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. 2019 Jul 29;2:71. doi: 10.1038/s41746-019-0149-2

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 4 — Wearable sensors monitor the physiological status (heart rate, muscle oxygen saturation, and sleep) of the athlete. a Bland Altman plots for all wearable wrist-sensors compared to the Polar RS400. x-axis: Mean of PolarRS400 and tested device; y-axis: PolarRS40 and tested device. b SmO₂ results for a representative subject during an incremental cycling test. The Humon Beta SmO₂ (red line) and MetaOx SmO₂ (green line) absolute values are 3–5% different; however, the overall trend holds for the duration of the exercise. The vertical lines indicate the time point that the power on the bike was changed and the numbers on top of the graph represent the power level (Watts) at which the subject was cycling. c Mean absolute percent error for various wearable devices during total sleep time. The numbers denoted next to each bar represent the mean absolute percentage error values which were used to calculate the absolute difference between each monitor and the sleep diary values. Figures were reproduced with permission from Stahl et al.¹⁰² a, Farzam et al.¹¹⁷ b, and Lee et al.¹³¹ c