title: The independent associations of sedentary behaviour and physical activity on cardiorespiratory fitness.
abstract: BACKGROUND
  During childhood and adolescence, both physical activity (PA) and sedentary behaviour seem to influence cardiorespiratory fitness (CRF); however, the combined association of PA and sedentary behaviour remains to be understood. We analysed the combined association of objectively measured sedentary behaviour and moderate-to-vigorous intensity PA (MVPA) on CRF in Portuguese children and adolescents.
  
  
  METHODS
  The sample comprised 2506 Portuguese healthy children and adolescents aged 10-18 years, from a cross-sectional school-based study (2008). PA and sedentary behaviour were assessed with accelerometry. Participants were classified as meeting current PA guidelines for youth versus not meeting, and as low versus high sedentary (according to the median value of sedentary time/day by age and gender), and then grouped as follows: Low active-high sedentary; low active-low sedentary; high active-high sedentary; high active-low sedentary. CRF was assessed with the FITNESSGRAM 20 m shuttle-run test. Binary logistic regression models were constructed to verify the relationship between high CRF and the combined influence of MVPA/sedentary behaviour, adjusting for age, gender, body mass index and accelerometer wear time.
  
  
  RESULTS
  Participants classified as high active/low sedentary (OR=1.81; 95% CI 1.21 to 2.69), as well as those classified as low active/low sedentary (OR=1.27; 95% CI 1.01 to 1.61) were more likely to be fit, compared with those from the low-active/high-sedentary group.
  
  
  CONCLUSIONS
  MVPA and sedentary behaviour may act independently in their relation with CRF, and that MVPA levels may not overcome the deleterious influence of high-sedentary time in maximising CRF.
authors: Research Centre in Physical Activity, Health and Leisure, Faculty of Sport, University of Porto, Porto, Portugal Maia Institute of Higher Education, Maia, Portugal.
authors: Rute
authors: R
authors: Santos
authors: Research Centre in Physical Activity, Health and Leisure, Faculty of Sport, University of Porto, Porto, Portugal.
authors: Jorge
authors: J
authors: Mota
authors: Interdisciplinary Educational Research Institute, University of Wollongong, Wollongong, New South Wales, Australia.
authors: Anthony David
authors: AD
authors: Okely
authors: National Center for Chronic Disease Prevention and Health Promotion, Atlanta, Georgia, USA.
authors: Michael
authors: M
authors: Pratt
authors: Research Centre in Physical Activity, Health and Leisure, Faculty of Sport, University of Porto, Porto, Portugal.
authors: Carla
authors: C
authors: Moreira
authors: Research Centre of Anthropology and Health, Faculty of Sport Sciences and Physical Education, University of Coimbra, Coimbra, Portugal.
authors: Manuel João
authors: MJ
authors: Coelho-e-Silva
authors: Research Centre in Physical Activity, Health and Leisure, Faculty of Sport, University of Porto, Porto, Portugal.
authors: Susana
authors: S
authors: Vale
authors: Exercise and Health Laboratory, Faculty of Human Kinetics, Technical University of Lisbon, Lisbon, Portugal.
authors: Luis B
authors: LB
authors: Sardinha
mesh_terms: D000293:Adolescent; D002320:Cardiovascular Physiological Phenomena; D002648:Child; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010809:Physical Fitness / Q000502:physiology*; D012143:Respiratory Physiological Phenomena; D057185:Sedentary Behavior
keywords: Aerobic fitness/Vo2 Max