CCL2 in lean and overweight/obese children according to aerobic fitness. Study participants (n = 36) were age, sex and maturity offset matched to lean controls. Fasting blood samples were analyzed for CCL2 (intra-assay CV = 6.2%). Aerobic fitness was measured using a continuous cycling test to exhaustion, with values expressed relative to fat-free mass. Group assignments were based on median split of aerobic fitness values in overweight/obese and lean children: overweight/obese, low fitness (OW-LF); overweight/obese, high fitness (OW-HF); lean, low fitness (L-LF); lean, high fitness (L-HF). A) Individual values of CCL2 B) Combined group values. Significant correlations (P-value <0.05) are marked for comparisons between obese children who have low fitness (OW-LF) and lean children who have low (L-LF) and high (L-HF) fitness levels.