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‘My idea of exercise is a good brisk sit.’ Phyllis Diller

What is Sedentary Behaviour

Sedentary behaviour is any time spent primarily sitting or lying down and which involves expenditure of 1.5 metabolic equivalents (METs) or less (one MET is the amount of energy expended when doing absolutely nothing).
Examples of sedentary behaviour (calling it sedentary activity sounds like an oxymoron) are sitting, watching television, playing video games, and using a computer. Too much sitting, however, is distinct from too little exercise. Just sitting about is dangerous in its own right even if you do take enough exercise. For adults who meet the minimal public health recommendations on physical activity on most days each week, the 9–10 hours of sitting that can occupy their remaining, ‘non-exercise’, time can still have a damaging effect on their health. A new physical-activity grouping known as ‘active couch potatoes’ has emerged: those who apparently take the recommended amount of exercise but spend excess time just sitting around.

How much sitting about do we do?

The 2008 Health Survey for England (HSE) survey reported that around 40 per cent of adults spend 6 hours or more per day sitting down at weekends and slightly fewer on weekdays. A more recent assessment of sedentary behaviour comes from the HSE 2016.The self-reported average daily sitting time was 5.3 hours for men and 4.9 hours for women at weekends and 4.8 hours for men and 4.6 for women on weekdays. In each case, about 3 hours per day was spent watching TV. The trend was for more sedentary behaviour among the young (16–24 years), with an average sedentary time of 7 hours per day, and the old (70–79), at 9 hours per day – the so-called U-shaped curve.

The figures from the US are similar. A national study of nearly 6,000 adults in 2015/16 found that 26 per cent sat for more than 8 hours per day, with 45 per cent not getting any moderate or vigorous exercise, and about 11 per cent sitting for more than 8 hours and being completely physically inactive. Things may have got worse for young people with the huge growth in smartphone use. Among university students there is a direct relationship between time spent on the phone and decreasing levels of physical fitness.

The effect of the Lockdown

For the same age group, the influence of the Covid lockdown has produced some unexpected effects. In a study of 400 US college students, those participants who were not highly active before the pandemic actually increased physical activity after the closure of campus and the transition to remote learning. The participants who were highly active before the pandemic, however, experienced a decrease in overall physical activity. Weird!

Some other factors

Older people were also considered by the SITLESS study, which examined the sedentary behaviour of 1,360 community-dwelling elderly adults, average age 75. It reported that 79 per cent of waking time was spent sitting, 18.6 per cent in light activity and just 2.6 per cent in moderately vigorous activity. Watching TV and reading accounted for 47 per cent of waking time. 

There are clear occupational variations in sedentary behaviour, with office workers, as expected, spending more time sitting than blue-collar workers, though office workers do partly compensate for this risk by taking more leisure-time moderate and vigorous exercise than manual workers.

Next week I will look at the ill effects of too much sedentary time – and what we can do about it.

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