 y) completed the Fitzpatrick Skin Scale and were classified into three different skin type groups: a) types II (n = 15), III (n = 15) and IV (n = 15). Participants performed a graded incremental cycle-ergometer test while simultaneously wearing the Apple Watch and a Polar monitor as a criterion measure. Data from both devices were collected in 5-s epochs. Correlations between devices were very good (0.96-0.99 [95%CI: 0.94 to 0.99]). Significant differences were observed between skin types II and III when the intensity of the exercise was increased, albeit with trivial to small effect sizes (ES: 0.05 to 0.28). All significant differences corresponded to <2% of relative difference between both devices. Bland-Altman analyses showed a trivial but systematic underestimation of HR in the Apple Watch compared to Polar for all skin types during exercise. In conclusion, the Apple Watch accurately measures HR when cycling at different intensities and certain types of skin seem not to influence these measures, which may have important implications for controlling the intensity of exercise.
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Reduced accuracy in darker skin tones has been linked to missed detection of atrial fibrillation when irregular pulse notifications fail to capture abnormal rhythms.
“Reduced accuracy in darker skin tones has been linked to missed detection of atrial fibrillation when irregular pulse notifications fail to capture abnormal rhythms.”
From Photoplethysmography in Diverse Skin Tones: Evaluating Bias in Smartwatch Health Monitoring (2025) · cites this paper as [7]
The Results and Discussion (pages unavailable) report no significant Apple Watch heart-rate difference for the darkest skin type studied, type IV; the observed differences were in types II and III. The paper assesses heart-rate measurement during cycling, not atrial-fibrillation detection or irregular-pulse notifications. (LLM, conf=0.84)
Checked by a reasoning model — may be wrong.
Experimental — accuracy not yet measuredFor light skin pigmentation, pulse rate mean bias was -1.24 bpm (95% CI -5.31 to 2.83).
“Mean biases were –1.24 (95% CI –5.31 to 2.83) bpm, –0.89 (95% CI –3.70 to 1.93) bpm, and –0.57 (95% CI –9.44 to 8.29) bpm for the corresponding groups (Table 4 and Figures 5-7 [41,60-62]).”
From Impact of skin pigmentation on pulse oximetry blood oxygenation and wearable pulse rate accuracy: systematic review and meta-analysis (2024) · cites this paper as [61]
The Results section (page not available) reports a mean bias of −2 bpm for the lightest skin group studied (type II), with 95% limits of agreement of −8 to 5 bpm. It does not report a bias of −1.24 bpm or a 95% confidence interval of −5.31 to 2.83 bpm; the reported interval is also a different measure. (LLM, conf=0.88)
Checked by a reasoning model — may be wrong.
Experimental — accuracy not yet measuredFor dark skin pigmentation, pulse rate mean bias was -0.57 bpm (95% CI -9.44 to 8.29).
“Mean biases were –1.24 (95% CI –5.31 to 2.83) bpm, –0.89 (95% CI –3.70 to 1.93) bpm, and –0.57 (95% CI –9.44 to 8.29) bpm for the corresponding groups (Table 4 and Figures 5-7 [41,60-62]).”
From Impact of skin pigmentation on pulse oximetry blood oxygenation and wearable pulse rate accuracy: systematic review and meta-analysis (2024) · cites this paper as [61]
The Results section (page unavailable) reports a mean bias of −1 bpm for the darkest skin type studied (type IV), with 95% limits of agreement of −6 to 4 bpm. It does not report the claimed −0.57 bpm or a 95% confidence interval of −9.44 to 8.29 bpm; the reported limits of agreement are a different measure from a confidence interval. (LLM, conf=0.88)
Checked by a reasoning model — may be wrong.
Experimental — accuracy not yet measuredFor medium skin pigmentation, pulse rate 95% limits of agreement were -18.62 to 16.84 bpm.
“Our analysis revealed 95% LoA of –16.02 to 13.54 bpm, –18.62 to 16.84 bpm, and –33.69 to 32.54 bpm for light, medium, and dark skin pigmentation groups, respectively.”
From Impact of skin pigmentation on pulse oximetry blood oxygenation and wearable pulse rate accuracy: systematic review and meta-analysis (2024) · cites this paper as [61]
The Results section reports 95% limits of agreement of −8 to 4 beats/min for skin type III during exercise, not −18.62 to 16.84 bpm. It reports −5 to 5 beats/min for type III at rest. Our copy does not provide a page number for this passage. (LLM, conf=0.89)
Checked by a reasoning model — may be wrong.
Experimental — accuracy not yet measuredFor dark skin pigmentation, pulse rate 95% limits of agreement were -33.69 to 32.54 bpm.
“Our analysis revealed 95% LoA of –16.02 to 13.54 bpm, –18.62 to 16.84 bpm, and –33.69 to 32.54 bpm for light, medium, and dark skin pigmentation groups, respectively.”
From Impact of skin pigmentation on pulse oximetry blood oxygenation and wearable pulse rate accuracy: systematic review and meta-analysis (2024) · cites this paper as [61]
The Results (section 3; page unavailable) report 95% limits of agreement of −6 to 4 bpm for the darkest skin type studied (type IV) during exercise, and −5 to 4 bpm at rest—not −33.69 to 32.54 bpm. The paper also did not include participants with Fitzpatrick skin types V or VI. (LLM, conf=0.90)
Checked by a reasoning model — may be wrong.
Experimental — accuracy not yet measured
For medium skin pigmentation, pulse rate mean bias was -0.89 bpm (95% CI -3.70 to 1.93).
“Mean biases were –1.24 (95% CI –5.31 to 2.83) bpm, –0.89 (95% CI –3.70 to 1.93) bpm, and –0.57 (95% CI –9.44 to 8.29) bpm for the corresponding groups (Table 4 and Figures 5-7 [41,60-62]).”
From Impact of skin pigmentation on pulse oximetry blood oxygenation and wearable pulse rate accuracy: systematic review and meta-analysis (2024) · cites this paper as [61]
The Results (page unavailable) report a mean bias of −2 bpm for skin type III during exercise, with 95% limits of agreement of −8 to 4 bpm; at rest, the reported bias is 0 bpm. The cited paper does not report the claimed −0.89 bpm bias or its stated 95% confidence interval for this group. (LLM, conf=0.84)
Checked by a reasoning model — may be wrong.
Experimental — accuracy not yet measuredFor light skin pigmentation, pulse rate 95% limits of agreement were -16.02 to 13.54 bpm.
“Our analysis revealed 95% LoA of –16.02 to 13.54 bpm, –18.62 to 16.84 bpm, and –33.69 to 32.54 bpm for light, medium, and dark skin pigmentation groups, respectively.”
From Impact of skin pigmentation on pulse oximetry blood oxygenation and wearable pulse rate accuracy: systematic review and meta-analysis (2024) · cites this paper as [61]
The Results section (page not available in our copy) reports 95% limits of agreement of −8 to 5 bpm during exercise for Fitzpatrick type II, the lightest skin group studied, rather than −16.02 to 13.54 bpm. Its reported resting limits for type II are −5 to 4 bpm. (LLM, conf=0.88)
Checked by a reasoning model — may be wrong.
Experimental — accuracy not yet measuredApple Watch devices showed less than 5 bpm variation across skin tones.
“In contrast, Apple Watch devices were more consistent, with <5 bpm variation across skin tones, findings supported by Sañudo et al. (2019) and Shcherbina et al. (2017) [7,10].”
From Photoplethysmography in Diverse Skin Tones: Evaluating Bias in Smartwatch Health Monitoring (2025) · cites this paper as [7]
The Results report mean Apple Watch–Polar biases of −2, −2, and −1 bpm for skin types II, III, and IV during exercise, supporting a small average difference across the tested groups. But the study tested only those three skin types during rest and cycling, and its 95% limits of agreement extend beyond 5 bpm; it does not establish less than 5 bpm variation for individual measurements across skin tones generally. (LLM, conf=0.84)
Experimental — accuracy not yet measuredErrors during exercise monitoring may result in inappropriate training intensities or misleading recovery assessments.
“Errors during exercise monitoring may result in inappropriate training intensities or misleading recovery assessments [7,8,9].”
From Photoplethysmography in Diverse Skin Tones: Evaluating Bias in Smartwatch Health Monitoring (2025) · cites this paper as [7]
The Perspectives section (page unavailable) says heart-rate monitors are used to control exercise intensity and that measurement accuracy matters when prescribing activity. The Results section (page unavailable) reports small measurement differences during exercise, supporting a potential concern about training intensity. The paper does not address recovery assessments. (LLM, conf=0.84)
Experimental — accuracy not yet measuredFour of the ten included studies found no difference in heart rate accuracy between participants of different skin tones.
“Four studies noted no effect of user skin tone on accuracy.”
From Accuracy of heart rate measurement with wrist-worn wearable devices in various skin tones: a systematic review (2023) · cites this paper as [1]
In three of the included studies, skin tone was the primary variable considered in the accuracy of wrist-worn heart rate monitors.
“In three of the included studies, skin tone was the primary variable considered in the accuracy of wrist-worn heart rate monitors [1, 2, 14].”
From Accuracy of heart rate measurement with wrist-worn wearable devices in various skin tones: a systematic review (2023) · cites this paper as [1]
Modern wearable devices rely on two components: photoplethysmography (PPG) and electrical sensors.
“The associated hardware in modern devices relies on two components: photoplethysmography (PPG), which passively monitors heart rate and rhythm, and electrical sensors, which require the user to remain still and touch the device with their opposite hand throughout the detection period [1].”
From Accuracy of heart rate measurement with wrist-worn wearable devices in various skin tones: a systematic review (2023) · cites this paper as [1]
PPG relies on LEDs projecting light onto the skin and photodetectors measuring the quantity of reflected light.
“This technology relies on LEDs projecting light onto the skin, and photodetectors measuring the quantity of reflected light [1, 2].”
From Accuracy of heart rate measurement with wrist-worn wearable devices in various skin tones: a systematic review (2023) · cites this paper as [1]
Etiwy et al. and Sanudo et al. found that skin color did not influence heart rate accuracy.
“Etiwy et al. and Sanudo et al. similarly found that skin color did not influence heart rate accuracy [1, 9].”
From Accuracy of heart rate measurement with wrist-worn wearable devices in various skin tones: a systematic review (2023) · cites this paper as [1]
Electrical sensors require the user to remain still and touch the device with their opposite hand throughout the detection period.
“The associated hardware in modern devices relies on two components: photoplethysmography (PPG), which passively monitors heart rate and rhythm, and electrical sensors, which require the user to remain still and touch the device with their opposite hand throughout the detection period [1].”
From Accuracy of heart rate measurement with wrist-worn wearable devices in various skin tones: a systematic review (2023) · cites this paper as [1]
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“Errors during exercise monitoring may result in inappropriate training intensities or misleading recovery assessments [7,8,9].”
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“Small wearable devices currently on the market (eg, Apple Watch, Garmin, Samsung, Fitbit, and Mi Band by Xiaomi) usually provide accurate heart rate data [13,19-24].”
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“For example, pho-toplethysmographic sensors tend to show reduced precision in individuals with darker skin tones or tattoos due to light absorption and scattering issues [ 144].”
Shapira‐Daniels, A., Kornej, J., Spartano, N. L., Wang, X., Zhang, Y., Pathiravasan, C. H., Liu, C., Trinquart, L., Borrelli, B., McManus, D. D., et al. (2023) · Journal of Medical Internet Research · doi:10.2196/43123 · Cited by 3 · see citing works
“Further, the accuracy of wearable devices among individuals with darker skin tones is unclear [49,50].”
Yamada, K., Enokida, Y., Kato, R., Imaizumi, J., Takada, T., & Ojima, H. (2023) · JMIR Human Factors · doi:10.2196/50891 · Cited by 3 · see citing works
Investigating Human Physiological Responses to Work-Related Stress
Uba, J., & Nuamah, J. K. (2023) · Proceedings of the Human Factors and Ergonomics Society Annual Meeting · doi:10.1177/21695067231192596 · Cited by 3 · see citing works
“Several studies have therefore utilized Apple watches to measure HR and their results have revealed the accuracy of its measurement (Falter et al., 2019; Sañudo et al., 2019).”
MethodWhite, J. W., Pfledderer, C. D., Kinard, P., Beets, M. W., von Klinggraeff, L., Armstrong, B., Adams, E. L., Welk, G. J., Burkart, S. A., & Weaver, R. G. (2023) · International journal of exercise science · doi:10.70252/vnkn6618 · Cited by 3 · see citing works
Heart rate estimation using on-nail wearable photoplethysmography
Mohtadzar, N. A. A., Balaban, E., Beach, C., Taylor, P. S., Horne, R. J., Batchelor, J. C., & Casson, A. J. (2024) · Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC) · doi:10.1109/embc53108.2024.10782437 · Cited by 3 · see citing works
“This is consistent with several studies which also found no statistically significant differences in wearable HR measurement accuracy across skin tones [17], [18], although other studies contradict this, [13], [14].”
Improving participant representation in the era of digital clinical studies
Ramos, E., Baca-Motes, K., Pandit, J. A., & Ajayi, T. A. (2022) · Trends in Molecular Medicine · doi:10.1016/j.molmed.2022.07.004 · Cited by 2 · see citing works
Khodr, R., Kamal, L., Minerbi, A., & Gupta, G. (2024) · medRxiv · doi:10.1101/2024.01.04.24300784 · Cited by 2 · see citing works
“PPG-based technologies have historically been prone to errors, in part through motion artifacts and variability in skin complexion (Allen, 2007; Bent et al., 2020; Butler et al., 2016; Sañudo et al., 2019).”
BackgroundSchipper, R. M., Djibrillah, F. O., Roosink, M., Winkens, L. H. H., John, A., Hazebroek, E. J., Witteveen, A., & Berendsen, A. A. M. (2025) · doi:10.2196/preprints.87324 · Cited by 1 · see citing works
Análise da influência do tom de pele no sinal de fotopletismografia (PPG)
Rosa, A. G. R. D., Schmith, J., de Figueiredo, R. M., Prade, L. R., PINHEIRO, J. A., & Rigo, S. J. (2023) · doi:10.5753/sbcas.2023.229566
Nelson, B. W., Singh, S., Bennett, M., Chen, C., Shin, S., & Ghanbari, H. (2024) · Research Square · doi:10.21203/rs.3.rs-3882498/v1
Peyghan, M. R., Fallahi, M., Ghaemmaghami, S., & Parvizi, S. (2024) · SSRN Electronic Journal · doi:10.2139/ssrn.4865574
Wearable Devices for Remote Monitoring of Chronic Diseases: A Systematic Review (Preprint)Preprint
Tegegne, M. D., Kalhori, S. R. N., Haas, P., Sobotta, V. M. G., Warnecke, J. M., & Deserno, T. M. (2025) · doi:10.2196/preprints.74071
Weaver, R. G., Finnegan, O., White, J. W., Kiely, K., Nelakuditi, S., Ghosal, R., Brown, D. E., PATE, R. R., Welk, G. J., de Zambotti, M., et al. (2025) · Journal for the Measurement of Physical Behaviour · doi:10.1123/jmpb.2025-0028
Smart swim goggles accurately measure heart rate during swim training: A criterion validation study
Kits, A., Elder, N. C., Eisenhardt, D., Hamedani, Y. D., Hoskinson, R., Madeleine, P., Samani, A., Kristiansen, M. V., & Clarke, D. C. (2026) · Journal of Sports Sciences · doi:10.1080/02640414.2025.2610787
“A known challenge with PPG-based HR monitoring is the potential influence of skin tone on signal quality, though findings on this topic are mixed (Koerber et al., 2023; Mühlen et al., 2021; Sañudo et al., 2019).”
Jaber, H., Olsson, C. M., & Salvi, D. (2025) · IEEE International Conference on Metrology for eXtended Reality, Artificial Intelligence and Neural Engineering (MetroXRAINE) · doi:10.1109/metroxraine66377.2025.11340270
“A study in 2019 assessed how skin color influenced the accuracy of heart rate measurements during exercise with an Apple watch [9].”
Schipper, R. M., Djibrillah, F. O., Roosink, M., Winkens, L. H. H., John, A., Hazebroek, E. J., Witteveen, A., & Berendsen, A. A. M. (2026) · JMIR mhealth and uhealth · doi:10.2196/87324 · Cited by 1 · see citing works
“There were 46 men-dominant studies (n=2637 participants), 17 women-dominant studies (n=688 participants), 11 men-only (n=277 participants) [59, 121,135,146,157,164,167,174,199], and 3 women-only (n=31 participants) studies [35,136,213].”
Rojas‐Valverde, D., & Gamboa-Salas, J. C. (2026) · Revista de Ciencias del Ejercicio FOD · doi:10.29105/rce-fod.v21i2.184
- Authors
- Sañudo, B., De Hoyo, M., Muñoz-López, A., Perry, J., & Abt, G.
- Affiliations
- Universidad de Sevilla (ES)
- Mary Immaculate College (IE)
- University of Hull (GB)
- Corresponding author
- Sañudo, Borja
- Venue
- Journal of Medical Systems
- Published
- 2019-05-22
- Volume
- 43
- Issue
- 7
- Pages
- 195-195
- ISSN
- 0148-5598 (ISSN-L)
- 1573-689X
- OpenAlex
- W2945549072
- Cited by
- 48
- References
- 22
- Citations by year
- 2026: 4 · 2025: 10 · 2024: 7 · 2023: 10 · 2022: 7 · 2021: 6 · 2020: 4
- FWCI
- 1.50
- Type
- journal article
- Language
- en
- Open access
- Locations
- Journal of Medical Systems (publishedVersion)
- PubMed (publishedVersion)
- Repository@Hull (Worktribe) (University of Hull) (submittedVersion, cc-by)
- Deposito de Investigacion Universidad de Sevilla (University of Seville) (submittedVersion, other-oa)
- Topics
- Physical Sciences › Engineering › Biomedical Engineering › Non-Invasive Vital Sign Monitoring
- Health Sciences › Medicine › Complementary and alternative medicine › Cardiovascular and exercise physiology
- Health Sciences › Medicine › Cardiology and Cardiovascular Medicine › Heart Rate Variability and Autonomic Control
- Keywords
- photoplethysmography, heart rate measurement, skin pigmentation, Fitzpatrick skin type, Apple Watch, wearable devices, exercise intensity, cycle ergometer test, measurement accuracy
- MeSH terms
- Wearable Electronic Devices, Adult, Exercise Test, Heart Rate, Humans, Male, Monitoring, Physiologic, Pilot Projects, Skin Pigmentation, Photoplethysmography, Young Adult
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