Differences in accelerometer-derived physical activity and sedentary time among toddlers between two procedures for removing naps

Background: Measuring physical activity and sedentary time in the early years (0-4 years) with accelerometers presents unique challenges due to daytime naps. Currently, an established procedure to determine daytime naps from accelerometer data in this age group does not exist. The purpose of this study was to examine differences in physical activity and sedentary time in a sample of toddlers between two procedures to remove naps.

Methods: This study includes 89 toddlers (19.7±5.5, mean±SD) from Edmonton, Canada. Participants wore ActiGraph accelerometers for 7 consecutive days during daytime hours. Procedure one removed naps through a regular non-wear time (NWT) data reduction procedure (≥20 min of consecutive zeros) and procedure two removed naps through NWT combined with parental log (NWT+log). Sedentary time (<25 counts/15 s), light-intensity physical activity (LPA; 25-420 counts/15 s), moderate- to vigorous-intensity physical activity (MVPA; >420 counts/15 s) were derived after each procedure and paired t-test compared measures.

Results: Mean h/day of MVPA, LPA, sedentary time, and total wear time when using the NWT procedure were 59.3±22.4, 236.4±40.1, 319.0±70.2, and 614.7±88.4, respectively. Mean h/day of MVPA, LPA, sedentary time, and total wear time when using the NWT+log procedure were 57.6±22.0, 229.2±40.3, 294.9±69.7, and 581.8±88.3, respectively. There were significant mean differences in MVPA, LPA, and sedentary time between the two procedures (P<0.001).

Conclusions: Different procedures for removing naps impact physical activity and sedentary time estimates. Future development of an accelerometer algorithm to determine daytime naps could reduce the burden of parental logs and overcome precision issues associated with them.