Working in a safe and healthy way 

With the Guidelines for Exercising (August, 2017) the Dutch Board of Health paid attention to the health risks associated with sitting for prolonged periods for the first time. This was badly needed because more and more studies show that the health risks associated with sitting for prolonged periods are substantial. Unfortunately in practice these guidelines don't offer much help.

What exactly is the limit to sitting for prolonged periods?

The guidelines are very specific about the right amount of exercise people need: "at least 150 minutes of moderate intensity like walking or cycling, spread across various days." But the guidelines regarding sitting for prolonged periods of time are very sketchy, just "avoid being seated all the time"

This of course is very vague because how does one define 'a lot' and for how many hours you may keep seated? Luckily two recent international studies are here to guide us.

The American guidelines are more specific than their Dutch counterparts 

Since 2018 there's also new Guidelines for Exercising in the United States. As to sitting for prolonged periods of time these guidelines are more specific than their Dutch counterparts. The guidelines state that sitting and physical activities are related in terms of their impact on people's health (the mortality rate). This is based on a review article written by professor Ekelund and his colleagues back in 2016. The American committee has developed a so-called heat map on the basis of the findings of professor Ekelund and co.

Have a look at the graph. If you don't sit that often (bottom of the graph) you don't need that much physical activity and you're in the clear (green means a low risk for mortality). If however you're seated almost all day long (top of the graph), you need a whole load of physical activity to get and stay healthy and lower your risk for mortality. The Dutch Guidelines for Exercising (2017) don't distinguish between little or a lot hours of exercise. In there the sketchy explanation "Avoid being seated all the time" applies to everyone.

Figure: the relationship between the amount of moderate to intensive physical activity per week, the amount of time spent seating per day and the relative risk of untimely death (resource number 4). The numerical addition based on resource number 1 are arbitrary because of the absence of a graph scale.

What is the limit value to sitting for prolonged periods?

You should keep in mind that a total of 150 minutes of exercise per week isn't enough to compensate for eight hours of sitting per day. Please note that the minimum recommended amount of physical activity in the United States is 150 minutes per week, same as THE NETHERLANDS, even for people who don't sit that long and often. This guideline has been added to the graph, just as the minimum recommended amount of physical activity for people who sit for prolonged periods of time and very often. This demonstrates 150 minutes of exercise per week isn't sufficient if at the same time you're seated eight hours or more per day.

The heat map is one of the tools you can use to get yourself or a colleague out of the woods and into the green. You can do this by exercising more and be seated less. Every form of physical activity, no matter how small reduces the risk for mortality, so go for it.

The limit value, a quantitative tool to prevent sitting for prolonged periods

The limit value can be used as a quantitive tool to prevent sitting for long periods of time. This tool has been taken from a new review article by professor Ekelund and e.a. dating from 2019. Same as in 2016 they've identified the relationship between being seated, physical activity and the risk for untimely death. This time however they solely included studies in which being seated and physical activity where measured with an accelerometer. This kind of measuring is way more accurate than to simply ask people how much time they're being seated or exercising. People are inclined to underestimate their seating time and overestimate the amount of exercise they get on a daily basis.

What does the data taken from 36.383 United States and Western Europe citizens say? 

According to data, taken from a total of 36.383 citizens of the United States and Western Europe, sitting for prolonged periodes of time is related to an increased risk for premature death. The data further shows that the risk for premature death increases along with the length of the sitting period. If the length of the sitting period transcends 9,5 hours a day the risk for premature death is significantly higher. Now there's a limit value to prolonged sitting periods for you.

A proposal to set the limit value to prolonged sedentary 

Limit your seating period to 9 hours a day (per 24 hour period) and preferably to 7,5 hours a day (1). Spend half of your waking hours (an average of 16 hours per day), so eight hours per day on standing, walking and exercising and try to alternate between these activities. At an eight-hour working day you need to spend a total of 4 hours on physical activity like the ones mentioned above and also alternate between those. You can also apply this 50-50 rule to a two-hour tv night: 1 hour of sitting down and 1 hour of standing and exercising. It's difficult to keep track of time and advisable to use an activity monitor to keep an eye on the time you've spent on sitting and exercising. The guidelines that has been set out can change at any time, due to new scientific evidence or new insights. In the mean time keep yourself healthy with a healthy diet and enough daily and weekly exercise. You'll be grateful to yourself.

Alternate between seated periods and periods of standing and exercising, the more intensive the better. There's not an unambiguous
guideline yet to the minimal required period of alternating between these activities.

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general workplace

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