Tracking of physical fitness levels from childhood and adolescence to adulthood: a systematic review and meta-analysis

Background: Prospective and large studies indicate that high physical fitness levels during young are beneficial for health during adulthood. The aim of the study was to investigate the tracking of physical fitness components from childhood and/or adolescence to adulthood. Methods: Two authors systematically searched MEDLINE and Web of Science electronic databases for relevant articles. Studies with apparently healthy youth aged 6-18 years who track their physical fitness to adulthood were included. Our study carried out according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Correlation coefficients (r) were used as effect size. Random-effects models were used to estimate the pooled effect size. Correlation coefficients were interpreted as follows: <0.30 low stability, 0.30 to 0.60 moderate stability, and >0.60 high stability. Risk of bias of each study was determined by The Quality Assessment Tool for Observational Cohort and Cross-sectional Studies. Results: Twenty-one prospective studies were included in the meta-analysis (n=6,197 participants at follow-up, 47.4% women). The mean length of follow-up was 20.8 years. Overall, cardiorespiratory fitness (r=0.38; 95% CI: 0.29-0.48; I2=92.7%), muscular strength (r=0.51; 95% CI: 0.43-0.59; I2=87.9%), and muscular endurance (r=0.50; 95% CI: 0.36-0.86; I2=94.5%) show moderate tracking from childhood and/ or adolescence to adulthood, independent of test used and length of follow-up. This moderate tracking was slightly stronger in women than in men and from adolescence compared to childhood. Trunk flexibility component, assessed with the sit and reach test, exhibits high stability (r=0.69; 95% CI: 0.58-0.81; I-2=92.9%). Interestingly, meta-regression analysis shows positive association between correlation coefficient for flexibility and the length of follow-up (beta =0.017; 95% CI: 0.012-0.021). Discussion: Although the current study found inconsistency between results, the findings suggest that acquiring high physical fitness levels should be targeted already from childhood and adolescence given that low levels of fitness in adulthood are related with several chronic diseases and mortality.