You might recall a recent Australian study that put forward a correlation between time spent sitting and mortality rate, independent of other factors - i.e. the claim there being that if you sit a lot but exercise moderately then you have a lower life expectancy than if you spent less time in a chair. My thought at the time was that this sort of result ties back into levels of activity:

This is not the first study to propose this correlation, of course. There are a range of others from past years. One has to wonder what the mechanism is here, however - my suspicion is that it actually does all come back down to the level of physical activity in the end. In these massive studies the level of exercise and activity is reported by the participants. A person who stands and works is going to be somewhat more active than a person who sits and works, even though that time may not be categorized as physical activity, or reported differently.

Here is a different study that proposes much the same sort of thing. These researchers - like the authors of another recent study on Alzheimer's disease and activity - used data gathered from worn accelerometer devices rather than the self-reporting of study participants, which in theory should lead to far more confidence in the results.

Association of Sedentary Time with Mortality Independent of Moderate to Vigorous Physical Activity:

Low physical activity levels are a well-known risk factor of mortality. Previous studies have shown that people who do not meet the physical activity recommendations or those who report less moderate to vigorous activity (MVPA) are at increased risk of death. Sedentary behavior has emerged as a potential risk factor independent of MVPA and is defined as engaging in behaviors during the waking day that are done while sitting or reclining and that result in little energy expenditure above rest, such as using the computer, watching television, driving a car, or sitting at a desk.

Recent studies with objectively measured sedentary time data have shown that prolonged time in sedentary behaviors is a cardiometabolic risk factor independent of moderate to vigorous physical activity. Additionally, self-reported sedentary time in several domains including sitting, riding in a car, and TV watching is positively associated with mortality.

...

7-day accelerometry data of 1906 participants aged 50 and over from the U.S. nationally representative National Health and Nutrition Examination Survey (NHANES) 2003-2004 were analyzed. All-cause mortality was assessed from the date of examination through December 31, 2006.

...

This study shows that time spent in sedentary behavior is positively associated with mortality in this representative sample of adults aged 50 and older. Participants in the highest quartile of percentage of time spent sedentary, which corresponds to more than 73.5% of time in men and more than 70.5% in women, had more than 5 times greater risk of death compared to those in the lowest quartile. Importantly, these associations were independent of MVPA.

At some point in the future we won't really have to worry too much about things like this, as medical science will progress to the point at which maintenance of long-term health regardless of lifestyle becomes as much a non-issue as protection from the infectious diseases that plagued our ancestors. But we have a way to go towards that goal, and in the meanwhile it doesn't seem wise to sit back and assume that biotechnology will rescue you from casual negligence. Maybe you'll get lucky, but for those of us in the middle stages of life it looks uncertain indeed. The coming decades are on the cusp between the era of aging as a fact of life and aging as a treatable and reversible medical condition - a lot of deaths will fall on the wrong side of that line, so why not try to shift the odds on whether yours is one of them? Every year gained is big deal in this sort of situation.

The flip side of that coin is, of course, helping to make rejuvenation biotechnology come about more rapidly. If you like being alive and in good shape, it makes sense to work on both (a) common sense health basics like exercise and calorie restriction, and (b) assisting scientific progress. You live in an age in which you can easily accomplish both of these things, thanks to a wealth of health knowledge at your fingertips, and the spread of volunteer, philanthropically funded organizations like SENS Foundation and Methuselah Foundation.

Source:
http://www.longevitymeme.org/newsletter/latest_rss_feed.cfm