23rd October, 2015
by Ergonomics Department
Fixed height office desks have been around since the conception of offices. Work practices, types of workers, our knowledge on ergonomics, and health & safety requirements have been changing continuously yet we still use fixed height desks. Our love affair with the fixed height desk goes on whilst in countries like Denmark, Sweden, Holland and to some extent Germany employers on the advice of Ergonomists have been specifying height adjustable desking for their employees. Studies from Scandinavian countries show that, since the introduction of height adjustable desking there has been a clear reduction in reported back pain and other musculoskeletal disorders. Is it now time for us to consider the use of height adjustable desks and promote alternating between sitting and standing during the course of work in an office environment? Here are some facts and myths about height adjustable desking.
There is confusion about what is meant by height adjustability of desks. In theory, a desk which can be set at different heights is deemed to be height adjustable. However, in terms of ergonomics and users’ point of view, true height adjustability means that users at any time can alter the height of their desks by themselves by means of crank mechanisms, gas springs or electric motors without the need of specialised tools and with minimal effort. This type of height adjustability is called ‘true user adjustability’ and such desks are referred to as ‘user adjustable desking’.
On the other hand, the simple height adjustability offered by many manufacturers is the ability to install desks at different heights (other than the fixed height of 720mm as specified in standards) as required by the purchasers or users. These usually involve mechanical adjustments to the desk leg components that require specialised tools and skilled personnel. In other words once it is set, it becomes a fixed height desk and cannot be adjusted again by the users. This type of adjustability is called ‘adjustability at installation’ and such desks are referred to as ‘height selectable desking’.
In order to appreciate why we need height adjustability, first we have to understand how the height of a fixed height desk (720 mm for an office desk) is determined. This is not a magic number or Ergonomists’ favourite figure, it is determined by the ergonomics fact that someone who is working at a desk (sitting on a chair) should be able to get their legs under the desk without the tops of their thighs hitting the underside of the desk top whilst their elbows are just above the desk top. Hence, if we are to have one size fixed height desks, we have to design them for the tallest people in our possible user group (assumed to be the national 90th percentile male) so that they can get their legs under the desk.
This means that the majority of people who are shorter that the 90th percentile male (in other words 90% of males and a higher percentage of females) would find the desk either too high (if they adjust their chairs so that their feet can rest on the floor without the chair exerting pressure at the back of their knees) or their feet can’t touch the floor (if they adjust their chairs so that their elbows are just above the desk height).
People can’t work at desks, which are too high, as they would have to work with their shoulders and arms raised which would result in upper limb disorders (ie shoulder, neck and upper back problems). Consequently they would adjust their chairs so that their elbows are just above the desk height, but then their feet would not touch the floor and the chair would exert pressure at the back of their knees and hence constrict the blood supply to their legs and feet. Such postures if maintained for extended periods could result in the sensation of pins and needles and in very extreme conditions, deep vain syndrome.
To prevent this, such users would need to use a footrest. So, unless we custom build desks to suit individuals, the fixed height desks are wrong height for a significant proportion of the people, not just the short people but also the very tall people (those taller than the 90th percentile ie the top 10 %) who will not be able to get their legs under the desk. The most effective solution to the fixed height desk problem is clearly height adjustability. If one is concerned with adjustability one should always choose user adjustability. This is because adjustability at installation (height selectable desking) has a very limited advantage over fixed height desks.
If an employer knows that the majority of employees are short, the desks can be set at a lower height than the fixed height desks, or alternatively if the employees are very tall then desks can be set a higher height than fixed desk heights. The problem would still be there; the desk height would still be too high for the smaller people in that group who would still need a foot rest. The only possible advantage of height selectable desks are that these can be used to provide suitably high desks for very tall people in an organisation where they currently have fixed height desks.
The main advantages of truly user adjustable desking can be summarised as follows:
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