There was an interesting article in the New York Times on the effect of our genes on exercise. The study looked at the habits of approximately 37,000 twins to determine if there is a genetic link to exercising.
According to the findings, "Using complicated statistical formulas, the scientists concluded that differences in exercise behavior were about 60 percent attributable to genes. In other words, your parents influence your decision about whether to be active, not just by signing you up for soccer camp when you’re a kid but also by bequeathing you a genetic urge to work out — or not."
Read the article, Do Our Genes Influence Our Desire to Exercise?