Stability in physical activity levels in young adolescents

Abstract

There is a need for a descriptive epidemiology of stability and change in physical activity levels through childhood and adolescent years. The purpose of this study was to assess tracking (degree of stability) of 4 broad categories of self-reported physical activities in a sample of young adolescents over a period of 2 years. A representative sample of seventh graders (n=861) (478 boys and 383 girls, mean age at baseline 13.3 ± 0.3 years) in Hordaland county of Western Norway was first examined in 1990 and then again 2 years later in 1992. Both genders significantly reduced most activities while remaining stable in overall leisure-time physical activity as measured in hours per week. A substantial proportion of the sample, 69–90%, reported no or small deviations in the second year compared to baseline reports. Pearson's γ coefficients between corresponding measures at baseline and the second year were weak to moderate, varying between 0.25 and 0.51. Thus, the results do not indicate a conclusive pattern of tracking of physical activity. Mean levels were higher for boys than for girls at both time points on most measures. The data indicate that young adolescents become less physically active and their physical activity occurs in longer sessions. Further, a polarization between active and less active students seems to take place as the associations between the various measures were consistently stronger in the second year compared to the baseline year. This may reflect the beginning of a process leading to the existing polarization between the physically active and inactive sections of the adult population.