Objective: To analyse the secular trends in aerobic fitness and its determinants (BMI and leisure physical activity) in adolescents.
Design: Cross-sectional population-based studies in 1976 and 2001.
Participants: A stratified random sample of Finnish 13- to18-year-old pupils was studied in 1976 (N= 717; 384 boys and 333 girls) and in 2001 (N=558; 305 boys and 253 girls).
Main outcome measures: Aerobic fitness was measured with a 2000 m (for boys) and 1500 m (for girls) running test and participants’ weight and height were measured. Self-reported weekly frequency of leisure time physical activity of at least 30 min duration and regularity of participation in organized sport were obtained by questionnaire. Identical methods were used in 1976 and 2001.
Results:Running time was longer in 1976 compared to 2001 in both boys (56 sec; p<.001) and girls (29 sec; p<.001). In the linear regression analysis BMI and participation in leisure time physical activity explained more of the variance in aerobic fitness in 2001 than in 1976 in both boys and girls.
Conclusions: Aerobic fitness of school-aged children deteriorated between the measurement points. BMI and organized leisure time physical activity explained aerobic fitness better in 2001 than in 1976. An increase in overweight and obesity was associated with the decrease in aerobic fitness. Although the importance of organized leisure-time physical activity to fitness increased, it is possible that the decrease in overall physical activity between 1976 and 2001 contributed most to the decrease in the level of aerobic fitness.