Physical activity, cardiovascular fitness and abdominal adiposity in children and adolescents

• Cardiovascular fitness (CVF) and adiposity, especially abdominal adiposity, are well-known factors associated with general health status in childhood and adolescents. Physical activity (PA) may play a crucial role in CVF enhancement and the prevention of abdominal adiposity accumulation. The apparently obvious association of PA with CVF and adiposity still requires further research, since current knowledge is mostly based on data from self-reported measures but such measures are of limited use in pediatric populations. The current thesis aimed to examine the associations of objectively measured PA with CVF and abdominal adiposity in more than one thousand children (9-10 years) and adolescents (15-16 years) from the Swedish part of the European Youth Heart Study. Total PA levels and time spent in PA of different intensities (i.e. moderate and vigorous PA) were measured by accelerometry. Cardiovascular fitness was measured by a maximal cycling test. Body mass index was used to define overweight/obesity, and waist circumference to define an excess of central adiposity. Percentage body fat was estimated from skinfold thickness. Stages of sexual maturation were identified according to Tanner. The main findings and conclusions were: I) When examining CVF in adolescents, sexual maturation status and percentage body fat, as well as the way in which CVF is expressed, should be taken into account. II) Those adolescents who spend 60 minutes or more in moderate to vigorous PA daily seem to be more likely to have a healthier CVF level, independently of their sexual maturation and adiposity status. III) Low levels of total PA and, in particular, of vigorous PA, are associated with an increased risk for overweight and excess of central adiposity, independently of other important determinant factors, such as television viewing and birth weight. The data also indicate that the adverse association of television viewing with abdominal adiposity could be attenuated if sufficient vigorous PA is accumulated. IV) Cardiovascular fitness is inversely associated with abdominal adiposity and seems to modify the associations between PA and abdominal adiposity. In children and adolescents with low CVF, time spent in vigorous PA seems to be the key component linked to abdominal adiposity. The findings reported in this thesis will contribute to a better understanding of the associations of PA with CVF and abdominal adiposity, a prerequisite for more efficient health promotion. Future public health recommendations should consider the evidence-based importance of high intensity PA.

Nyckelord

Physical activity, accelerometry, fitness, aerobic capacity, adiposity, waist circumference, children, adolescents

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