Agreed. We're back in cause vs. correlation territory, no? The most sedentary people may also be the most obese, the most likely to suffer from diabetes, the m

Agreed. We're back in cause vs. correlation territory, no? The most sedentary people may also be the most obese, the most likely to suffer from diabetes, the most burdened with respiratory and cardiovascular diseases, etc. Their expected lifespans will thus be quite shorter. I'm willing to believe that appropriate exercise is good for you, almost no matter how robust or frail your health is. But this would be a much better study if it tracked cohorts with roughly parallel starting health. That way, the degree of active-vs.-sedentary living could be a study variable that wasn't tainted by undocumented variations in starting health status.