Influence of Skin Pigmentation on the Accuracy of Photoplethysmographic Heart Rate During Exercise

The use of photoplethysmography to monitor heart rate (HR)—by measurement of light reflected from the cutaneous vascular bed—is an attractive technology for wearable devices because it is both inexpensive and noninvasive. However, higher melanin content of the epidermis may reduce the amount of light transmitted through the skin, limiting the widespread application of this technology. Previous studies examining the impact of skin tone on photoplethysmographic HR measurement accuracy have produced conflicting results and none objectively measured skin pigmentation. Objective and hypothesis: The aim of this study was to quantify the extent to which epidermal melanin content influences the accuracy of photoplethysmographic HR measurement during rest, exercise, and recovery. We hypothesized that darker skin pigmentation would result in greater error in photoplethysmographic HR measurement. Methods: Skin pigmentation was measured noninvasively using a colorimeter in 29 healthy adults (mean ± SD; age = 25 ± 5 y; White, n = 17; Black, n = 10; Middle Eastern, n = 1; Persian, n = 1); colorimeter measurements were used to calculate Individual Typology Angle (ITA°), a strong correlate of epidermal melanin. After resting for 5 min, participants cycled continuously in temperate conditions (22 °C) for 10 min each at 50%, 60%, 70%, and 80% of age-predicted maximal HR, respectively, followed by a 10-min seated recovery. Chest-worn HR (criterion; Polar H10) and photoplethysmographic HR from 3 devices (Apple Watch Series 8, Garmin vivosport 5, SlateSafety BAND V2) were recorded continuously and summarized into 30-s epochs for analysis. A linear mixed-effects model determined whether ITA° influences mean absolute error of HR (MAE HR ) for each device. Results: Bland-Altman analysis revealed excellent overall agreement [95% limits of agreement (LoA) ±5 bpm] with criterion HR for the Apple (bias = 0.0 bpm, 95% LoA = ±2.2 bpm) and Garmin (bias = 0.4 bpm, 95% LoA = ±4.0 bpm) devices, and good agreement (95% LoA ±10 bpm) for the SlateSafety (bias = 0.8 bpm, 95% LoA = ±8.2 bpm) device. Participants with dark skin (ITA° <10°; 34%) accounted for disproportionately higher rates of missing (Apple, 50%; Garmin, 33%; SlateSafety, 85%) and outlier (Apple, 61%; Garmin, 56%; SlateSafety, 62%) data. After removal of outliers (>3.29 x SD of MAE HR ), ITA° was not a significant predictor of MAE HR for Apple (P=0.64) or Garmin (P=0.25) watches. Darker skin was associated with higher MAE HR for the SlateSafety device (β=−0.01, P=0.001), meaning that MAE HR is ~1 bpm greater in individuals with darker skin (ITA° = −60°) compared to individuals with lighter skin (ITA° = +60°). Conclusion: Skin pigmentation, as ITA°, negatively impacts photoplethysmographic HR measurement for the tested devices. This study was supported by an equipment grant from SlateSafety (Atlanta, GA). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.