Ergonomic design helps prevent injury by adjusting the job to the worker and reducing physical stress. Workstations can be designed so each worker may work in natural and comfortable body postures which prevents stress, strain, and discomfort. However, the best designed station will not prevent injury if the proper work practices and techniques are not in place to prevent repetitive movements, reduce muscle strain, and improve productivity. This handout provides a checklist for evaluating your computer workstation and recommendations for modifying the arrangement to provide optimal comfort.
NEUTRAL BODY POSTURE
To understand the best way to set up a computer workstation, it is helpful to understand the concept of neutral body positioning. This 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. The following are important considerations when attempting to maintain neutral body postures while working at a computer workstation:
4 Hands, wrists, and forearms are straight, in-line and roughly parallel to the floor.
4 Head is level, or bent slightly forward, forward facing, and balanced. Generally, it is in-line with the torso.
4 Shoulders are relaxed and upper arms hang normally at the side of the body.
4 Elbows stay in close to the body and are bent between 90 and 120 degrees(°).
4 Feet are fully supported by floor or footrest.
4 Back is fully supported with appropriate lumbar support when sitting vertical or leaning back slightly
4 Thighs and hips are supported by a well-padded seat and generally parallel to the floor.
4 Knees are about the same height as the hips with the feet slightly forward.
These four reference postures are examples of body posture changes that all provide neutral positioning for the body.
|Upright Sitting Posture
|The user's torso and neck are approximately vertical and in-line, the thighs are approximately horizontal, and the lower legs are vertical.
||The user's legs, torso, neck, and head are approximately in-line and vertical. The user may also elevate one foot on a rest while in this posture.
|Declined Sitting Posture
||Reclined Sitting Posture
The user's thighs are inclined with the buttocks higher than the knee and the angle between the thighs and the torso is greater than 90°.
The torso is vertical or slightly reclined and the legs are vertical. The user's torso and neck are straight and recline between 105 and 120° from the thighs.
Posture Evaluation Tools
Are your shoulders relaxed? (reduces stress)
Are your elbows bent at 90-120°? (helps keep wrists straight)
Are your wrists straight? (keeps pressure off muscles, tendons and nerves in wrist and hand)
Are your ears, shoulders, and hips lined up vertically? (maintains proper sitting posture)
Are you positioned square in front of the monitor and keyboard, not be twisted or contorted in any manner?
Sitting places more stress on the lower back than standing or lifting. Proper sitting posture is essential in reducing stress on the lower back. To be seated properly in your chair your feet must rest flat on the floor or on a foot rest (you should use a foot rest if your chair does not adjust low enough or if your work surface is too high.) The key is to not only have your feet flat on the floor (or supported by a foot rest), but also to have your thighs parallel with the seat pan so your legs form approximately a 90° angle at the knees.
If your chair has a vertically adjustable back with an outward contour in the lower back section (the lumbar support), adjust the back of your chair so the lumbar support fits in the small of your back. If the chair does not have a lumbar support, place a rolled up towel or small pillow in the curve of your lower back for support. If the chair back is adjustable forward and backward, adjust the angle to what is comfortable for you, and where your trunk and upper legs form an angle somewhere between 90-120°.
If your chair has arms, they should not interfere with you getting close to your work. In addition, when you assume the typing position with your arms resting comfortably at your side, the chair arms should be at a height where they just barely contact your elbows. The chair arms should not noticeably elevate your shoulders or force you to move your arms out to use them.
Chair Evaluation Tools
Is your chair height adjustable so that your thighs are horizontal, feet rest flat on the floor or on a foot rest, knees are bent forming approximately a 90-120° angle, and arms and hands are comfortably positioned at the keyboard?
Is your chair back contoured to support the lower back and fit the curvature of your spine, or do you have a pillow or lumbar support added?
Is there room (1" - 4") between the front edge of the seat pan and the back of your knees?
Does your chair allow you to get close to your work?
Do your chair arms allow you to sit with your shoulders relaxed and not elevated?
Is the chair mounted on no fewer than 5 casters?
Does the seat pan have a "waterfall" front edge design? (provides an even distribution of body weight)
Does your backrest lock in place into a position that provides a firm back support?
WORK SURFACE/KEYBOARD/POINTING DEVICE
If your work surface is adjustable, first adjust your chair as mentioned above. Rest your arms comfortably at your side and raise your forearms to form a 90-120° angle with your upper arms. Adjust your work surface so the home row of your keyboard (the row which has the letters a,s,d...) is at approximately elbow level. If your work surface is too high and not adjustable, adjust your chair to bring your elbows to the home row level of the keyboard. If you raise your chair, then make sure your feet are properly supported.
In order to maintain wrists and neck in the straight neutral positions, sit square in front of the monitor and keyboard. The wrists should be kept straight. Bent wrists cause pressure on the hands and the carpal tunnels of the wrists, and long term repetition of this can lead to cumulative trauma disorders. A wrist rest pad helps to reduce the amount of stress on the wrists and hands when not typing. Select a thick, soft wrist pad to minimize soft tissue compression. Always keep wrists straight while typing and ONLY use the wrist rest when you are not typing. A wrist rest can also prevent wrists from coming in contact with the sharp edge of the desk or keyboard tray.
If you use a pointing device (mouse, trackball, touch pad, etc.), make sure it is at the same level and approximately the same distance as your keyboard. Reaching for your pointing device or having it at a higher level than your keyboard can cause stress. Keyboard drawers or other types of keyboard support devices can increase the amount of desk space but can force you further away from your primary work surface, and if not large enough to hold the mouse as well, puts your mouse at a higher level.
Work Surface Evaluation Tools
With your chair adjusted properly, is your work surface at approximately elbow level?
Are your shoulders relaxed and not elevated when you work at your work surface?
Is there approximately a 90° angle between your forearms and upper arms and are your elbows close to your body?
Are your wrists in line with your forearms, not bent upwards, downward, or side-to-side, and kept straight when typing?
Do you have a wrist rest to prevent contact with sharp or square edges on your work surfaces and ONLY use it between typing?
Are you square in front of your keyboard, and is your keyboard centered so that the center of the alphabet (not the center of the keyboard) is in line with the center of your body (unless you are performing extensive 10-key)?
Is your keyboard flat (i.e., are the legs on the back of the keyboard NOT extended)?
Is your pointing device (mouse, trackball, touch pad) at the same level as your keyboard?
Once you have your chair and work surface height adjusted, adjust your computer monitor so the top of the screen is at or just below eye level with minimal glare. Placing the top of the monitor at eye level reduces unnecessary neck strain. Wearers of bifocals and trifocals often unknowingly tilt their heads backwards so they can read the screen through the lower portion of their glasses. This can sometimes lead to neck, shoulder, and back discomfort. Potential solutions include either lowering your monitor or purchasing glasses designed specifically for working at the computer.
Monitor Evaluation Tools
Is the viewing distance to your computer monitor somewhere between 20"-40" (approximately an arm's length)?
Is the top of your computer screen at or just below eye level?
Do you adjust the contrast or brightness of the screen to a comfortable level as the light in the room changes? (This may have to be done more than once a day.)
Is your computer monitor positioned to minimize glare or reflections from overhead lights, windows, and other light sources? Suggestions to minimize glare includes:
- Screens should be positioned so that windows are not directly in front of or behind employees when seated.
- Draw the drapes or adjust blinds.
- Adjust desk lamp or task light to avoid reflections on the screen. Light sources should come at a 90° angle, with low watt lights rather than a single high watt bulb.
- Reduce overhead lighting (where possible) by turning off lights or switching to lower wattage bulbs.
- Use indirect or shielded lighting where possible.
Keep the monitor screen clean by frequent dusting.
Where it is impossible to avoid reflections or adjust lighting, an anti-glare filter placed over the screen can be helpful. However, filters may affect the clarity of the image on the screen and should be tried only after other methods of reducing glare have been exhausted. An electrically grounded nylon micromesh glare filter is effective also in removing static charge from a screen.
WORK STATION ACCESSORIES
Keep your most frequently accessed items close to you to minimize the amount of reaching you have to do. Place all necessary items in an area you can safely reach without your upper back leaving the seat's backrest or twisting your back. If you type and reference material from paper, consider using a document holder placed at the same distance and height as the computer monitor to prevent repetitive movement of the eyes or neck from the paper to the screen.
Talking on the phone with your neck bent to hold the receiver can cause neck, shoulder, and back discomfort. If you are on the phone a fair amount of time,a phone headset can prevent you from bending your neck and prevent or relieve neck, shoulder, and back discomfort.
Accessory Evaluation Tools
Do you have enough room on your work surface for all your computer accessories?
Are your most frequently accessed items (e.g. phone, manuals, etc.) easy to reach?
Do you have an adjustable document holder to hold paper for prolonged computer inputting?
If a large percentage of your time involves using a phone, do you use a phone headset?
It is important to take breaks when constantly performing the same motions. Repetitious static work (such as working at a computer) is very fatiguing on the upper extremities, back, and eyes. Your body needs periodic breaks to allow different muscles to be used and to allow for better circulation. Taking a break does not mean stop working. It means doing something else.
It is also very important to change positions periodically. Sitting in one position or leaning on your arms for an extended period of time can interfere with circulation. Moving around can help with circulation and prevent you from putting pressure on one location for an extended period of time.
Work Habit Evaluation Tools
Do you take short breaks from repetitive motions every 20 - 30 minutes?
Do you frequently change body positions while working?
Do you provide your eyes with vision breaks periodically?
Employees whose job requires them to lift items on a regular basis should be provided with specialized training to prevent injuries from occurring. Office personnel who may have the occasion to lift heavy objects are more likely to hurt themselves because they do not perform lifting on a regular basis and generally do not follow safe lifting practices. Lifting procedures are as follows:
- Size up the load to make sure it can be handled safely. If the load is too bulky or too heavy, ask someone to help or try to break it up into smaller, more manageable loads. If the load is above and must be brought down, test its weight by pushing up on it.
- Choose the flattest, straightest, and clearest route, even if it is a little longer.
- Face and stand as close as possible to the load with feet wide apart.
- Squat down bending at the hips and knees keeping the back as straight as possible.
- While gripping the load, arch the lower back inward by pulling the shoulders back and sticking the chest out, make the lift smoothly and under control.
- Keep your ears, shoulders, and hips aligned.
- Position the load close to your body so the weight will be centered.
- Keep your elbows resting against your sides.
- Keep the weight of the load evenly balanced.
- When placing the load down, squat down, bending at the hips and knees, keeping the lower back arched in.