The association between low physical fitness and high body mass index or waist circumference is increasing with age in children: the 'Quebec en Forme' Project

Objective: To evaluate physical fitness and body composition of children involved in the 'Quebec en Forme' (QEF) Project and to compare data obtained to the reference values of the 1981 Canada Fitness Survey (CFS). Design: Cross-sectional study. Subjects: A total of 1140 children (591 boys and 549 girls) of first (7 years), second (8 years) and fourth (10 years) grade from primary schools in the City of Trois-Rivie` res (Quebec) were selected to participate in this study. Measurements: Body mass index (BMI) and waist circumference (WC) were measured. The physical fitness tests included standing long jump, 1-min speed sit-ups and speed shuttle run. Results: The prevalence of overweight in children ranged between 20 and 30%, which represents a substantial increase compared to the 1981 CFS. The relationship between BMI and WC was highly significant in boys and girls (r = 0.90 and 0.86, respectively, P < 0.0001). The negative correlations between BMI or WC and the performance in all physical fitness tests were mostly significant in children of both genders (-0.16 <= r <= -0.45, at least P < 0.05), and these relationships were significantly greater in older children (P < 0.05). Based on the 1981 CFS, only 4.7-14.1% of QEF boys still performed in the upper quartile of the distribution (fit boys), whereas 32.1-69% performed not much higher than the lower quartile (unfit boys) for each fitness test. In girls, the relative fitness decrease observed in 2003 was more pronounced since only 1-9.9% of subjects performed in the upper quartile of the distribution compared to 42.8-81.4% who did not perform higher than the lower quartile of the 1981 reference scores of the CFS. Conclusion: This study shows that BMI and WC are negatively correlated with physical fitness and that these associations are more pronounced in older children. Furthermore, physical fitness of our cohort, especially in girls, was much lower than what was documented in the 1981 CFS in subjects of the same age. This study thus emphasizes the necessity to develop early interventions to improve physical fitness in children and to prevent the increase of childhood obesity.