Ergonomics 4 Schools

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How many hours a day do you sit down?

Sitting is the most frequent body posture: we sit at work, at school, in the car, on the bus, on the train, at home in front of TV, to eat, to rest and so on. You are probably sitting down right now.

A seat should take the weight off your feet in order to lessen stress on your legs. It should provide some postural stability while you work or relax. You should be able to relax your muscles that aren't doing anything. The seat should also fit in with other furniture and equipment and not get in the way of what you are doing.

Types of seatTypes of seat
  • Seats for working e.g. office chairs, school chairs, kneeling chairs, perching stools.
  • Seats for leisure e.g. bar stools, dining chairs, easy chairs, cinema seats.
  • Seats for travel e.g. car seats, aircraft seats.
  • Specialised seats e.g. wheelchair seats, racing car seats.
What makes a seat comfy?

What makes a seat comfortable?

Generally, seats should allow your body to be comfortable and not restricted. The seat design is critical for this:

  • The seat height should not be so high so that your legs are left dangling! This would mean that there would be pressure on the soft tissues under your thighs. This pressure interferes with the return of blood from the lower limbs, which may cause tingling and numbness in the thighs due to pressure on blood vessels and nerves.

  • The seat depth should allow clearance at the back of your knees in order to prevent pressure on the network of blood vessels and nerves.

  • The seat back and angle should support the natural curves of your spine (in particular your lower back).

  • The main weight bearing should be taken by the ischial tuberosities (the bony parts of your bottom) and the top half of the thighs.

In addition, a chair should enable you to change posture at intervals, ensuring that different groups of muscles can be used for support, and that no particular group of muscles gets tired. The consequences of poor seating are discomfort, fatigue and inefficiency in what you are doing.

Legal requirements for seating facilities at work

The British Standard for Office Furniture (BS 5940) covers chairs, footrests, fixed and adjustable workstations.

Anthropometry for seat design

Anthropometry is the branch of human sciences concerned with body measurements such as body size, shape and strength. This is used by ergonomists to ensure that products, such as seats, fit and suit as many users as possible. See the anthropometry topic for more information.
If you are designing a seat, you need to take the following measurements into account.

Anthropometric estimates for British adults
aged 19-65 years (in mm, from Pheasant)

Dimension 5th %ile 50th %ile 95th %ile
A Sitting height 850 910 965
795 850 910
B Sitting shoulder height 540 595 645
505 555 610
C Shoulder breadth 420 465 510
355 385 435
D Hip breadth 310 360 405
310 370 435
E Buttock-popliteal length 440 495 550
435 480 530
F Popliteal height 395 440 490
355 400 445

('Popliteal' refers to the part of the leg behind the knee.)

Anthropometric measurementsAnthropometric measurements






Aches and pains can be suffered by office workers as a result of poor seating and workspace layout. But there is plenty that can be done to make them more comfortable.


  • The seat height should be adjustable. BS 5940 recommends a minimum acceptable range of 420-500mm. Pheasant (2001) suggests that a range of 380-535mm.

  • The seat edge should be rounded to minimise pressure under the thigh.

  • The seat pan should tilt forwards and backwards (about 5°).

  • The seat base should swivel and have 5 or more castors (for stability).

  • The backrest should be adjustable and about 500mm in height. It should also be contoured to support the lumbar curve of the back.

  • The backrest should tilt for support in both a working and resting posture.

  • If the seat and backrest do not adjust independently, the angle between them should be about 105°.

  • The upholstery material should not cause sliding or sweating.

  • Footrests should be provided to allow shorter people to adjust themselves to the desk or worktop (BS 5940 recommends a minimum 450mm length x 350mm width).

  • Armrests may prevent the user from getting close to the desk but they can assist resting the elbows during work. If they are fixed they should not extend more than about 200-250mm in front of the seat back.

Many office workers do not adjust their chair at work even though they know how to do so. To encourage them to do so and take advantage of all the adjustment mechanisms in their chairs, controls should be easy and intuitive to operate from the seated position.


An armchair supports the body during rest or relaxation, for example, when reading or watching television. The design of the armchair presents a dilemma. People usually sprawl in armchairs rather than sit up straight in them. Armchairs should allow the relaxation of muscles as well as support of the spine in its natural curve. Many armchairs fail to achieve this as they are often too deep and too soft with inadequate backrests (too low and poor shapes). This makes it very difficult to achieve 'good postures'. If the seat is too low, standing up and sitting down are difficult for some users. The seat height for comfort is not necessarily the same as the height required for ease of getting in and out of the chair. Appropriate armchair design is particularly important for older and disabled users.


  • The seat backrest angle should be 105-110°. A rake of more than 110° may cause problems for older users getting in and out.
  • Armrests should be slightly sloped so that they are lower at the back for comfort and higher at the front to enable easy rising from the chair.

Other considerations in armchair design are fire retardancy, type of upholstery, suspension, wear and tear, leg design (not yours!), headrests and the situation in which it is to be used.


Back pain is common amongst drivers and there are several reasons for this: driving forces prolonged sitting in a fixed posture; transference of vibration; and loss of spine support due to a poorly fitting seat.

Recommendations (in addition to those for general seating):

  • Good visibility of the road should be possible, together with a good view of all the instruments.

  • The driver should be able to reach all of the controls (pedals and hand controls) without stretching.

  • The body should be supported and muscular effort minimised to allowing the driver to concentrate on the driving task.

  • Shaping and padding should allow good distribution of body weight over the seat.

  • Vibration and shock transfer should be minimised.

In order to minimise discomfort, the driver's seat should also offer as many adjustable features as possible. The most important ones are:

  • Backwards and forwards adjustment of the seat,

  • Backrest angle adjustment,

  • Seat height adjustment – ideally independently adjustable at the front and rear of the seat,

  • Seat angle adjustment,

  • Adjustable lumbar (lower back) support - up/down and in/out,

  • Headrest adjustment - vertical, horizontal and tilt.

The more adjustable features within the car (e.g. steering wheel adjustment in/out, up/down and tilt), the greater the likelihood of the driver achieving good and comfortable postures. But any posture, no matter how good it is, can lead to discomfort if it is held for too long. Therefore, it is important to adopt a range of comfortable driving positions and to make frequent stops to avoid, or help delay, the onset of discomfort. Ease of use of any adjustable feature is therefore crucial.


Multi-purpose seats are intended for a variety of uses: in dining rooms, bedrooms, work areas, and as spare chairs. They are also used in public spaces such as waiting rooms, conference centres and libraries, where they often have to be stacked for storage. General requirements for seats can be applied to multipurpose chairs. However, such chairs will not usually be maximally comfortable in all situations and compromises will often have to be made. It is difficult to design a seat that is comfortable both for a forward-inclined posture (a dining table) and a backward leaning posture (listening to a talk). Taller and shorter users may be particularly uncomfortable with certain chairs.


  • The seat and backrest should be upholstered with a gently-rounded lumbar support.

  • The seat surface should be gently moulded with slight concavity under the buttocks.

  • The depth of the seat should not exceed 430mm in order that the backrest is effective for smaller users.

  • The height of a flat seat surface should be 400–460mm.

  • The material for the seat cover should allow for air circulation and not be slippery.

As compromises between postures, comfort and the purpose of the chair are unavoidable, a choice of models (e.g. different heights, profiles, upholstering etc.) is better for the consumer.


Seating FAQs

Q. I am designing a stool for my GCSE project and I need to research about ergonomics for a stool or seating. Can you help? Answer

Q. I'm designing a cockpit for an off road vehicle, and the seat is has to be very close to the floor of the vehicle, (right now the frame of the seat is bolted to the floor with a roughly 8 cm thick cushion/cover) should I have the seat angled and if so at what angle? Answer

Q. I am currently student teaching at an elementary school.  Is there any research indicating how long grade school students may sit at desks before they should get up to move around for their own health and safety?  I have heard that adults working in an office should stand up and move around every 15 minutes.  Are there standards for children? Answer

Q. I am making a chair that has no legs and is made from a metal base which mean that it will bend under the weight of the body. How do I make this chair ergonomically safe? Answer

Q. Why can't I just sit and work or type the way I want to?  What health problems could I develop if I do not follow ergonomic principles? Answer

Pheasant, S (1998) Bodyspace. Anthropometry, Ergonomics and the Design of Work. (2nd Ed.) London: Taylor & Francis ISBN 0748403264

Content: Diane Gyi
Images: IMSI's MasterClips Collection