Temporal relationships between screen-time and physical activity with cardiorespiratory fitness in English schoolchildren: a 2-year longitudinal study.

ABSTRACT

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 (<2h) 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%CI1.4-4.0). Current (OR 2.3; 95%CI1.3-4.0) and previous (OR 1.7; 95%CI1.0-2.9) 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.