Screen time and cardiorespiratory fitness in school-aged children: a sex-specific association independent of physical activity-evidence from Croatia.

BACKGROUND: Excessive screen time has become an increasingly prevalent form of sedentary behavior among school-aged children and may adversely affect various health indicators, including cardiorespiratory fitness. However, the relationship between screen time and cardiorespiratory fitness remains inconsistent in the literature, particularly when overall physical activity is considered. This study aimed to examine the association between screen time and cardiorespiratory fitness in school-aged children while controlling for total physical activity and to determine whether sex differences exist in this relationship. METHODS: A total of 306 school-aged children (163 girls, 143 boys; mean age 9.89 ± 0.60 years) participated in this cross-sectional study. Cardiorespiratory fitness was assessed using the 20 m shuttle run test, and maximal oxygen uptake (VO2max) was estimated accordingly. Screen time was assessed using a self-reported questionnaire and categorized into three groups (low, moderate, high). Total physical activity was assessed using the Physical Activity Questionnaire for Children (PAQ-C) and included as a covariate. A two-way analysis of covariance (ANCOVA) was conducted to examine the effects of sex and screen time on VO2max while controlling for physical activity. RESULTS: Results indicate a significant main effect of screen time on VO2max after adjusting for total physical [F(2,299) = 6.40, p < 0.001, partial η2 = 0.04]. Children in the high screen time category had significantly lower adjusted VO2 max values than those in the low and moderate groups. Although no significant main effect of sex was observed, a significant interaction between sex and screen time was found [F(2,299) = 4.47, p = 0.01, partial η2 = 0.03]. Specifically, higher screen time was associated with lower cardiorespiratory fitness in boys, whereas no significant association was observed in girls. CONCLUSION: These findings suggest that excessive screen time may be associated with lower cardiorespiratory fitness in children, independent of overall physical activity levels, particularly among boys. These findings support public health strategies aimed at limiting excessive recreational screen time while promoting regular physical activity among children.