Twin-sibling study and meta-analysis on the heritability of maximal oxygen consumption

Large individual differences exist in aerobic fitness in childhood and adolescence, but the relative contribution of genetic factors to this variation remains to be established. In a sample of adolescent twins and siblings (n = 479), heart rate (HR) and maximal oxygen uptake ((V) over doto(2max)) were recorded during the climax of a graded maximal exercise test. In addition, (V) over doto(2max) was predicted in two graded sub-maximal exercise tests on the cycle ergometer and the treadmill, using extrapolation of the HR/(V) over doto(2max) curve to the predicted HRmax. Heritability estimates for measured (V) over doto(2max) were 60% in ml/min and 55% for (V) over doto(2max) in ml.min(-1).kg(-1). Phenotypic correlations between measured (V) over doto(2max) and predicted (V) over doto(2max) from either submaximal treadmill or cycle ergometer tests were modest (0.57 < r < 0.70), in part because of the poor agreement between predicted and actual HRmax. The majority of this correlation was explained by genetic factors; therefore, the submaximal exercise tests still led to very comparable estimates of heritability of (V) over doto(2max). To arrive at a robust estimate for the heritability of (V) over doto(2max) in children to young adults, a sample size weighted meta-analysis was performed on all extant twin and sibling studies in this age range. Eight studies, including the current study, were meta-analyzed and resulted in a weighted heritability estimate of 59% (ml/min) and 72% (ml.min(-1).kg(-1)) for (V) over doto(2max). Taken together, the twin-sibling study and meta-analyses showed that from childhood to early adulthood genetic factors determine more than half of the individual differences in (V) over doto(2max).