Abstract MP018: Moderate-to-Vigorous Physical Activity: Evidence for a Displacement Effect on Sedentary Behaviour

Background: Sedentary behaviour has detrimental health consequences, distinct from those of physical inactivity. An individual can be both highly active and highly sedentary: While the displacement hypothesis proposes that time spent active displaces time that would otherwise be spent sedentary, the compensation hypothesis suggests that increased physical activity (PA) may be associated with increased sedentary behaviour (SED) in non-active time. Objectives: The aim was to assess whether higher levels of childhood participation in moderate to vigorous PA (MVPA) are associated with higher levels of SED, or whether time spent in SED is displaced by higher levels of MVPA. Methods: Participants were 290 boys and 245 girls aged 8–10 years in the QUebec Adipose and Lifestyle InvesTigation in Youth (QUALITY) study. PA and SED were assessed by accelerometer over a 1-week period (SED ≤ 100 cpm, MVPA ≥ 2296 cpm), and quantified as mean time spent per day. Total PA was the sum of light PA + MVPA. Self-reported data included sports participation (number of teams), television viewing and computer/video game use (hours/day). Spearman correlations and multiple linear regression (adjusting for age, sex, body mass index, Tanner stage, parental education, accelerometer wear-time) were used to assess associations between PA and SED variables. Results: Higher MVPA and VPA were negatively correlated with SED (r=−0.44 and −0.35; p<0.001), and positively correlated with total PA (r=0.58 and 0.45; p<0.001). SED was negatively correlated with TPA (r=−0.65, p<0.001). Only weak correlations were found between MVPA and sports participation, the latter not associated with SED. MVPA and VPA were not significantly correlated with TV, computer/video or total screen time; objectively measured SED was only weakly associated with specific sedentary behaviours. On average, for each additional 10 minutes of MVPA, children spent 14 minutes less in SED, or for each additional 5 minutes of VPA, 10 minutes less in SED. Associations were stronger in overweight/obese children compared to healthy weight children. Conclusions: Higher levels of MVPA in children displace SED, and are also associated with higher total PA over and above the additional amount of MVPA. The SED displacement benefits of higher MVPA may be greatest in overweight/obese children. Public health strategies should focus on both increasing PA and decreasing SED as essential targets to improve overall PA in children.

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