Lauren Boag, AnnaGrace Gardner, Rebecca R. Rogers, Mallory R. Marshall, FACSM. Samford University, Birmingham, AL.

Photoplethysmography (PPG) is a non-invasive technology designed to measure volumetric and circulation changes in blood using low-intensity infrared light or green LED light. This technology is used in fitness tracking devices to estimate heart rate (HR). There is little research on how PPG technology is affected by skin tone, despite the possibility that skin with more melanin may not reflect light as well as lighter skin. The purpose of this study was to investigate the effects of melanin concentration in skin on the HR measurement accuracy of the Apple Watch Series 6, FitBit Versa 3, MI Band, Fitbit Inspire 2, Letsfit Smartwatch, and Garmin Vivo 4 in treadmill walking, and activities of daily living (climbing stairs, vacuuming, picking up toys, and carrying groceries). Participants were college-age adults whose skin tone was visually assessed as Type I/II (light skin tone), Type III/IV (medium skin tone), or Type V/VI (dark skin tone) utilizing the validated Fitzpatrick scale. Participants completed a single session of activity while wearing the devices in a randomized order on both wrists, as well as a Polar HR monitor (the gold standard measurement) fitted to their chest. They performed activities for 5 minutes each with a 3 minute rest period between each. The percent error for each device was calculated by the formula: [(known HR - device HR) / known HR) *100]. An independent t-test was used to compare the percent errors between groups. During the vacuuming, picking up toys, and carrying groceries trials, the Mi band had significantly greater error in the dark skin tone group compared to light or medium (p<0.05). There were no other differences between devices (p>0.05). These data suggest that the six tested devices work equally well in participants with all skin tones except for the Mi band in individuals with dark skin tone. Additional research on dark skin tones is required to further understand how melanin concentration affects PPG technology.

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