Risk Factors For CTDs

Four physical risk factors (Other risk factors, not usually found in offices, include cold and vibration) act together at the keyboard:

  1. Repetition
  2. Excessive and/or Sustained Force
  3. Awkward Posture
  4. Lack of Adequate Rest/Recovery

The more a job exposes a computer user to the above conditions, the greater the chance of fatigue, or wear and tear on nerves, muscles and tendons.

One goal of ergonomic design is to reduce risk factors as much as possible.


No one should key constantly for eight hours a day. CTDs were not as common with typewriter use because a typist's hands rest more than a computer user's. A typist returns carriages, changes paper and ribbons and uses correction fluid or tape.

Excessive Force

Many computer users key with a much harder touch than necessary. Most keyboards need only light pressure to respond. A soft touch reduces the impact on your fingers.

Try this challenging exercise. (It's not as easy as it appears.) Practice keying with such a light pressure that no characters appear on the screen. Now increase the pressure just enough so that letters do appear. This is the amount of pressure you should use.

When you use more than the minimum pressure needed, you increase your risk of injury.

Awkward and/or Sustained Posture

Prolonged sitting stresses our bodies. Sitting contracts muscles which requires energy (just like dynamic activity does). But with dynamic work, our muscles contract and expand. This action removes waste and pumps new nutrients to the cells. Without movement, lactic acid builds up and causes fatigue.

When we move and shift our posture, our blood flow increases. Movement also distributes the weight to different parts of the body.

Rest and Recovery

Rest breaks and alternative work let the body recover from computer work. It's better to take several short breaks than one long one. In an alternative work break, a computer operator performs non-computer tasks.


Even with the best ergonomic furniture, VDT work involves constrained postures. To reduce this risk factor, many ergonomic guidelines suggest exercises.

You should use extreme caution when choosing exercises.

In a review of 127 recommended exercises, a study found that 90 percent of those exercises could cause problems for individuals with one or more acute or chronic musculoskeletel disorders (Lee et al. 1992). Forty percent of the exercises reproduced or exacerbated some of the physical or biomechanical demands of the job.

Exercises should not stretch already over-stretched muscles.

A good exercise program has the following components (Adapted from Lee, et al, 1992):

  1. Stretching of shortened and tensed muscles. This improves flexibility and circulation, and reduces muscle fatigue.
  2. Contracting or strengthening stretched and weakened muscles. This increases resistance to fatigue and discomfort, and promotes better posture.
  3. Movement of the spine. This relieves stress on lower back muscles and reduces the compression of intervertebral discs.
  4. Improvement of blood return from the legs.

Computer users have been known to continue exercises even though they cause pain. They assume that an exercise manual would not prescribe something harmful.


Consult a medical professional if you experience pain or have any questions about the effects of exercises.more.