RESEARCH PAPER Cardiorespiratory fitness and TV viewing in relation to metabolic risk factors in Portuguese adolescents Jorge Mota 1 , Rute Santos 1,2 , Carla Moreira 1 , Clarice Martins 1,2 , Anelise Gaya 1 , Maria Paula Santos 1 , Jose ´ Carlos Ribeiro 1 & Susana Vale 1 1 Research Centre in Physical Activity, Health and Leisure, Faculty of Sport, University of Porto, Portugal, and 2 Instituto Superior da Maia (ISMAI), Portugal Background: The purpose of this study was to examine whether adolescents who have high levels of cardiorespiratory fitness (CRF) co-existing with low levels of television (TV) viewing present a better metabolic risk profile compared to their low fit and high TV viewing counterparts. Subjects and methods: A total of 372 students (aged 12–15 years old) comprised the sample of this study. Anthropometric data (body mass index and waist circumference) was collected. CRF was calculated based upon the 20 metres shuttle run test. A questionnaire was used to estimate weekly TV viewing. Information about biological maturity and parental education was collected. Participants were then categorized into one of four category profiles according to the scores they achieved: low TV-Fit; high TV-Fit; low TV-Unfit and high TV-Unfit. Metabolic risk score (MRS) was calculated based on the sum of the Z-scores of all the metabolic variables analysed. Results: Logistic regression analyses indicated that the high TV-Unfit group was almost 3-times more likely to be assigned to the high MRS group (OR ¼ 2.85, 95% CI ¼ 1.08 – 7.50) compared to their low TV-Fit group counterparts. Conclusions: The data showed that the high TV-Unfit group was associated with an increased metabolic risk in adolescents after adjustment for gender, age, biological maturity and parental education. Keywords: Fitness, adolescents, TV viewing INTRODUCTION The prevalence of paediatric obesity has increased significantly in recent decades in Portugal (Sardinha et al. 2011; Carreira et al. 2012) as well as in most other countries (Wang and Lobstein 2006). Adolescence is a critical time because it is associated with changes in some behaviours such as a decrease in physical activity (PA), increased energy intake and increased sedentary time such as watching television (TV) and may all contribute to the development and establishment of overweight among youngsters (Dennison et al. 2002; Faith et al. 2003; Mikkila et al. 2005). Although watching TV it is not a direct measure of sedentary behaviour (SB), TV has been described as one type of SB that may increase obesity risk by decreasing energy expenditure (Reilly et al. 2005) or increasing energy intake (Epstein et al. 2008). However, a meta-analysis showed that associations between TV viewing and childhood obesity was weak and unlikely to be clinically relevant (Marshall et al. 2004). Moreover, some recent studies have shown that prolonged TV viewing was associated with increased risk of type 2 diabetes, cardiovascular disease (CVD) and all-cause mortality (Grontved et al. 2011). On the other hand, low levels of cardiorespiratory fitness (CRF) have been associated with the development of CVD risk factors in youth, such as lipid disorders, high blood pressure and insulin resistance among others (Ortega et al. 2008). Additionally, some data have pointed out that adolescents’ fitness and especially CRF have been decreasing over time (Dollman et al. 1999; Martins et al. 2008). Despite both TV viewing (Grontved et al. 2011) and CRF (Rizzo et al. 2007) having been associated with increasing risk of CVD and metabolic markers in adolescents, few studies have measured the association of both, i.e. the relationship established between the use of screen time/ sedentary behaviour (high vs low exposure) along with CRF (high vs low). Indeed, to the best of our knowledge few studies have addressed the co-existence of high/low TV time and high/low CRF and its relationship with metabolic risk profile of youngsters. Therefore, the purpose of this study was to examine whether adolescents with high levels of CRF and low levels of TV viewing have a better metabolic risk profile compared to their low fit and high TV viewing counterparts. Correspondence: Susana Vale, FADEUP, Research Centre in Physical Activity, Leisure and Health, R. Pla ´cido Costa, 91, 4200 450, Porto, Portugal. Tel: 351-22-5074786. Fax: 351-22-5500689. E-mail: susanavale@hotmail.com (Received 19 April 2012; revised 19 October 2012; accepted 12 November 2012) Annals of Human Biology, March – April 2013; 40(2): 157–162 Copyright q Informa UK, Ltd. ISSN 0301-4460 print/ISSN 1464-5033 online DOI: 10.3109/03014460.2012.752524 157 Ann Hum Biol Downloaded from informahealthcare.com by Michigan University on 04/02/13 For personal use only.