"Those who think they have not time for bodily exercise will sooner or later have to find time for illness." -- Edward Stanley, Earl of Derby 1873
We continue to deny this idea despite more than a century of data. In the latest contribution to this argument, an Australian group put another nail in the coffin of the couch potato. They demonstrated that the amount of time we spend sitting correlates with all-cause mortality. For those who haven't been living under a rock, this is not news. However, what puts this study on the map is the finding that the negative effect of prolonged sitting was not significantly reversed by physical activity.
The fact that modern humans spend so little time out of a chair has given birth to a vital new field, sedentary behavior research. Investigation has revealed that the adverse consequences of prolonged sitting (surely this will become a familiar acronym in the literature -- PS -- so let's coin it now) stem from a web of causes including: reduced metabolic function, increased triglycerides and decreased HDL-cholesterol (the good one), decreased insulin sensitivity, and impaired carbohydrate metabolism. These are the usual suspects in any discussion of cardiovascular disease, diabetes or obesity.
But now the data suggests two important things. First, it seems that physical activity and sedentary behavior act independently through different mechanisms. This would explain why the damage of PS (sitting for 11 hours a day) is not completely mitigated by 30 minutes of daily exercise. Secondly, they have found that normal weight is not fully protective against the ravishes of PS and in no way means you're healthy.
The pioneering work on this issue was done in the early 1950s by a British researcher, Dr. Jeremy Morris, the man responsible for connecting physical exertion and health. In seeking to determine whether there was an association between the type of work people do and heart disease, he stumbled upon groundbreaking data. Morris combed through the health records of 31,000 bus drivers and conductors in London. The conductors had significantly less heart disease than the drivers. The only variable that consistently distinguished one group from the other was activity level.
So if this link was appreciated more than 50 years ago, why has so little been done, allowing heart disease to remain the number one killer? The answer is simple. Medicine addresses disease, not health. Until you are sick, the medical system has had nothing to offer. We've gotten better at treating heart disease, but have just begun to seriously consider preventing it. Until people stop thinking about health in terms of doctors and medicines, things will not change.
The "progress" afforded by the Industrial Revolution has provided a natural experiment demonstrating the catastrophic effects of sedentary life. If one considers our genetic wiring, perfected over hundreds of thousands of generations, this all makes perfect sense. We were made to move. And our genome has not adapted to this relatively new lifestyle. It turns out we need more than exercise.
So don't just sit there. Get up and get well.
 Archives of Internal Medicine, March 26, 2012, van der Ploeg et al. 172 (6):494
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