Physical Activity, Sedentary Time and Cardiovascular Fitness in Children: Are Bouts of Physical Activity Important?

Background: Cardiovascular fitness (CVF) is a key determinant of health; however it is unclear what patterns of physical activity (PA) contribute to healthy levels of fitness in children. Therefore, we evaluated how patterns of PA and sedentary time are associated with CVF in school-aged children.

Methods: Children (n=366, 8-11 yr) were participants in a whole school-based PA model (Action Schools! BC). We measured CVF (20-m shuttle run) and PA/sedentary time (Actigraph GT1M; 15-s epoch; three, 10-hr days). Using age-specific cutpoints, we calculated sedentary (<1.5 METs), light (1.5-2.9 METs), moderate-to-vigorous (≥ 3.0 METs; MVPA) and vigorous (≥ 6.0 METs) activity (min/day). We also derived MVPA/day accumulated in bouts of 0-5, 5-10, 10-20 and ≥20 min. We developed hierarchical regression models to assess the contribution of PA/sedentary time to CVF controlling for age, BMI and sex. To evaluate the independent contribution of bouted MVPA we included total and bouted MVPA in regression models.

Results: Age, BMI, and sex explained 9-13% of the variance in CVF. PA/sedentary time explained an additional 2-6% of variance (except for light PA). Bouted MVPA was not associated with CVF independent of total MVPA. Few children accrued MVPA in bouts ≥20 min. However, participants who achieved even one ≥20 min bout of MVPA were more fit (+5.8 laps) than those who accrued all MVPA in bouts < 20 min.

Conclusion: Bouted MVPA was not associated with CVF beyond that of total MVPA. However even one longer bout (>20 min) of MVPA may be important and warrants further study.