Tips for selecting and adjusting ergonomic chairs, and sitting properly

Today, in industrialized countries, many people spend the majority of their waking hours sitting; whether it's at home while watching television or on the computer, travelling to work in a car or bus, or working at a desk in front of a computer. Although sitting requires less physical effort than standing or walking, it puts stress on the lumbar area.

The effects of a sedentary lifestyle combined with a job that requires sitting can lead to many health problems.

Selecting the right chair and adjusting it properly is an important part in making your workstation safer. Also, learning and practicing how to sit properly can reduce stress and strain on your muscles, tendons, and skeletal system, and thereby reduce your risk of developing a musculoskeletal disorder.

Pick a seat
If you work in a sitting position, selecting a suitable chair is a critical step in preventing health problems. Choose a chair with:

• controls that are easy to operate from a sitting position,
• a seat that adjusts for both height and tilt,
• a seat that does not put pressure the back of thighs or knees,
• a seat with a front edge that curves towards the floor,
• breathable, non-slippery fabric on the seat,
• a backrest shaped to support the lower back,
• a stable five-point base,
• wheels or casters suitable for the type of flooring,
• a swivel mechanism,
• armrests that can be adjusted to the elbow height when your upper arms are hanging down and your forearms are at about a 90 degree angle to the upper arms, and
• armrests that do not interfere with free movements within the workstation. 

Adjust your chair to suit

Ergonomic chairs are designed to suit a range of people; however, a chair only becomes ergonomic when it specifically suits your body size, workstation, and the tasks that must be performed.

• Your chair should be fully adjustable. The optimal seat height is about one quarter of the body height - a general rule since the torso-to-leg ratio can vary widely.
• Stand in front of the chair. Adjust the height so thehighest point of the seat, (when in the horizontal position), is just below the knee cap.
• Sit on the chair and keep your feet flat on the floor.
• Check that the clearance between the front edge of the seat and the lower part of the legs (your calves) fits a clenched fist (about 5 cm or 2 inches).
• Adjust the back rest forwards and backwards as well as up and down so that it fits the hollow in your lower back.
• Sit upright with your arms hanging loosely by your sides. Bend your elbows at about a right angle (90 degrees) and adjust the armrest(s) height until they barely touch the undersides of the elbows.
• Remove the armrests from the chair if this level can't be achieved or if armrests, in their lowest adjustment, elevate your elbows even slightly.
• Tilt the seat itself forwards or backwards if you prefer.
• A well-designed chair allows you to sit in a balanced position. Buying an ergonomic chair is a good beginning but it may not bring the benefits expected. ●The actual sitting position depends on your personal habits; you have to learn and practice how to sit properly.

Take a good position

A neutral body position is a comfortable working posture in which your joints are naturally aligned. Working with the body in a neutral position reduces stress and strain on the muscles, tendons, and skeletal system and reduces your risk of developing a musculoskeletal disorder (MSD).

OSHA offers tips on how to maintain neutral body postures while working at the computer workstation:

●Hands, wrists, and forearms are straight, in-line and roughly parallel to the floor.

●Head is level or bent slightly forward, forward facing, and balanced - generally in-line with the torso.

●Shoulders are relaxed and upper arms hang naturally at the side of the body.

●Elbows stay in close to the body and are bent between 90 and 120 degrees.

●Feet are fully supported by the floor or a footrest may be used if the desk height is not adjustable.

●Back is fully supported with appropriate lumbar support when sitting vertical or leaning back slightly.

●Thighs and hips are supported by a well-padded seat and generally parallel to the floor.

●Knees are about the same height as the hips with the feet slightly forward.

●Working in the same posture or sitting still for prolonged periods is not healthy. Remember to change your working position frequently throughout the day by making small adjustments to your chair or backrest, stretching your fingers, hands, arms, and torso, and by standing up and walking around for a few minutes periodically.

Also, remember that the chair is only one of the components to be considered in workstation design. All the elements such as the chair, footrest (if needed), work surface, document holders, task lighting and so on need to have flexibility and adjustability to be "designed in."

More information

How to adjust office chairs fact sheet, CCOHS

Good working positions, OSHA

Office Ergonomics Safety Guide, CCOHS

Office Ergonomics e-course, CCOHS

It's a Stretch poster, CCOHS

Source: Canadian Centre for Occupational Health and Safety www.ccohs.ca