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Tuesday, March 5, 2013

An hour of exercise won't save you from the perils of sitting

Almost three years ago, I wrote that sitting can kill you. You may have been hoping that the damage done by sitting could be offset by doing some strenuous exercise everyday. I’m afraid not. A new study by Bernard Duvivier and his colleagues from Maastricht University Medical Centre shows that even an hour of vigorous exercise can’t compensate for spending the rest of the day in a chair.

The researchers recruited 18 volunteers to participate in three movement regimens, each lasting four days. In random order, people were asked to sit for fourteen hours/day (sitting), to sit for thirteen hours per day but vigorously pedal a stationary bike for one hour each day (exercise), or to walk for four hours and stand for two hours (minimal intensity). The last two protocols resulted in the same daily energy expenditure. After completing each four-day cycle, the subjects took a ten-day break before moving on to the next regime.

All participants spent the entire four days of each phase hooked up to monitors that measured both their energy expenditure and whether they were sitting, lying, standing or active. They were also asked to keep a food diary and to consume the same number of calories during each movement protocol, though their choices were not otherwise restricted. Finally, the volunteers were given stopwatches to remind them to record time spent sitting, standing or walking at fifteen minute intervals.

You can see the breakdown of the time spent on each activity below:

Figure 1 Time spent on different activities per regime.

Graphical overview of time spent in different activity categories (sleeping, sitting, standing, cycling and walking) in the three regimes followed by the participants.

On the morning of day five, after completing each four-day activity protocol, fasting blood samples were taken from each participant. Insulin and plasma lipid levels (cholesterol and triglycerides) did not differ between the sitting and exercise regimes. In contrast, levels of these molecules were improved after the minimal intensity protocol. The differences were not great, but consistent and could have implications for people hoping to stave off type II diabetes or cardiovascular disease.

To be clear, these data do not compare the benefits of vigorous versus low-intensity exercise. Rather, the experiments highlight the health differences between more sitting and less sitting. As expected, less sitting is better. More to the point, one hour of intense exercise per day does not change one’s blood profile. If you want to avoid the detriments of sitting, you’ll have to spend a large part of the day on your feet.

Duvivier, B., Schaper, N., Bremers, M., van Crombrugge, G., Menheere, P., Kars, M., & Savelberg, H. (2013). Minimal Intensity Physical Activity (Standing and Walking) of Longer Duration Improves Insulin Action and Plasma Lipids More than Shorter Periods of Moderate to Vigorous Exercise (Cycling) in Sedentary Subjects When Energy Expenditure Is Comparable PLoS ONE, 8 (2) DOI: 10.1371/journal.pone.0055542.