Berntzen B, et al. – The objectives of this study were to evaluate how monozygotic (MZ) twin pairs who are discordant for body mass index (BMI) differ for objectively and subjectively measured physical activity (PA) and cardiorespiratory fitness (VO2max), and correlations of PA and VO2max with adiposity and measures of metabolic health, in individual twins and independent of genetic and shared environmental effects within twin pairs. It was revealed that objectively, but not subjectively measured PA is correlated with lower adiposity and better metabolic health, independent of genetic and shared environmental factors.