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Born to be rich, physically active, fit and healthy?

There is accumulating evidence that physical activity provides important health benefits for children and adolescents. This conclusion is mostly based on the findings of observational studies and to some extent those of intervention studies. The documented health benefits include increased physical fitness (both cardiorespiratory fitness and muscular strength), reduced body fatness, favorable cardiovascular and metabolic disease risk profiles, enhanced bone health, and reduced symptoms of depression and anxiety (Physical Activity Guidelines Advisory Committee, 2008). The literature review by Stalsberg and Pedersen (2010) in this issue supports the hypothesis that adolescents with higher socioeconomic status (SES) are more physically active than those with lower SES. This association has earlier been shown among adults. With this in mind, special emphasis has to be laid on correct interpretation of the research on the sport–health relationship. Many health habits, such as smoking and diet, are differently distributed by both physical activity status and SES, which makes it difficult to establish cause–effect relationships between activity and future disease based on observational studies only. Also, genetic selection may play a hitherto underestimated role in the sense that individuals who participate in vigorous sports are a selected group with respect not only to physical fitness but also many other risk factors and morbidity (Kujala et al., 2003). The interesting association between high inherited aerobic fitness and low cardiovascular risk factor levels has also been shown in animal models (Wisløff et al., 2005).