Association Between Sitting, Screen Time, Fitness Domains, and Fundamental Motor Skills in Children Aged 5–16 Years: Cross-Sectional Population Study

Background: To examine the associations between school-age children’s sedentary behavior, screen time, and 3 physical activity attributes: muscular strength, cardiorespiratory endurance (CRE), and fundamental movement skills. Methods: Cross-sectional survey of 2734 children in years 2 and 4 and 3671 adolescents in years 6, 8, and 10. Total sitting time, 6 screen time behaviors, and physical activity were measured by self-report. Muscular strength was assessed by standing broad jump; CRE by 20-m shuttle run test; and fundamental movement skills by process-oriented checklists. Associations between incremental sitting and screen time (in hours) and meeting the healthy zone of physical activity attributes were examined using logistic regression. Results: After adjusting for covariates and physical activity, children had lower odds of achieving the healthy zone for muscular strength and CRE for each hour of week (but not weekend) screen time. For adolescents, each hour of screen time per day was associated with lower odds of achieving the healthy fitness zone for CRE, locomotor skills, and overall healthy zone, and each hour of weekend screen time was associated with lower odds of achieving the healthy zone for most attributes and overall healthy zone. The associations were slightly stronger among adolescent girls than boys. The findings were similar for total sitting time. Conclusions: Screen time was associated with a lower likelihood to achieve healthy zones of physical activity attributes, and the effect was more consistent and slightly stronger among adolescents than children. This may suggest that the negative effects of screen time are incremental, emerging during adolescence.

Dynamics of Activity Time-of-Day Choice

This study explored travelers’ decision behavior in selecting activity start times. The study examined the problem in the context of the Agent-based Dynamic Activity Planning and Travel Simulation (ADAPTS) activity-based travel demand model for the Chicago, Illinois, metropolitan area. A unique feature of the ADAPTS framework is its consideration of planning horizons for various activity attributes. Naturally, the various attributes of an activity—such as start time, duration, location, party involvement, and mode of travel—can be planned in different time horizons. An attribute that is planned affects the choice of other activity attributes. Therefore, developing a true behavioral time-of-day choice model would not be possible unless the planning order of activity attributes and the dynamics of travelers’ decision-making processes are taken into account. Similarly, it can be argued that there should be fundamental differences in the time-of-day decision process when other attributes of the activity are not yet planned but are to be decided at a later time. The presented time-of-day model aims to capture the dynamics of this decision process by considering the planning time horizons of other attributes of the activity, as well as the outcomes of the decisions. The study adopted the discrete choice approach to model activity timing decisions and a hybrid utility maximization and developed a regret minimization model to account for the heterogeneity of decision rules across choice variables. Analysis of the estimation results and parameter elasticities indicates that higher expected travel time, variations in travel time, and schedule occupancy rates for different time choices can significantly increase the regret value of the corresponding choice and therefore affect the time-of-day choice.