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Large Scale Population Assessment of Physical Activity Using Wrist Worn Accelerometers: The UK Biobank Study

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Doherty, A 
Jackson, D 
Hammerla, N 
Plötz, T 
Olivier, P 


BACKGROUND: Physical activity has not been objectively measured in prospective cohorts with sufficiently large numbers to reliably detect associations with multiple health outcomes. Technological advances now make this possible. We describe the methods used to collect and analyse accelerometer measured physical activity in over 100,000 participants of the UK Biobank study, and report variation by age, sex, day, time of day, and season. METHODS: Participants were approached by email to wear a wrist-worn accelerometer for seven days that was posted to them. Physical activity information was extracted from 100Hz raw triaxial acceleration data after calibration, removal of gravity and sensor noise, and identification of wear / non-wear episodes. We report age- and sex-specific wear-time compliance and accelerometer measured physical activity, overall and by hour-of-day, week-weekend day and season. RESULTS: 103,712 datasets were received (44.8% response), with a median wear-time of 6.9 days (IQR:6.5-7.0). 96,600 participants (93.3%) provided valid data for physical activity analyses. Vector magnitude, a proxy for overall physical activity, was 7.5% (2.35mg) lower per decade of age (Cohen's d = 0.9). Women had a higher vector magnitude than men, apart from those aged 45-54yrs. There were major differences in vector magnitude by time of day (d = 0.66). Vector magnitude differences between week and weekend days (d = 0.12 for men, d = 0.09 for women) and between seasons (d = 0.27 for men, d = 0.15 for women) were small. CONCLUSIONS: It is feasible to collect and analyse objective physical activity data in large studies. The summary measure of overall physical activity is lower in older participants and age-related differences in activity are most prominent in the afternoon and evening. This work lays the foundation for studies of physical activity and its health consequences. Our summary variables are part of the UK Biobank dataset and can be used by researchers as exposures, confounding factors or outcome variables in future analyses.



Accelerometry, Aged, Biological Specimen Banks, Exercise, Female, Humans, Male, Middle Aged, Public Health Surveillance, Seasons, Time Factors, United Kingdom, Wrist Joint

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PLoS One

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Public Library of Science (PLoS)
Medical Research Council (MC_UU_12015/3)
Medical Research Council (MC_UU_12015/1)
Department of Health (via National Institute for Health Research (NIHR)) (NF-SI-0512-10135)
Cambridge University Hospitals NHS Foundation Trust (CUH) (146281)
Medical Research Council (MC_U106179471)
Medical Research Council (MC_U106179473)
The UK Biobank Activity Project and the collection of activity data from participants was funded by the Wellcome Trust ( and the Medical Research Council ( The analysis was supported by the British Heart Foundation Centre of Research Excellence at Oxford ( [grant number RE/13/1/30181 to AD], the Li Ka Shing Foundation ( [to AD], the UK Medical Research Council ( [grant numbers MC_UU_12015/1 and MC_UU_12015/3 to NW and SB], the RCUK Digital Economy Research Hub on Social Inclusion through the Digital Economy (SiDE) ( [EP/G066019/1 to NH], the EPSRC Centre for Doctoral Training in Digital Civics ([EP/L016176/1 to DJ], and the National Institute for Health Research ( [SRF-2011-04-017 to MIT]. The MRC and Wellcome Trust played a key role in the decision to establish UK Biobank, and the accelerometer data collection. No funding bodies had any role in the analysis, decision to publish, or preparation of the manuscript.