Search

The present thesis has investigated the cross-sectional and prospective associations between self-reported and objectively measured physical activity with five objectively measured indices of body composition in Norwegian adolescents participating in the Tromsø Study Fit: Futures Cohort. The three included papers used regression analyses to assess the cross-sectional association between self-reported physical activity and body composition in first year of upper secondary high school, and whether self-reported or objectively measured physical activity predicted changes in body composition between first- and last year of upper secondary high school. A significant cross sectional association was observed between self-reported physical activity and waist circumference (girls only), fat- and lean mass index for both sexes, but self-reported physical activity generally did not predict changes to body composition between baseline- and follow-up. Changes in level of physical activity during follow-up was predictive of changes in fat mass index in boys and lean mass index in girls. Objectively measured physical activity at baseline did not predict changes in body composition in boys, whereas time spent in sedentary- and light intensity predicted changes in indices of lean mass in girls. No association was observed with BMI in either of the included papers. The findings are interpreted in light of the substantial changes that occur in both habits and body composition during adolescence, and shows that there are health benefits of remaining- or becoming physically active during this period.

Objectives: To determine the mean body mass index (BMI, kg/m2 ) and prevalence of low weight (BMI

Objectives To determine the mean body mass index (BMI, kg/m2) and prevalence of low weight (BMI

Background: prevalence of obesity and overweight continues to increase in Norway, and more in young than old. This thesis has sought to describe the changes in BMI, with supplementary analyses of WC and WHtR, over a 13-year period. Furthermore, desired BMI (DBMI) has been analysed to assess whether the discrepancy between weight and desired weight is dependent on BMI categories of normal weight, overweight or obese. Methods and materials: The thesis has used data from the Tromsø Study, specifically surveys 4 (T4), 5 (T5) and 6 (T6). The material has been analysed both cross-sectionally and longitudinally, and so the population available for analyses depends upon participation in the different surveys. Results: The results show that BMI increased over the 13-year study period in both genders and all age groups but those aged 70-74 in T4. Increase was significantly associated with age at baseline, with a negative trend of BMI-increase with increasing age. A similar pattern applies for WC and WHtR. DBMI increased in all age groups of both genders, but the increase of DBMI was less than that of BMI during the period. Conclusion: Between T4 and T6, BMI increased in all age groups of both genders, an increase which is also evident in WC and WHtR. The analyses of BMI from the longitudinal cohort of T4, T5 and T6 indicate that the best part of the increase occurred between T4 and T5. The difference between BMI and DBMI is different between BMI categories, with normal weight people expressing low discrepancy between BMI and DBMI. The results confirm and extend previous knowledge on development of BMI in the Norwegian population.