Everybody knows that doing exercise is good for you, right? Low fitness is highly correlated with all-cause mortality (death) and regular physical activity decreases the risk of all-cause mortality.
But what you perhaps didn’t know is that sedentary behaviour is a distinct class of behaviour [1]. It has specific determinants and effects on disease risk, independently increasing disease risk despite leisure time exercise, and increasing mortality and disease risk further in individuals with insufficient physical activity. One study showed that 6.9% of all-cause mortality was attributable to sitting [2].
Another study assessed the risk of prolonged sitting when it’s broken up by activity. What they found was that blood glucose and insulin levels were reduced with both light and moderate activity breaks compared to uninterrupted sitting. Benefits were gained with the walking break, regardless of the intensity of walking. Neither intensity showed more benefits than the other [3].
Watching television increased hazard ratio (risk) of all-cause mortality (death), even in those getting seven hours of exercise per week. This increased risk of all-cause mortality was equivalent to those who never exercised but never watched television. In other words, all the gains to your health achieved by doing more than seven hours of exercise a week, were cancelled out through watching more than 7 hours of television a week. Television has also been associated with eating the unhealthy foods and prolonged sitting [4].
The molecular and physiological responses in the human body from too much sitting are not necessarily reversed by an additional bout of physical exercise.
People already insufficiently physically active will increase their risk even further by prolonged sitting time.
Prolonged sitting has an impact of morbidity (illness) as well. Sedentary time is detrimentally associated with:
Waist circumference (how fat you are!)
HDL cholesterol (the good cholesterol)
C-Reactive protein (a measure of how much inflammation is in your body)
Triglycerides (another sort of blood fat)
Insulin (the hormone that moves sugar from your blood into your cells)
Beta cell function (where insulin is made in the pancreas)
Insulin sensitivity (how well your insulin works)
So the solution is to integrate modest amounts of physical activity throughout the day to reduce sedentary behaviour. Get creative: stand-up or treadmill desks might be an option. Sustained pulses of low-grade activity are going to have more of an impact on metabolic parameters (things like your sugar, insulin level, blood pressure, weight, etc) than a three-times-a-week visit to the gym. Let me just repeat that: You’ll get more health benefit by regular low-grade activity throughout the day, compared to a sedentary working week interspersed with alternate day, hour long visits to the gym. The bottom line: just get up every 20 minutes and move….
References:
Ekblom-Bak, E., M.L. Hellenius, and B. Ekblom, Are we facing a new paradigm of inactivity physiology? Br. J Sports Med, 2010. 44(12): p. 834-5
van der Ploeg, H.P., et al., Sitting time and all-cause mortality risk in 222 497 Australian adults. Archives of Internal Medicine, 2012. 172(6): p. 494-500.
Dustan, D.W., et al., Breaking up prolonged sitting reduces postprandial glucose and insulin responses. Diabetes Care, 2012. 35(5): p. 976-83.
Matthews, C.E., et al., Amount of time spent in sedentary behaviours and cause-specific mortality in US adults. Am J Cli Nutr, 2012. 95(2): p. 437-45.