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A summary of the evidence for a contribution of genetic variability to physical activity–related traits is presented. The availability of a reference human DNA sequence has made it possible to screen individuals and populations for the presence of genomic differences. Even though more than 100 million DNA variants have been identified, human beings share a genomic sequence, which is more than 99% identical. Four major lessons can be derived from ongoing genomic and genetic studies. First, the connection between a genotype and a phenotype is highly complex. Second, the expression of genes is regulated via multiple interacting mechanisms. Third, redundancy and compensatory mechanisms are ubiquitous. Fourth, complex, multifactorial traits are influenced by polygenic systems defined by hundreds and thousands of loci with most alleles characterized by very small effect sizes. The contribution of genetic variability is briefly summarized for human longevity, common chronic diseases, physical activity level, cardiorespiratory fitness in the sedentary state, and in response to exercise programs.

The relationship between habitual physical activity and pulmonary function were considered in 424 boys and 366 girls, 9–18 years of age. Indicators of habitual physical activity were assessed using a 3-day activity diary and included estimated daily energy expenditure (EE) and time spent in moderate-to-vigorous physical activity (MVPA) (METs ≥ 4.8). Pulmonary function was measured according to standard procedures. Relationships were examined with partial correlations and ANCOVA, comparing the highest and lowest quartiles of EE and MVPA. When age and stature are statistically controlled, relationships between EE, MVPA, and pulmonary function was generally low and not significant, with the exception of FEV₁% in 16–18-year-old girls (r ≤ −0.28). Youth in the highest and lowest quartiles of EE and MVPA do not differ in pulmonary function, except for PEER in 9–12-year-old boys, and FEV₁% in 16–18-year-old boys, which are slightly greater (1–3%) in the less active group. These findings indicate that lung volumes, capacities, and flow rates are not consistently related to estimated habitual physical activity in a general, free-living population of youth.