title: Independence of physical activity and screen time as predictors of cardiorespiratory fitness in youth.
abstract: BACKGROUND
  Screen time (ST) is associated with physical activity (PA) levels. We aimed to investigate the relationship between ST and fitness.
  
  
  METHODS
  We assessed fitness and daily ST in 7,466 10-16-y-old schoolchildren from the east of England. The differences in fitness between ST groups, and the association between ST and fitness were assessed.
  
  
  RESULTS
  ST was negatively associated with fitness in boys of all ages (P < 0.001) and girls in grades 6-9 (P < 0.005). Boys were less likely to be fit if they reported >2 h/d ST (odds ratio (OR): 0.70, 95% confidence interval (CI): 0.58-0.85) or >4 h/d (OR: 0.45, 95% CI: 0.35-0.57) ST, as were girls reporting >4 h/d ST (OR: 0.58, 95% CI: 0.43-0.78). Controlling for PA levels attenuated these odds in boys reporting >2 h/d ST (OR: 0.81, 95% CI: 0.66-0.91) or >4 h/d ST (OR: 0.65, 95% CI: 0.50-0.84) and in girls reporting >4 h/d ST (OR: 0.68, 95% CI: 0.50-0.93).
  
  
  CONCLUSIONS
  These first data from English children show a negative association between ST and fitness in youth. Of note, very high levels of daily ST (>4 h) are associated with poor fitness. Some of the associations were mediated by PA levels. Our data support international recommendations to limit ST to <2 h/d; we believe such guidance should be issued in the United Kingdom.
authors: Centre for Sports and Exercise Science, School of Biological Sciences, University of Essex, Colchester, UK.
authors: Gavin R H
authors: GR
authors: Sandercock
authors: Ayodele A
authors: AA
authors: Ogunleye
mesh_terms: D000293:Adolescent; D002320:Cardiovascular Physiological Phenomena; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D010809:Physical Fitness; D012143:Respiratory Physiological Phenomena