Why Are Children Different in Their Daily Sedentariness? An Approach Based on the Mixed-Effects Location Scale Model

Thayse Natacha Gomes; Donald Hedeker; Fernanda Karina dos Santos; Sara Pereira; Peter T Katzmarzyk; José A R Maia

doi:10.1371/journal.pone.0132192

Why Are Children Different in Their Daily Sedentariness? An Approach Based on the Mixed-Effects Location Scale Model

PLoS One. 2015 Jul 31;10(7):e0132192. doi: 10.1371/journal.pone.0132192. eCollection 2015.

Authors

Thayse Natacha Gomes¹, Donald Hedeker², Fernanda Karina dos Santos³, Sara Pereira¹, Peter T Katzmarzyk⁴, José A R Maia¹

Affiliations

¹ Center of Research, Education, Innovation and Intervention in Sport (CIFI2D), Kinanthropometry Lab, Faculty of Sport, University of Porto, Porto, Portugal.
² Department of Public Health Sciences, University of Chicago, Chicago, Illinois, United States of America.
³ Department of Physical Education and Sports Science, CAV, Federal University of Pernambuco, Vitória de Santo Antão, Pernambuco, Brazil.
⁴ Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, Louisiana, United States of America.

Abstract

This study aimed to investigate the between- and within-individual variability in sedentary time over seven days, using a mixed-effects location scale model. The sample comprised 686 Portuguese children (381 girls) aged 9-11 years, from 23 schools. Sedentary time was estimated by the Actigraph GT3X+ accelerometer, which was used 24 hours/day for 7 consecutive days; height, sitting height, and weight were measured, BMI was computed (WHO cut-points were used to classify subjects as normal weight or overweight/obese), and maturity offset was estimated. Information regarding the home environment was obtained by questionnaire. Results revealed that (i) children were more sedentary on Friday, but less so on Saturday and Sunday (compared to Monday), with significant variation between- and within-subjects (between-subject variance=0.800, within-subject variance=1.793, intra-subject correlation=0.308); (ii) there is a sex effect on sedentariness, with boys being less sedentary than girls (p<0.001), and the between-subject variance was 1.48 times larger for boys than girls; (iii) in terms of the within-subject variance, or erraticism, Tuesday, Wednesday and Friday have similar erraticism levels as Monday (Thursday has less, while Saturday and Sunday have more); in addition, girls (variance ratio=0.632, p<0.001), overweight/obese children (variance ratio=0.861, p=0.019), and those later mature (variance ratio=0.849, p=0.013) have less erraticism than their counterparts; (iv) the within-subject variance varied significantly across subjects (scale std dev=0.342±0.037, p<0.001); and (v) in the fixed part of the model, only biological maturation was positively related to sedentariness. This study demonstrated that there is significant between- and within-subject variability in sedentariness across a whole week. This implies that a focus on intra-individual variability, instead of only on mean values, would provide relevant information towards a more complete map of children's sedentary behaviour, which can be helpful when developing more efficient strategies to reduce sedentariness.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Accelerometry
Body Mass Index
Body Weight
Child
Exercise / physiology*
Female
Humans
Male
Motor Activity / physiology*
Obesity
Sedentary Behavior*
Sex Factors
Time Factors

Grants and funding

ISCOLE was funded by The Coca-Cola Company. The funder had no role in the study design, data collection and analysis, decision to publish or preparation of this manuscript.