Background: Regular physical activity is important for remaining healthy. Most studies on the association between active child- and adulthood were based on small non-representative populations. The purpose of the study was to quantify tracking of leisure-time PA (in and outside sports clubs) for 6 years from adolescence into young adulthood in a representative sample in Germany.
Methods: This study was a subsample of the "Motorik-Modul (MoMo) Longitudinal Study" (baseline: 2003-2006, wave 1: 2009-2012). Representative longitudinal physical activity data of N = 947 adolescents were included and collected using the MoMo-physical activity questionnaire (MoMo-PAQ). Stability of different physical activity indices was measured using Spearman's rank-order correlations and ANOVA with repeated measurement with age, sex and socio-economic status (SES) as determinants.
Results: While mean leisure-time physical activity outside sports clubs (LTPA) (F(1,397) = 7.9, df = 1; p < .01), sports club physical activity (SCPA) (F(387) = 4.8, df = 1; p < .05) and overall physical activity (OPA) (F(1,441) = 7.7, df = 1; p < .01) changed significantly over time, no changes in overall sports index (OS index) (F(371) = 3.2, df = 1; p > .05) were observed. Low tracking correlations were found for different physical activity indices (LTPA: r = .094, p < .05; SCPA: r = .248 p = <.05; OPA: r = .211 p < .05; OS index: r = .266 p < .05). Results by sex, age and SES were inconsistent. Analyses of agreement showed different results for determinants and settings.
Conclusion: The results of this representative study were comparable to previous studies and showed significant but low stability. Possible reasons for low stability coefficients are a relatively long timespan between both measurement points and potential effects of the reliability of subjective assessment methods. The results confirm that physical activity is a fluctuating variable. Future studies should examine the determinants of tracking and change in physical activity.