Part E - Ergonomics

Health, Colour and Accessibility

Identify the Health Aspects of Ergonomic Design
How to avoid repetitive strain injuries

"Repetitive Strain Injury occurs when the movable parts of the limbs are injured. Repetitive Strain Injury [is] usually caused due to repetitive tasks, incorrect posture, stress and bad ergonomics" Safe Computing 2008

Health Issues | Colour | Accessibility | Exercises

In the chapter on productivity, we examined design in terms of layout and arrangement of controls, alignment of information and user interface standards.  In addition to these aspects of ergonomics, the following physical issues require attention

  • health issues
  • use of colour
  • accessibility

These issues affect the design of the equipment itself, the design of the interface and the design of the environment.

Physical ergonomics is important for everyone, and pressingly important for anyone who suffers mild or severe medical conditions such as arthritis, carpal tunnel syndrome, colour blindness, visual impairment, or auditory impairment.  Minor changes to equipment, interface, or environment might go unnoticed by those who do not exhibit medical symptoms, but might nevertheless cause enough pressure to lead eventually to chronic pain or to disability. 

Health care is one of the most dynamic and growing sectors of western societies.  While developed nations focus on cure and care, many developing nations focus on prevention.  Regardless of national status, relatively little is known about how people use computer equipment, how their environment affects their use, how their experience can be made more pleasureable and how supporting tools can improve accessibility. 

Health Issues

We don't normally think of computers as dangerous.  Yet, there are many situations in which health concerns do arise.

Physical Position

Consider users who work for long periods of time.  Placement of controls that requires them to assume uncomfortable positions will result in muscle strains, back problems, and headaches.

Standing is better than sitting, but where sitting is necessary, several variables need to be addressed to minimize health effects.

ibm keyboard
Workstation Variables (source: Berkeley Lab Wikipedia 2008 PD)

Health disorders that arise commonly from improper physical positioning include:

  • repetitive strain injury
  • carpal tunnel syndrome
  • muscular disorders

Repetitive strain injury is the general term used to describe prolonged pain due to soft tissue injury.  The injury can occur in the shoulders, hands, neck or arm.

Carpal tunnel syndrome is a pinching of the median nerve in the carpal tunnel.  The carpal tunnel is the passageway within the wrist that is surrounded by the wrist bones and that joins the distal forearm to the middle compartment of the palm.  The syndrome is an infammatory disorder of the tissues around the median nerve.  This syndrome can be caused by repetitive stress or by some physical injury. 

carpal tunnel
Carpal Tunnel (source: Pngbot Wikipedia 2007 PD)

Safe Computing Tips (


Temperature affects user performance.  User performance deteriorates when temperatures fall significantly outside the norm.  Temperatures within working environments should be controlled so that they remain comfortable for the user.

Temperatures ideal for productivity are between 21 and 23 degrees Celsius.  Lower temperatures result in muscle contractions that can increase the possibility of injury.  Higher temperatures decrease work efficiency. 

Canadian Centre for Occupational Health and Safety


Lighting affects user performance.  Users need adequate lighting to see computer screens without trouble.  The screen should be oriented so as to minimize reflections from windows or washing out by daylight.  Light sources behind monitors should be moved since the sources themselves create contrast making it harder to read the information on the screen clearly.

On the other hand, users need good lighting for reading and writing tasks on their desks.  This need imposes a lower limit on the lighting on monitors. 

The amount of light on a surface is measured in terms of foot candles or luxes.  The customary unit in the United States is the foot-candle.  One foot candle is the amount of light that impinges on the inside surface of a 1-foot radius sphere when the light source is one candela located at the center of the sphere.  A common candle emits light of intensity approximately equal to one candela.  The SI unit for illuminance is 1 lux.  One foot candle is 10.764 lux. 

Flourescent lights provide the worse type of lighting, incandescent lights are better and indirect natural light is the best.  Hoods and drapes reduce glare from the light sources.

Four 40-watt flourescent bulbs on a 9-foot ceiling create about 50 foot canldes of lighting.  Removing one of the bulbs can reduce the lighting intensity significantly.


Bright displays on monitors can strain the eyes and lead to eye fatigue.  Any direct brightness on or from a computer screen should be limited. 

The lighting for reading from paper or a CRT display should range between 20 and 50 foot candles.  The lighting from LCD monitors should be higher and may have to be up to 73 foot candles. 


Noise affects user performance.  Noise is the common term for unwanted signals.  Noise can distort, change or block information transmitted in an interaction.  Although noise often refers to unwanted sounds, it can also refer to unwanted video signals (snow), unwanted thermal effects (generated by equipment), and unwanted visual effects (grain). 

Excessive noise is a health hazard.  Computer equipment should produce a low level of noise that is not disturbing.  Sound should be used judiciously in the user interface since sound can at times be more distracting than helpful.

Noise is measured in decibels.  A decibel is a logarithmic measure of intensity with respect to some reference level.  The reference level is usually the threshold of perception.  The reason for using the logarithmic scale is that the human ear is capable of detecting an extremely large range of sound pressures.  The logarithmic scale makes that range tractable.

 Source   decibel level  
 Auditory Threshold  0 dB 
 Calm Breathing  10 dB 
 Normal Conversation  40-60 dB 
 TV Set - home level  ~ 60 dB 
 Possible Hearing Damage due to long-term exposure    78 dB 
 Possible Hearing Damage  120 dB 
 Pain Threshold  130 dB 
 Jet Engine at 30 m  150 dB 

Sound Intensity Levels - sound in air (source: Wikipedia 2009)


Time spent using a computer can affect user performance and should be controlled.  Too much time spent can result in

  • repetitive strain injury
  • fatigue
  • overexposure to harmful emissions from CRTs


One of the most important items of physical equipment is the chair.  Select the chair that is the most comfortable.  Its height and tilt should be adjustable.  Adjust its height and tilt to maximize comfort.

The best angle for the chair back is about 120 degree from the seat.  The chair back should provide about 5-6 cm of support for the lumbar region of the human back.  This support is crucial to avoiding excess pressure on the disks of the lower spine. 

lumbar support
Lumbar Region (source: Mariana Ruiz Villarreal Wikipedia 2004 PD)

A proper kneeling chair can also achieve the desired tilt and lumbar support by inclining the knees towards the floor.

kneeling chair
Kneeling Chair (source: Usher Wikipedia 2004 CC-BY-SA)


The keyboard can affect user performance.  Its placement and tilt are important ergonomic variables.  Adjust the height to minimize the bending of the wrist.  Arms should hang loose to avoid the cramping of shoulders.  Forearms should have some support.  Quite often, the chair itself provides this support.

Some Commercial Products

Microsoft has been producing its own line of ergonomic keyboards since 1994.  It refers to its designs as natural since they accomodate the hand positioning for typing that is natural. 

microsoft natural keyboard

Microsoft Natural Ergonomic Keyboard Pro 1999 (source: PCStuff Wikipedia 2006 CC-BY-SA)

Maltron has been specializing in the production of ergonomic keyboards since 1977.  It produces keyboards designed to reduce and to eliminate repetitive strain injury as well as addressing special needs. 

DataHand is another company that produces ergonomic keyboards.  Their design minimizes the absolute amount of finger movement. 

datahand keyboard

Microsoft Natural Ergonomic Keyboard Pro 1999 (source: PCStuff Wikipedia 2006 CC-BY-SA)

Video on DataHand Keyboards (


The type of mouse can affect user performance.  The standard computer mouse is not designed for prolonged use.  Specialized mice have been developed for prolonged use.  These are designed to relieve hand tension and to avoid repetitive strain injury. 

If you do have a standard mouse, hold it lightly and avoid white knuckles.  Use your whole arm and shoulder to move it, not just your wrist.  Avoid maintaining the same position for prolonged periods of time.

Some Commercial Products

3M came out with an ergonomic mouse in 2004.  It keeps the palm perpendicular to the work surface simulating a handshake.  This design supposedly relieves pressure on the median nerve of the wrist. 

In 2007, Microsoft produced its own ergonomic mouse that sits between the 3M ergonomic mouse and the standard mouse.  This mouse leaves the palm parallel to the working surface but does result in reduced stress. 

microsoft natural mouse

Microsoft Natural Wireless Laser Mouse 7000 (source: Biozinc Wikipedia 2008 CC-BY-SA)

Ergonomic Mouse Reviews (

Safe Computing Tips (

Other Human Issues

In addition to health issues arising from the use of equipment or from the environment, ergonomic topics include posture, eye relief, and sound relaxation. 

Assume a posture that is comfortable but not rigidly straight.  Loosen your muscles, stretch and roll your neck even before you start to work.  Take breaks at least once an hour - get up and move around.

Take breaks from viewing a screen.  Go for a walk particularily where you can keep looking into the distance.  Parks and open areas are ideal in this respect. 

Take breaks from listening to the audio produced by your computer.  Go for a walk in some natural environment devoid of computer generated sounds.  Once again, parks are ideal in this respect. 

Use of Colour

Use colour sparingly and judiciously.  Overuse can make an interface distracting or confusing.  Poor selection of colours can make some users unhappy.  Interfaces that look like circuses are not good interfaces. 

Select Colours

Colours should have sufficient contrast to be clearly discernable.  Do not use blue to display of any critical information.  If a colour serves as a cue, then use some other cue as well so that colour-blind user can use the interface.

Colour selection should conform to user expectations from everyday conventions:

  • red - stop
  • green - go
  • yellow - hold or caution

Keep in mind that the meaning of different colours differs across cultures and might need to be localized. 

Colour Scheme Designer (


To test the usability of a colour in an interface, turn the saturation down to the point where the display is purely monochrome.  Is the interface still usable?


Accessibility is the ergonomic measure of how many people have access to a certain product.  The goal of universal accessibility is to make a product accessible to all users who wish to use the product.  Accessibility is not tied to users with some form of disability.  For instance, a train station is accessible to a mother with a child in a stroller if the mother and child can pass through the station using their stroller. 

The numeronym for accessibility is a11y, where the 11 stands for the number of letters omitted. 

In HCI, accessibility can be a software problem, a hardware problem or a combination of both. 

Assistive Technologies

Assistive technology refers to the group of devices or methods designed to help people with disabilities improve their own access to products that are readily available to people without disabilities.  Disabilities include

  • cognitive impairment and learning disabilities - such as dyslexia, ADHD or autism
  • vision impairment - such as low vision, glaucoma, partial or complete blindness or colour blindness
  • hearing impairment - such as deafness or hard of hearing
  • motor or dexterity impairment - such as paralysis, cerebral palsy, carpal tunnel syndrome, or repetitive strain injury, each of which affects typing or use of the mouse


Microsoft Windows provides numerous assistive tools:

  • a narrator that reads text off the screen, announces the active window when it changes and can read text as it is being typed
  • a flashing caption bar or active window when the interface makes a sound
  • a sticky key facility to enable series input of a compound key stroke
  • high-contrast text to enhance visibility
  • an on-screen keyboard allows typing using a mouse
  • a magnifying glass to show a portion of the screen enlarged
  • the ability to change font sizes makes text easier to read

You can find more information on the features in Windows at Accessibility in Windows Vista and in Windows 7.

Accessibility Guidelines

The World Wide Web Consortium published its WCAG in 1999 under the Web Accessibility Initiative (WAI).  In December 2008, WAI published version 2.0 of its WCAG. 

Some notable parts of WCAG 2.0 are:

  • provide text alternatives - alt tags for images, transcripts for audio and video files
  • make the site fully keyboard accessible - mouse technology is not necessary
  • session timers should be extensible or disableable
  • adaptable - viewable in different formats without loss of structure or meaning
  • distinguishable - provide colour contrast to enhance readability
  • readable - avoid jargon - content should be easy to understand
  • navigable - include a site map, navigation should have a logical structure
  • predictable - consistent structure, keep main regions in the same location on each page
  • input assistance - include error messages for forms, avoid the colour red for errors
  • compatibility - with popular browsers and assistive devices

The Canadian government has common look and feel standards for all of its websites.  These Web Content Accessibility Guidelines (WCAG) ensure that the sites can be used with assistive technologies in a uniform manner and were updated in 2007.  They implement WCAG 1.0. 

The Ontario Legislature has recently received the final submission of the Accessible Information and Communication Standard.  Once this standard comes into effect, the legislation will require web site compliance with WCAG 2.0.  The implementation period will extend over 3 years. 

An interesting article on WCAG 2.0 implementation throughout the world by Roger Hudson