title: Excessive sedentary time and low cardiorespiratory fitness in European adolescents: the HELENA study.
abstract: BACKGROUND
  The aims of this study were to examine what amount of sedentary time is associated with low cardiorespiratory fitness (CRF) in adolescents and whether this association is independent of physical activity.
  
  
  METHODS
  The study comprised 1808 adolescents aged 12.5-17.5 years from 10 European cities. Sedentary time and moderate-to-vigorous physical activity (MVPA) were measured by accelerometer. CRF was assessed by the 20 m shuttle-run test. Adolescents were divided into two groups (high/low) according to FITNESSGRAM guidelines. Receiver-operating characteristic (ROC) analysis was used to determine thresholds that best discriminate between high and low CRF in adolescents.
  
  
  RESULTS
  Adolescent girls had more sedentary time than boys (p<0.001). ROC analysis showed that girls spending ≥69% of waking time in sedentary activities had low CRF, but no significant threshold discriminated between high and low CRF in boys. Adolescent girls who exceeded this threshold had lower levels of CRF (p≤0.001) and were more likely to have a low CRF (OR 1.68, 95% CI 1.22 to 2.31) independent of centre, age and body mass index. The negative influence of excessive sedentary time on CRF remained significant (p=0.045) in adolescent girls who did not meet the physical activity guidelines (<60 min/day in MVPA) but was abolished (p>0.05) in those who met the recommendation (≥60 min/day in MVPA).
  
  
  CONCLUSIONS
  Excessive sedentary time is associated with low CRF in adolescent girls but not in boys. However, this adverse effect might be attenuated if adolescent girls meet the current physical activity guidelines.
authors.affiliation: Department of Biosciences and Nutrition at NOVUM, Unit for Preventive Nutrition, Karolinska Institutet, Huddinge, Sweden.
authors.forename: David
authors.initials: D
authors.lastname: Martinez-Gomez
authors.forename: Francisco B
authors.initials: FB
authors.lastname: Ortega
authors.forename: Jonatan R
authors.initials: JR
authors.lastname: Ruiz
authors.forename: Germán
authors.initials: G
authors.lastname: Vicente-Rodriguez
authors.forename: Oscar L
authors.initials: OL
authors.lastname: Veiga
authors.forename: Kurt
authors.initials: K
authors.lastname: Widhalm
authors.forename: Yannis
authors.initials: Y
authors.lastname: Manios
authors.forename: Laurent
authors.initials: L
authors.lastname: Béghin
authors.forename: Jara
authors.initials: J
authors.lastname: Valtueña
authors.forename: Anthony
authors.initials: A
authors.lastname: Kafatos
authors.forename: Denes
authors.initials: D
authors.lastname: Molnar
authors.forename: Luis A
authors.initials: LA
authors.lastname: Moreno
authors.forename: Ascension
authors.initials: A
authors.lastname: Marcos
authors.forename: Manuel J
authors.initials: MJ
authors.lastname: Castillo
authors.forename: Michael
authors.initials: M
authors.lastname: Sjöström
mesh_terms: D000293:Adolescent; D000886:Anthropometry / Q000379:methods; D015992:Body Mass Index; D002648:Child; D003430:Cross-Sectional Studies; D005080:Exercise Test / Q000379:methods; D005260:Female; D006801:Humans; D007899:Leisure Activities; D008297:Male; D009043:Motor Activity / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology*; D057185:Sedentary Behavior; D012727:Sex Characteristics