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Effects of Frequency Filtering on Intensity and Noise in Accelerometer-Based Physical Activity Measurements

1
Center for Health and Performance, Department of Food and Nutrition, and Sport Science, University of Gothenburg, SE-40530 Gothenburg, Sweden
2
Institute of Neuroscience and Psychology, University of Gothenburg, 40530 Gothenburg, Sweden
3
Department of Medicine and Geriatrics, Sahlgrenska University Hospital/Östra, SE-416 50 Gothenburg, Sweden
4
Department of Biometry and Data Management, Leibniz Institute for Prevention Research and epidemiology (BIPS), DE-283 59 Bremen, Germany
5
Åstrand Laboratory of Work Physiology, The Swedish School of Sport and Health Sciences, SE-114 86 Stockholm, Sweden
6
Department of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, SE-413 90 Gothenburg, Sweden
*
Author to whom correspondence should be addressed.
Sensors 2019, 19(9), 2186; https://doi.org/10.3390/s19092186
Received: 10 April 2019 / Revised: 6 May 2019 / Accepted: 8 May 2019 / Published: 11 May 2019
(This article belongs to the Collection Sensors for Globalized Healthy Living and Wellbeing)
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Abstract

In objective physical activity (PA) measurements, applying wider frequency filters than the most commonly used ActiGraph (AG) filter may be beneficial when processing accelerometry data. However, the vulnerability of wider filters to noise has not been investigated previously. This study explored the effect of wider frequency filters on measurements of PA, sedentary behavior (SED), and capturing of noise. Apart from the standard AG band-pass filter (0.29–1.63 Hz), modified filters with low-pass component cutoffs at 4 Hz, 10 Hz, or removed were analyzed. Calibrations against energy expenditure were performed with lab data from children and adults to generate filter-specific intensity cut-points. Free-living accelerometer data from children and adults were processed using the different filters and intensity cut-points. There was a contribution of acceleration related to PA at frequencies up to 10 Hz. The contribution was more pronounced at moderate and vigorous PA levels, although additional acceleration also occurred at SED. The classification discrepancy between AG and the wider filters was small at SED (1–2%) but very large at the highest intensities (>90%). The present study suggests an optimal low-pass frequency filter with a cutoff at 10 Hz to include all acceleration relevant to PA with minimal effect of noise. View Full-Text
Keywords: calibration; ActiGraph; Axivity; children; adults; I.Family; LIV-2013 calibration; ActiGraph; Axivity; children; adults; I.Family; LIV-2013
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Fridolfsson, J.; Börjesson, M.; Buck, C.; Ekblom, Ö.; Ekblom-Bak, E.; Hunsberger, M.; Lissner, L.; Arvidsson, D. Effects of Frequency Filtering on Intensity and Noise in Accelerometer-Based Physical Activity Measurements. Sensors 2019, 19, 2186.

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