The Relation between Aerobic Fitness, Muscular Fitness, and Obesity in Children from Three Countries at Different Stages of the Physical Activity Transition

Abstract

Background. The physical activity transition is contributing to an increase in childhood obesity and a decrease in fitness worldwide. This study compared body composition and fitness measures in children from three countries and examined intercountry differences in the relationship between these variables. Methods. Participants consisted of 736 Canadian, 193 Mexican, and 179 Kenyan children aged 9-13 years. Body mass index (BMI), waist circumference, triceps skinfolds, aerobic fitness, and muscular fitness were measured. Linear regression was used to examine associations between variables. Results. The prevalence of obesity was the highest in Mexican children (9.2% boys, 8.4% girls) and the lowest in Kenyan children (0.9% boys, 2.8% girls). Aerobic fitness (VO2max in mL/kg/min) was the highest in Kenyan children (50.2 boys, 46.7 girls) and the lowest in Canadian children (41.3 boys, 38.3 girls). Aerobic fitness was negatively associated with body composition measures irrespective of country and sex. Mexican children with low aerobic fitness had higher body composition measures than Canadian and Kenyan children. Muscular fitness was not associated with the body composition measures in Kenyan children but was a weak positive correlate of BMI and waist circumference in Canadian and Mexican children. Conclusion. The current study provides some evidence to support the physical activity transition hypothesis.

Figure 1

Association between aerobic fitness and body mass index (BMI) in boys (a) and girls (b) from Canada, Mexico, and Kenya. The data for each sex and country subgroup are plotted from 2 SD below the mean to 2 SD above the mean. The figure shows a negative association irrespective of sex and country. The figure also displays that the intercepts and slopes of the regression lines are greater in Mexican children than in Canadian and Kenyan children. Thus, for BMI, Mexican children with low aerobic fitness levels have higher body composition values than do Canadian and Kenyan children. However, body mass index values of children in all three countries are similar in those with high aerobic fitness levels.

Figure 2

Associations between muscular fitness (grip strength) and body mass index (BMI) in boys (a) and girls (b) from Canada, Mexico, and Kenya. The data for each sex and country subgroup are plotted from 2 SD below the mean to 2 SD above the mean. The figure shows that muscular fitness is positively associated with BMI in boys and girls from Mexico and Canada. The association is less pronounced and not statistically significant in Kenyan boys and girls.