Screen-based sedentary behavior and cardiorespiratory fitness from age 11 to 13

The study's purpose was to determine whether time spent in screen-based sedentary behavior is associated with change in cardiorespiratory fitness (CRF) levels in children from age 11 to 13, adjusting for vigorous physical activity (VPA).

Participants were children (n = 2097) enrolled in the control arm of the HEALTHY Study, who performed 20-m shuttle run tests at ages 11 and 13. Self-reported screen time was used as a measure of sedentary behavior. Longitudinal quantile regression was used to model the influence of predictors on changes at the 10th, 25th, 50th, 75th, and 90th shuttle run lap percentiles. Screen time (h·d(-1)) was the main predictor, and adjustment was also made for VPA, body mass index, and household education.

In boys, more screen time was associated with fewer shuttle run laps completed from age 11 to 13 at the 25th, 50th, and 75th shuttle run lap percentiles; the strongest association was at the 75th shuttle run percentile (-0.57, 95% confidence interval = -0.93 to -0.21). In girls, more screen time was associated with fewer shuttle run laps completed from age 11 to 13 at the 50th, 75th, and 90th shuttle run lap percentiles; the strongest association was at the 90th shuttle run percentile (-0.65, -1.01 to -0.30). Borderline negative associations were found between screen time and shuttle run laps at the 10th shuttle run percentile in boys and girls (-0.28, -0.57 to 0.01, and -0.17, -0.41 to 0.06, respectively).

More screen time was associated with lower CRF from age 11 to 13, independent of VPA. However, the association was weakest at the lower tail of the CRF distribution.