Longitudinal and cross-sectional associations between physical activity, screen time, and fitness in a sample of young children from Edmonton, Canada

  • Author / Creator
    Potter, Morgan R
  • Background: High fitness is associated with several positive health outcomes; however, fitness of Canadian children has declined over the past two decades. Correlates of fitness in children under 10 years of age are relatively unexplored, and few studies involving young children have looked at this relationship over time. Understanding these potential associations at young ages and over time is necessary to better understand how to increase fitness levels in children. The purpose of this thesis is to: (1) describe the fitness level of a large group of Canadian children; (2) examine the cross-sectional associations between physical activity (PA), screen time (ST), and fitness; (3) examine the longitudinal associations between PA, ST, and fitness; and (4) explore PA and ST tracking over three years. Methods: Findings are based on 649 participants (4.5 ± 0.5 years at baseline; 52.4% female) from Edmonton, Canada who participated in the Spatial Health Assessment of Physical Environments (SHAPEs) baseline study (2005-2007) and the SHAPEs of Things to Come three-year follow-up (2008-2011) study. Parent-reported questionnaires measured PA and ST in hours/week at both time points. At follow-up, PA was also objectively measured using pedometers. Fitness was measured using the Canadian PA, Fitness and Lifestyle Approach manual at follow-up only. Vertical jump, sit-and-reach, waist circumference, grip strength, and predicted VO₂ max were expressed as z-scores. Total fitness-complete (complete results for vertical jump, sit-and-reach, waist circumference, grip strength, and predicted VO₂¬ max) and fitness-partial (complete results for at least three of the measures included in fitness-complete) were averaged and expressed as z-scores. Due to non-normal distributions, push-ups and partial curl-ups were categorized into high (“gold-standard” for the Canada Fitness Award) and low groups. Linear or logistic regression was used to examine the cross-sectional and longitudinal associations, and models adjusted for follow-up age, sex, household income, and body mass index. Sex-interactions were explored. Spearman correlations were used to examine PA and ST tracking. Results: Children’s mean fitness scores were 39.4 ± 2.3 ml∙(kg∙min)⁻¹ for predicted VO2max, 30.8 ± 6.1 kg for grip strength, 20.4 ± 5.1 cm for vertical jump, 28.1 ± 6.6 cm for sit-and-reach, and 59.8 ± 6.0 cm for waist circumference. For push-ups and partial curl-ups, 20.5% and 7.9% of participants were categorized into the high fitness group, respectively. Cross-sectionally, some positive associations were observed between objective PA and fitness (fitness-complete: β=0.009, 95% CI: 0.001, 0.017; fitness-partial: β=0.006, 95% CI: 0.000, 0.011; vertical jump: β=0.043, 95% CI: 0.008, 0.078; boys VO₂ max: β=0.084, 95% CI: 0.012, 0.157 and; being in the high push-up group: OR=1.156 95%CI: 1.054, 1.267) and between subjective PA and fitness (fitness-partial: β=0.025, 95% CI: 0.007, 0.042; vertical jump: β=0.011, 95% CI: 0.000, 0.022; boys VO₂ max: β=0.040, 95% CI: 0.018, 0.063 and; boys grip strength: β=0.025, 95% CI: 0.011, 0.040). Negative associations were observed between fitness and ST for boys grip strength only (β=-0.016, 95% CI: -0.028, -0.004). Longitudinally, no significant associations between baseline PA and follow-up fitness scores were observed but two positive associations approached significance (p=0.05; fitness-complete: β=0.007, 95% CI: 0.000, 0.014; VO₂ max, β=0.014, 95% CI: 0.000, 0.027). Only two significant negative associations were observed between baseline ST and follow-up fitness (fitness complete: β=-0.009, 95% CI: -0.016, -0.002; grip strength: β=-0.010, 95% CI: -0.019, -0.001). Physical activity displayed moderate (rs=0.30), and ST displayed large (rs=0.53) tracking coefficients over three years. No sex-interactions were observed. Conclusions: This thesis adds valuable knowledge to the fitness literature by providing evidence on an important, yet understudied, group of children. For PA, significant or borderline significant associations were observed with overall fitness in both analyses. For ST, cross-sectional and longitudinal associations were observed with one musculoskeletal fitness score (grip strength) and longitudinal associations were observed with overall fitness. Overall, these findings suggest that targeting PA and ST may be important for overall fitness, especially because these behaviours track over time. Given the paucity of evidence in this age group and the small effects observed, additional research is needed to confirm these findings and determine the best ways to intervene.

  • Subjects / Keywords
  • Graduation date
    Fall 2016
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.