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MCMURRAY, R. G., J. S. HARRELL, S. I. BANGDIWALA and J. HU. Tracking of Physical Activity and Aerobic Power from Childhood through Adolescence. Med. Sci. Sports Exerc., Vol. 35, No. 11, pp. 1914–1922, 2003.To evaluate the tracking of physical activity levels (PA) and aerobic power (V̇O2max) in African-American (AA) and Caucasian (CA) youth as they age from 8 to 16 yr.Subjects were 529 girls and 535 boys for whom data were obtained at least three times over 7 yr and a subset of 387 girls and 404 boys who participated in all years. PA levels were obtained from a survey. V̇O2max was predicted from a cycle ergometer test.Spearman correlation for V̇O2max for years 1–7 for AA boys and girls were similar (ρ ∼ 0.53). Year 1–7 correlations for V̇O2max for the CA boys and girls were similar (ρ ∼ 0.50–0.53). The year 2–7 correlations for PA were similar for the AA and CA girls but higher for the AA than the CA boys. The kappa (κ) statistics for V̇O2max indicated substantial year-to-year agreement on categorization (high, moderate, and low), with AA girls having the highest agreement and AA boys the lowest. The κ statistic for high, moderate, and low PA groupings in girls of either ethnicity was quite low, whereas the κ statistics for the boys were somewhat better. The general estimating equation (GEE) stability coefficients for tracking of V̇O2max were similar between the sexes and ethnicities (P < 0.0001). The GEE stability coefficient for PA was better for the boys than girls and slightly better for the AA than CA.Although aerobic power and physical activity levels decline from childhood through adolescence, aerobic power tracks better than physical activity levels. Because tracking within the cohort is only moderate, change is possible if we intervene early in these youth.