What is “Sedentary Behaviour”?
It sounds like an oxymoron – surely behaviour implies activity? Sedentary behaviour, however, is recognised and is defined as any time spent primarily sitting or lying down and which involves very low levels of energy expenditure. Examples are sitting, watching television, playing video games, and using a computer. Too much sitting must be seen as distinct from too little exercise. Just sitting about is dangerous in its own right even if you do take exercise. For adults who meet the minimal public health recommendations on physical activity on most days each week, there are still adverse metabolic consequences of the 9 to 10 hours of sitting that can occupy their remaining “non-exercise” time.
How much do Brits sit about?
The 2012 Health Survey for England (HSE) reported that around 40% of adults spend 6 hours or more per day sitting down at weekends and slightly fewer on weekdays. Average daily sitting time is 5.4 hours for men and 5.1 hours for women at weekends and 4.9 hours for men and 4.7 for women on weekdays. In each case about 3 hours per day is spent watching TV. The trend is for more sedentary behaviour among the young (16 to 24) with an average sedentary time of 7 hours/day, and the old (70 to 79) at 9 hours /day, the so-called U shaped curve.
What’s the damage?
Both total sedentary time per day and length of sedentary bouts are predictors of premature death and the combination of the two triples the risk of premature mortality. This has even received a label – “the sedentary death syndrome”. Also the more you sit about the higher your risk of developing cardiovascular disease and diabetes – independently of the amount of exercise you take when not sitting about.
The US experience – getting worse
A recent paper from the US has examined trends in sedentary behaviour from 2001 to 20161. The prevalence of computer use outside school or work for at least one hour/day increased from 43% to 50% for children, from 53% to 57% among adolescents and from 29% to 50% for adults. Total sitting time increased from 7.0 to 8.32 hours/day among adolescents and from 5.5 to 6.4 hours/day among adults.
What can we do?
A variety of measures have been proposed to get us to move about more, including a walk at lunchtime, pacing about when on the phone, taking the stairs not the lift, using a pedometer as a prompt to keep moving, active travel and getting off the bus one or two stops early. More unusual suggestions include standing at your desk, and the Stir Kinetic MI, a computerised desk which detects when its owner has been sitting for too long and moves up and down a few inches to force them to stand up!
The good news is that some of the harms of too much sofa time are alleviated by vigorous exercise – which has additional benefits and definitely trumps a bossy desk.