Monte Carlo analysis of optical heart rate sensors in commercial wearables: The effect of skin tone and obesity on the photoplethysmography (PPG) signal
Open accessAbstract
Commercially available wearable devices have been used for fitness and health management and their demand has increased over the last ten years. These “general wellness” and heart-rate monitoring devices have been cleared by the Food and Drug Administration for over-the-counter use, yet anecdotal and more systematic reports seem to indicate that their error is higher when used by individuals with elevated skin tone and high body mass index (BMI). In this work, we used Monte Carlo modeling of a photoplethysmography (PPG) signal to study the theoretical limits of three different wearable devices (Apple Watch series 5, Fitbit Versa 2 and Polar M600) when used by individuals with a BMI range of 20 to 45 and a Fitzpatrick skin scale 1 to 6. Our work shows that increased BMI and skin tone can induce a relative loss of signal of up to 61.2% in Fitbit versa 2, 32% in Apple S5 and 32.9% in Polar M600 when considering the closest source-detector pair configuration in these devices.
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Ajmal et al. quantified up to a 15% drop in PPG signal quality (AC/DC ratio) between Fitzpatrick type I and VI skin.
“Ajmal et al. [12] quantified this impact using Monte Carlo simulations, reporting up to a 15% drop in signal quality (AC/DC ratio) between Fitzpatrick type I and VI skin.”
From PPG-Based Heart Rate Accuracy in Hispanic Adults with Fitzpatrick III–V Skin Tones: An Evaluation of Body Composition and Skin-Tone Effects (2026) · cites this paper as [12]
When skin tone and obesity co-occur, the combined effect is more severe; Ajmal et al. noted a compounded degradation in signal quality when simulating a type VI skin tone with BMI > 40, with AC/DC ratio dropping more than 60%.
“Ajmal et al. [12] noted a compounded degradation in signal quality when simulating a type VI skin tone with BMI > 40, particularly in devices with shallow optical penetration depth like the Fitbit Versa 2. The AC/DC ratio dropped more than 60%”
From PPG-Based Heart Rate Accuracy in Hispanic Adults with Fitzpatrick III–V Skin Tones: An Evaluation of Body Composition and Skin-Tone Effects (2026) · cites this paper as [12]
Ajmal et al. observed over a 60% drop in AC/DC signal strength between normal-weight and morbidly obese individuals.
“Ajmal et al. [12] observed over a 60% drop in AC/DC signal strength between normal-weight and morbidly obese individuals.”
From PPG-Based Heart Rate Accuracy in Hispanic Adults with Fitzpatrick III–V Skin Tones: An Evaluation of Body Composition and Skin-Tone Effects (2026) · cites this paper as [12]
Pooled comparisons by BMI category did not reach significance; however, several device-level contrasts indicated small directional biases with higher adiposity.
“In contrast, pooled comparisons by BMI category did not reach significance; however, several device-level contrasts indicated small directional biases with higher adiposity (e.g., [12,13]).”
From PPG-Based Heart Rate Accuracy in Hispanic Adults with Fitzpatrick III–V Skin Tones: An Evaluation of Body Composition and Skin-Tone Effects (2026) · cites this paper as [12]
Cites
Optical properties of biological tissues: A review
Jacques, S. L. (2013) · Physics in Medicine and Biology · doi:10.1088/0031-9155/58/11/r37 · Cited by 4,008 · see citing works
MCML—Monte Carlo modeling of light transport in multi-layered tissues
Wang, L. V., Jacques, S. L., & Zheng, L. (1995) · Computer Methods and Programs in Biomedicine · doi:10.1016/0169-2607(95)01640-f · Cited by 3,330 · see citing works
Smart wearable devices in cardiovascular care: Where we are and how to move forward
Bayoumy, K., Gaber, M., Elshafeey, A., Mhaimeed, O., Dineen, E. H., Marvel, F. A., Martin, S. S., Muse, E. D., Turakhia, M. P., Tarakji, K. G., et al. (2021) · Nature Reviews Cardiology · doi:10.1038/s41569-021-00522-7 · Cited by 829 · see citing works
OPTICAL PROPERTIES OF SKIN, SUBCUTANEOUS, AND MUSCLE TISSUES: A REVIEW
Bashkatov, A. N., Genina, E. A., & Tuchin, V. V. (2011) · Journal of Innovative Optical Health Sciences · doi:10.1142/s1793545811001319 · Cited by 765 · see citing works
Sandby-Møller, J., Poulsen, T., & Wulf, H. C. (2003) · Acta Dermato-Venereologica · doi:10.1080/00015550310015419 · Cited by 737 · see citing works
Investigating sources of inaccuracy in wearable optical heart rate sensors
Bent, B., Goldstein, B. A., Kibbe, W. A., & Dunn, J. P. (2020) · npj Digital Medicine · doi:10.1038/s41746-020-0226-6 · Cited by 673 · cited 2× · see citing works
“In contrast to these findings, recent experimental studies seem to indicate that although activities may lead to inaccuracy in heart rate measurements using commercial wearable devices, skin tone is not a source of error [9,18].”
BackgroundResultShcherbina, A., Mattsson, C., Waggott, D., Salisbury, H., Christle, J., Hastie, T., Wheeler, M., & Ashley, E. (2017) · Journal of Personalized Medicine · doi:10.3390/jpm7020003 · Cited by 625 · see citing works
The use of photoplethysmography for assessing hypertension
Elgendi, M., Fletcher, R., Liang, Y., Howard, N., Lovell, N. H., Abbott, D., Lim, K., & Ward, R. (2019) · npj Digital Medicine · doi:10.1038/s41746-019-0136-7 · Cited by 625 · see citing works
The Cutaneous Microcirculation
Braverman, I. M. (2000) · Journal of Investigative Dermatology Symposium Proceedings · doi:10.1046/j.1087-0024.2000.00010.x · Cited by 488 · see citing works
Effects of skin pigmentation on pulse oximeter accuracy at low saturation
Bickler, P. E., Feiner, J. R., & Severinghaus, J. W. (2005) · Anesthesiology · doi:10.1097/00000542-200504000-00004 · Cited by 427 · see citing works
Accuracy of Heart Rate Watches: Implications for Weight Management
Wallen, M. P., Gomersall, S. R., Keating, S. E., Wisløff, U., & Coombes, J. S. (2016) · PLOS ONE · doi:10.1371/journal.pone.0154420 · Cited by 336 · see citing works
Fitzpatrick skin typing: applications in dermatology
Sachdeva, S. (2009) · Indian Journal of Dermatology, Venereology and Leprology · doi:10.4103/0378-6323.45238 · Cited by 311 · see citing works
El-Hajj, C., & Kyriacou, P. A. (2020) · Biomedical Signal Processing and Control · doi:10.1016/j.bspc.2020.101870 · Cited by 300 · see citing works
Oltulu, P., İnce, B., Kökbudak, N., Fındık, S., & Kılınç, F. (2018) · Turkish Journal of Plastic Surgery · doi:10.4103/tjps.tjps_2_17 · Cited by 276 · see citing works
Heart Rate Estimation From Wrist-Worn Photoplethysmography: A Review
Biswas, D., Simões‐Capela, N., Hoof, C. A. V., & Helleputte, N. V. (2019) · IEEE Sensors Journal · doi:10.1109/jsen.2019.2914166 · Cited by 263 · see citing works
Healthcare wearable devices: an analysis of key factors for continuous use intention
Lee, S. M., & Lee, D. (2020) · Service Business · doi:10.1007/s11628-020-00428-3 · Cited by 218 · see citing works
Friebel, M. F., Helfmann, J., Netz, U. J., & Meinke, M. C. (2009) · Journal of Biomedical Optics · doi:10.1117/1.3127200 · Cited by 182 · see citing works
Establishing the diffuse correlation spectroscopy signal relationship with blood flow
Boas, D. A., Sakadžić, S., Selb, J. J., et al. (2016) · Neurophotonics · doi:10.1117/1.nph.3.3.031412 · Cited by 181 · see citing works
New insights into the origin of remote PPG signals in visible light and infrared
Moço, A., Stuijk, S., & de Haan, G. (2018) · Scientific Reports · doi:10.1038/s41598-018-26068-2 · Cited by 170 · see citing works
Influence of skin type and wavelength on light wave reflectance
Fallow, B. A., Tarumi, T., & Tanaka, H. (2013) · Journal of Clinical Monitoring and Computing · doi:10.1007/s10877-013-9436-7 · Cited by 162 · see citing works
Reddy, R. K., Pooni, R., Zaharieva, D. P., Senf, B., El Youssef, J., Dassau, E., Doyle III, F. J., Clements, M. A., Rickels, M. R., Patton, S. R., et al. (2018) · JMIR mHealth and uHealth · doi:10.2196/10338 · Cited by 157 · see citing works
Validation of Biofeedback Wearables for Photoplethysmographic Heart Rate Tracking.
(2016) · PubMed Central · Cited by 150 · see citing works
Ries, A. L., Prewitt, L. M., & Johnson, J. J. (1989) · Chest · doi:10.1378/chest.96.2.287 · Cited by 145 · see citing works
Marti, D., Aasbjerg, R. N. N., Andersen, P. E. E., & Hansen, A. K. K. (2018) · Journal of Biomedical Optics · doi:10.1117/1.jbo.23.12.121622 · Cited by 145 · see citing works
Derraik, J. G. B., Rademaker, M., Cutfield, W. S., Pinto, T. E., Tregurtha, S., Faherty, A., Peart, J. M., Drury, P. L., & Hofman, P. L. (2014) · PLoS ONE · doi:10.1371/journal.pone.0086637 · Cited by 129 · see citing works
The influence of body mass index on skin susceptibility to sodium lauryl sulphate
Löffler, H., Aramaki, J. U. N., & Effendy, I. (2002) · Skin Research and Technology · doi:10.1046/j.0909-752x · Cited by 120 · see citing works
Microvascular imaging of the skin
Deegan, A. J., & Wang, R. K. (2019) · Physics in Medicine and Biology · doi:10.1088/1361-6560/ab03f1 · Cited by 112 · see citing works
Chatterjee, S., & Kyriacou, P. A. (2019) · Sensors · doi:10.3390/s19040789 · Cited by 86 · see citing works
Boonya-ananta, T., Rodriguez, A. J., Ajmal, A., Du Le, V. N., Hansen, A. K., Hutcheson, J. D., & Ramella-Roman, J. C. (2021) · Scientific Reports · doi:10.1038/s41598-021-82124-4 · Cited by 70 · see citing works
Self-citationKoenig, N., Seeck, A., Eckstein, J., Mainka, A., Huebner, T. A., Voss, A., & Weber, S. (2016) · Telemedicine Journal and e-Health · doi:10.1089/tmj.2015.0212 · Cited by 60 · see citing works
Yan, L., Hu, S., Alzahrani, A., Alharbi, S., & Blanos, P. (2017) · Biosensors · doi:10.3390/bios7020022 · Cited by 40 · see citing works
Adamska, A., Araszkiewicz, A., Piłaciński, S., et al. (2018) · Microvascular Research · doi:10.1016/j.mvr.2018.10.002 · Cited by 32 · see citing works
Excessive weight favours skin physiology-up to a point: Another expression of the obesity paradox
Monteiro Rodrigues, L. M., Palma, L., Santos, O., Almeida, M. A., Bujan, J., & Tavares, L. (2017) · Skin Pharmacology and Physiology · doi:10.1159/000464338 · Cited by 25 · see citing works
Cheng, C., Daskalakis, C., & Falkner, B. E. (2009) · Journal of Clinical Hypertension · doi:10.1111/j.1751-7176.2009.00231.x · Cited by 22 · see citing works
Vascular contrast in narrow-band and white light imaging
Le, V. N. D., Wang, Q., Gould, T., et al. (2014) · Applied Optics · doi:10.1364/ao.53.004061 · Cited by 22 · see citing works
Monte Carlo modeling of light-tissue interactions in narrow band imaging
Le, V. N. D., Wang, Q., Ramella‐Roman, J. C., et al. (2012) · Journal of Biomedical Optics · doi:10.1117/1.jbo.18.1.010504 · Cited by 12 · see citing works
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Recommendations to advance digital health equity: A systematic review of qualitative studies
Wilson, S., Tolley, C., Mc Ardle, R., Lawson, L., Beswick, E., Hassan, N., Slight, R., & Slight, S. (2024) · npj Digital Medicine · doi:10.1038/s41746-024-01177-7 · Cited by 139 · see citing works
Kim, E. H., Jenness, J. L., Miller, A. B., Halabi, R., de Zambotti, M., Bagot, K. S., Baker, F. C., & Pratap, A. (2023) · JAMA Network Open · doi:10.1001/jamanetworkopen.2023.5681 · Cited by 53 · see citing works
Kostrna, J., Oparina, E., Palacios, C., Rodriguez, A. J., Pei, J., Ajmal, A., & Ramella-Roman, J. C. (2026) · Sensors · doi:10.3390/s26102922 · Cited by 2 · see citing works
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- Authors
- Ajmal, Boonya-Ananta, T., Rodriguez, A. J., Du Le, V. N., & Ramella-Roman, J. C.
- Affiliations
- Florida International University (US)
- Florida International University
- ORCID
- Du Le, V. N.
- Venue
- Biomedical Optics Express
- Publisher
- Optica Publishing Group
- Published
- 2021-11-10
- Volume
- 12
- Issue
- 12
- Pages
- 7445
- ISSN
- 2156-7085 (ISSN-L)
- PMC
- PMC8713672
- OpenAlex
- W3206086935
- Semantic Scholar
- aa034f710e946f66c84c619586ac0b6d5846e76e
- Cited by
- 79
- References
- 36
- Citations by year
- 2026: 15 · 2025: 25 · 2024: 17 · 2023: 14 · 2022: 8
- FWCI
- 2.96
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Locations
- Biomedical Optics Express (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- Funders
- National Science Foundation (1648451)
- Topics
- Physical Sciences › Engineering › Biomedical Engineering › Non-Invasive Vital Sign Monitoring
- Health Sciences › Medicine › Radiology, Nuclear Medicine and Imaging › Optical Imaging and Spectroscopy Techniques
- Health Sciences › Medicine › Cardiology and Cardiovascular Medicine › Heart Rate Variability and Autonomic Control
- Keywords
- photoplethysmography, wearable devices, heart rate monitoring, skin tone, obesity, body mass index, signal loss, Apple Watch, Monte Carlo simulation
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