Typically, there are 3 seated positions, depending on the type of work done; reclined, upright, and forward. The goal is to adjust the chair and workstation to the most frequently used seated activity. For example, driving is an upright activity; reading and writing are forward-oriented activities. People with poor compression tolerance may find the reclined position more comfortable. Despite the position, the goal is to keep the spine supported in a neutral position and avoid repetitive and excessive spine and extremity motions that lead to pain. Ergonomic principles can be used to adjust the various components of your workstation so that you may maximize the use of proper posture and body mechanics.
Standing workstations may be used for people who cannot tolerate sitting well, usually because of low back problems. Combination sitting/standing workstations may be used for people who cannot tolerate a full day of sitting or standing and need to change their work positions frequently.
If you have a seated workstation, start with the chair, as this is the base of support and will affect all other adjustments.
Seat height is very important:
- Weight should be evenly distributed along the length of the thighs.
- If you need to move about your workstation or reach frequently, it is much more effective to have your feet on the floor when in the upright or forward position.
- Support the feet with a footrest if your feet do not rest flat on the floor.
- As the seat lowers, the hips will lower and the knees will relatively rise. If your knees are higher than hip level, it will become easier to "slouch"; slouching can be offset by making sure the seat back is near vertical and can be locked into a position that supports the neutral lumbar position.
Seat depth and tilt
- Edge of chair should extend to 1 to 3 inches from the back of the knees.
- Contoured front edge is helpful to avoid pressure on the thighs.
- Seat and back angle between 90 and 130 degrees. Again, this depends upon the task.
- Use a slightly forward tilt of the seat pan for forward tasks, a level seat pan for upright tasks, and slight backward tilt for reclined tasks.
- With any position, make sure the back position is in neutral. When reclining, be cautious that the head and neck do not move forward, to avoid straining the neck muscles. It can be helpful to have a high back chair to support the head and neck.
- Contour should match or be modified to match the contour of the spine.
- A high back rest that supports the head can be very helpful for those with neck problems or weak neck muscles who sit upright.
- Arm rests are optional. They may be helpful for shoulder/neck support.
- If the elbows lean on the rests while typing or doing upper extremity tasks, circulation in the elbow or forearm may be cut off.
- Elbows should not be planted on arm rests while typing because excessive motion will be forced at the wrist and hand.
- Tilt: Keep the keyboard flat with the hand in a relaxed, cupped position which places the wrist in neutral. If the keyboard is tilted, the wrist will go into backward bending (extension). A negative keyboard tilt (downward) may also be used to avoid wrist extension.
- Distance: The closer the keyboard is to the body, the more the wrists bend laterally (towards the little finger). If the keyboard is too far away from the body and the upper arm moves more than 25 to 30 degrees forward of the body, the shoulders and neck will fatigue.
- Height: The elbow angle should be maintained at 90 degrees or greater (arms horizontal or lower) where the wrist and hand are most comfortable. If the hands reach above the elbows, the shoulders tend to elevate.
- The mouse should sit next to the keyboard at the same distance and height.
Monitors and source documents:
- The top of the screen should sit slightly below eye level.
- The distance of your eyes from the screen should always be within the most comfortable viewing range.
- Use a document holder (attached to the monitor or freestanding) to support source documents at the same height and distance as the monitor to prevent eye and neck strain.
- A slant board may be used for reading and writing to keep from bending down too much.
Keep items used most frequently in the near reach zone, that area from elbow to finger tip.