Temporal relationships between screen-time and physical activity with cardiorespiratory fitness in English Schoolchildren: A 2-year longitudinal study

Objective: To determine the temporal relationships screen-time and physical activity have with cardiorespiratory fitness. Method: Measures were made over two years (2008-2010) in 1500 participants aged 11.5 (SD 0.5) years at baseline. Results: Tracking coefficients were low-to-moderate for all measures. At follow-up, 25% of participants moved from having low (< 2. h) to high (≥ 2. h) daily screen-time and 6% became unfit according to FITNESSGRAM standards. Baseline screen-time was the strongest univariate predictor of becoming unfit. Multivariate analysis controlling for decimal age, BMI and deprivation confirmed baseline screen-time as the strongest independent predictor of becoming unfit over the 2-year study period (OR 2.4; 95%CI:1.4-4.0). Current (OR 2.3; 95%CI:1.3-4.0) and previous (OR 1.7; 95%CI:1.0-2.9) physical activity levels also independently predicted becoming unfit. Conclusion: There is currently no guidance for limiting screen-time in UK children. These longitudinal data add to the cross-sectional evidence of lower physical activity and fitness in children reporting ≥ 2. h daily screen-time. More importantly, these data demonstrate that high screen-time during childhood is an independent predictor of lower cardiorespiratory fitness in adolescence. © 2012 Elsevier Inc..