title: 24 h Accelerometry: impact of sleep-screening methods on estimates of sedentary behaviour and physical activity while awake.
abstract: Although accelerometers can assess sleep and activity over 24 h, sleep data must be removed before physical activity and sedentary time can be examined appropriately. We compared the effect of 6 different sleep-scoring rules on physical activity and sedentary time. Activity and sleep were obtained by accelerometry (ActiGraph GT3X) over 7 days in 291 children (51.3% overweight or obese) aged 4-8.9 years. Three methods removed sleep using individualised time filters and two methods applied standard time filters to remove sleep each day (9 pm-6 am, 12 am-6 am). The final method did not remove sleep but simply defined non-wear as at least 60 min of consecutive zeros over the 24-h period. Different methods of removing sleep from 24-h data markedly affect estimates of sedentary time, yielding values ranging from 556 to 1145 min/day. Estimates of non-wear time (33-193 min), wear time (736-1337 min) and counts per minute (384-658) also showed considerable variation. By contrast, estimates of moderate-to-vigorous activity (MVPA) were similar, varying by less than 1 min/day. Different scoring methods to remove sleep from 24-h accelerometry data do not affect measures of MVPA, whereas estimates of counts per minute and sedentary time depend considerably on which technique is used.
authors.affiliation: a Department of Medicine , University of Otago , Dunedin , New Zealand.
authors.forename: Kim
authors.initials: K
authors.lastname: Meredith-Jones
authors.affiliation: b Department of Preventive and Social Medicine , University of Otago , Dunedin , New Zealand.
authors.forename: Sheila
authors.initials: S
authors.lastname: Williams
authors.affiliation: c Department of Women's and Children's Health , University of Otago , Dunedin , New Zealand.
authors.forename: Barbara
authors.initials: B
authors.lastname: Galland
authors.affiliation: d School of Physical Education, Sport and Exercise Sciences , University of Otago , Dunedin , New Zealand.
authors.forename: Gavin
authors.initials: G
authors.lastname: Kennedy
authors.affiliation: a Department of Medicine , University of Otago , Dunedin , New Zealand.
authors.forename: Rachael
authors.initials: R
authors.lastname: Taylor
mesh_terms: D061725:Accelerometry / Q000379:methods*; D050218:Body Fat Distribution; D015992:Body Mass Index; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D057185:Sedentary Behavior; D012890:Sleep; D013997:Time Factors; D065927:Waist-Height Ratio
keywords: 24-h accelerometry; Physical activity; sedentary sleep