Physical fitness and overweight in Swedish youths

Sammanfattning: The aim of the present thesis was to describe the level of physical fitness and prevalence of overweight and obesity in Swedish youths, and their trends over 14 years. Additionally, the relation between fitness and overweight on the one hand and physical activity on the other was examined. In 2001, a total of 2118 children, aged 10, 13 and 16 years, were invited from 48 randomly selected schools in Sweden. Out of these, 1732 or 81.8 % participated in the testing. For trend analyses, data collected in 1987 from a sample of 516 children were used. When subjects in the 2001 sample were analysed according to proposed cut-off values, 15.7% (95% CI: 14.1% to 17.6%) of all subjects were found to be overweight and 4.3% (95% CI: 3.4% to 5.4%) were obese. The total prevalence accordingly being 20.1% (95% CI: 18.3% to 22.0%). This sample proved to be heterogeneous concerning overweight status. When obesity and overweight were combined the highest prevalence (26.6%, 95% CI: 21.2 to 32.7) was found in 10-year-old girls and the lowest (17.5%, 95% CI: 13.6 to 22.2) in 16-year-old girls. The prevalence in 2001 was nearly 2.5 times higher, compared to the 1987-sample. Girls attending schools in smaller towns or on the countryside had a nearly two-fold prevalence of overweight and obesity, compared to girls living in the major cities. The difference was less pronounced in boys. The prevalence of overweight and obesity was related to level of physical activity in 10 and 13 years old children but not in 16 years old. Results from the performance tests in the 1987 and 2001 samples were compared. Concerning cardio-respiratory performance, girls aged 16 years showed only small differences, whereas boys in the 2001 sample performed worse compared to boys in the 1987-sample (46 ml x kg-1 x min-1 vs. 41 ml x kg-1 x min-1 for 1987 and 2001, respectively, and median difference 9.2 %, 95% CI: -16.7 to -2.2). Concerning neuro-muscular performance, the comparisons of results between the 1987 and 2001 samples showed varying results. Generally, performance on the upper body and trunk muscles strength and endurance tests was lower in 2001 compared to 1987. Neuromuscular performance in the lower body differed less. For both boys and girls, differences in neuro-muscular performance between subjects in different activity strata increased with age. Results showed only small differences in neuro-muscular performance between active and less active strata at age 10, but larger at age 13 and 16 years in both boys and girls. And at age 13 and 16 years, neuro-muscular performance differed widely between active and less active girls. At age 10, only small differences were found in cardio-respiratory performance between active and less active subjects (both girls and boys). At age 13 and 16 years both girls and boys showed large differences in cardio-respiratory performance between activity levels, with better performance in more active children.