Fitness Mediates Activity and Sedentary Patterns Associations with Adiposity in Youth

Purpose We aimed to examine the cross-sectional associations of patterns of sedentary time (ST) and moderate-to-vigorous physical activity (MVPA) with total fat mass index (FMI) and abdominal fat mass index (FMIabd) in children, and additionally, to analyze if cardiorespiratory fitness (CRF) mediated these associations. Methods FMI and FMIabd were assessed with DXA in 333 participants (172 girls) aged 9-11 years. MVPA, ST, breaks in sedentary time per sedentary hour (BST/ST) and the number of daily sedentary bouts with various lengths (1-4, 5-9, 10-14, and ≥15 minutes) were assessed with accelerometry and CRF using a maximal cycle test. Hayes' PROCESS macro for SPSS was used for mediation analysis. Results The number of shorter sedentary bouts (1-4 minutes) was inversely associated with FMI (β =-0.108), whereas longer sedentary bouts (5-9 minutes, β=0.169; 10-14 minutes, β=0.193; ≥15 minutes, β=0.377) had a positive association, independent of MVPA (p0.05). CRF was inversely related to total and abdominal adiposity, and a large portion (40.9-65.7%) of the associations of MVPA and sedentary bouts with both FMI and FMIabd were mediated by CRF. Conclusion Time in MVPA and accumulating ST in shorter sedentary bouts is inversely related to adiposity. However, these associations may be mediated by CRF. Emphasis should be given to programs that target increases in MVPA, which may influence CRF while reducing sedentary recreational behaviors. Correspondence: Luís B. Sardinha, PhD, Exercise and Health Laboratory, Interdisciplinary Center for the Study of Human Performance, Faculty of Human Kinetics–University of Lisbon; Estrada da Costa, 1499-002 Cruz-Quebrada, Portugal, Phone: (351) 21 414 91 60; Fax: (351) 21 414 91 93; e-mail: lsardinha@fmh.ulisboa.pt This work was supported by the Portuguese Foundation for Science and Technology (Grant: PTDC/DES/108372/2008). DAS, JPM, and PBJ are supported by a scholarship from the Portuguese Foundation for Science and Technology (grants - DAS SFRH/BPD/92462/2013; JPM: SFRH/BD/85742/2012; PBJ: SFRH/BPD/115977/2016). Conflict of Interest The authors declare that they have no conflict of interest. The results of the present study do not constitute endorsement by ACSM and are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. Accepted for Publication: 11 September 2018. © 2018 American College of Sports Medicine

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