Excessive screen time was associated with lower cardiorespiratory fitness in school-aged children independent of overall physical activity levels, with this association being significant specifically among boys but not girls.
Key Findings
Results
Screen time had a significant main effect on VO2max after controlling for total physical activity.
Children in the high screen time category had significantly lower adjusted VO2max values than those in the low and moderate screen time groups
The effect size (partial η² = 0.04) indicates a small but statistically significant effect
Total physical activity as measured by PAQ-C was included as a covariate, meaning the screen time effect was independent of physical activity levels
Results
A significant interaction between sex and screen time on cardiorespiratory fitness was found.
The sex × screen time interaction was statistically significant: F(2,299) = 4.47, p = 0.01, partial η² = 0.03
Higher screen time was associated with lower cardiorespiratory fitness specifically in boys
No significant association between screen time and cardiorespiratory fitness was observed in girls
No significant main effect of sex alone on VO2max was observed
Methods
The study sample consisted of 306 Croatian school-aged children with a mean age of approximately 9.9 years.
Total sample: 306 children (163 girls, 143 boys)
Mean age: 9.89 ± 0.60 years
Cross-sectional study design conducted in Croatia
Cardiorespiratory fitness was assessed using the 20 m shuttle run test with VO2max estimated accordingly
Screen time was self-reported via questionnaire and categorized into three groups: low, moderate, and high
Methods
Physical activity was measured using the Physical Activity Questionnaire for Children (PAQ-C) and included as a covariate in analyses.
PAQ-C was used to assess total physical activity levels
Physical activity was controlled for statistically in the ANCOVA model
The significant screen time effect persisted even after adjusting for total physical activity, indicating an independent association
This approach allowed the authors to separate the effects of screen time from those of overall physical activity on cardiorespiratory fitness
Background
The relationship between screen time and cardiorespiratory fitness in school-aged children is described as inconsistent in the existing literature.
The authors note that prior literature shows inconsistent findings, particularly when overall physical activity is considered
Excessive screen time is characterized as an increasingly prevalent form of sedentary behavior among school-aged children
The study was motivated by the need to examine this association while controlling for total physical activity and examining sex differences
The authors frame excessive screen time as potentially adversely affecting various health indicators including cardiorespiratory fitness
What This Means
This research suggests that children who spend more time in front of screens have lower cardiovascular fitness levels, and that this relationship holds true even when accounting for how physically active those children are overall. The study followed 306 Croatian children around age 10, measuring their fitness using a running test and asking them about their screen time and physical activity habits. Children who reported the highest amounts of screen time had notably lower estimated aerobic capacity (VO2max) compared to children with low or moderate screen time, regardless of how much they exercised.
One of the more notable findings is that this effect appears to be specific to boys. When the researchers looked at boys and girls separately, higher screen time was linked to poorer cardiorespiratory fitness in boys, but no such pattern was detected in girls. The reasons for this sex difference are not fully explained by the study, but the finding suggests that the health impact of screen time on fitness may not be the same for all children.
This research suggests that simply encouraging children to be more physically active may not be enough to protect their cardiovascular fitness if they are also spending very large amounts of time on screens. The findings point toward the potential value of public health efforts that both promote physical activity and set limits on recreational screen time, particularly for boys. However, because the study was cross-sectional (a snapshot in time), it cannot definitively prove that screen time causes lower fitness — it is also possible that children who are less fit tend to spend more time on screens.
Check Your Own Numbers
Upload your bloodwork. We'll cross-reference your results against this study and 4,700 others.
Badrić M, Roca Badrić L, Nikolić I, Novak D, Mraković S. (2026). Screen time and cardiorespiratory fitness in school-aged children: a sex-specific association independent of physical activity-evidence from Croatia.. Frontiers in public health. https://doi.org/10.3389/fpubh.2026.1928966