The Composition of a Child's Physical Activity and Their Cardio-Metabolic Health
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Purpose: The purposes of this study of 10-13 year old children were to: (1) determine if time spent in different domains of physical activity was independently associated with selected cardio-metabolic risk factors, and (2) estimate whether replacing time in one domain of physical activity with time in another domain of physical activity was associated with changes in cardio-metabolic risk factors. Methods: 385 children aged 10-13 years were studied. Participants wore a Garmin Forerunner 220 GPS watch, an Actical accelerometer, and completed an activity log for 7 consecutive days during the school year. Data from these measures was used to estimate average minutes/day spent in active transportation, outdoor active play, organized sport, and curriculum-based physical activity at school. Percent body fat, resting heart rate, and systolic blood pressure were measured using automated equipment. Isotemporal substitution regression models were used to estimate changes in cardio-metabolic risk factors that occurred when time spent in each domain of physical activity was replaced with an equivalent amount of time in another domain. Results: After adjusting for covariates, outdoor active play was associated with body fat % (β = -.058, 95% CI = -.095, -.021) and organized sport was associated with resting heart rate (β = -.040, 95% CI = -.071, -.009). In the isotemporal substitution models, replacing 10 minutes/day of organized sport with outdoor active play was favourably associated with body fat % (β = -.048, 95% CI = -.094 to -.002) and replacing 10 minutes/day of active transportation with organized sport was favourably associated with resting heart rate (β = -.109, 95% CI = -.197, -.020). Conclusion: These findings suggest that replacing time spent in organized sport with an equal amount of time in active play may have beneficial effects on body fat and that replacing time spent in active transportation with an equal time in organized sport may improve resting heart rate. No significant effects were observed when curriculum-based physical activity was replaced by another domain of activity.