To be seated properly in your chair your feet must rest flat on the floor. You should use a footrest 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 degree (or greater) angle at the knees.
If your chair has an adjustable back up and down with an outward contouring in the lower back of the chair (the lumbar support), adjust the back of your chair so the lumbar support fits in the small of your back. If the chair back is adjustable forward and backward, adjust the angle to what is comfortable for you. The angle you prefer is rather subjective; you should adjust the back angle of your chair so your trunk and upper legs form an angle somewhere between 94 -115 degrees.
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 wing your arms out to use them.
For the proper work surface/keyboard height do the following: if your work surface is adjustable, first adjust your chair as mentioned in the chair adjustment section above, then with your arms resting comfortably at your side, raise your forearms to form a 90 degree 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 make sure your feet are properly supported.
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.
Bifocal and trifocal wearers have to pay particular attention to the placement of their monitor. 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 computer monitor or purchasing glasses designed specifically for working at the computer. If glare is a problem either reorient your monitor or purchase a glare screen.
If you use a mouse, make sure it is at the same level and at approximately the same distance as your keyboard. Try to keep your pointing device as close to the centerline of your body as possible. Reaching for your input device or having it at a higher level than your keyboard can cause problems. Keep your most frequently accessed items close to you to minimize the amount of reaching you have to do. If you type and reference material from paper you should consider using a document holder or slant board. Place the document holder at the same distance and height as your computer monitor. The document holder will help in keeping your head over your spine and can prevent or relieve neck, shoulder, and back discomfort.
Talking on the phone with your neck bent to hold the receiver can cause neck, shoulder, discomfort. If you're 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.
It's very important to take a break from working at your computer every hour. Repetitious static work (working at a computer) can be very fatiguing on your upper extremities as well as your eyes. Your body needs periodic breaks to rest and recover. Taking a break does not mean you have to stop working, you could make a trip to the copier, talk to a colleague, make some phone calls, etc.
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.
It is often working overtime and the stress of deadline situations that force people to ignore and work through their pain and discomfort. It is very important that once you start to notice some pain or discomfort to be very careful. Pain that goes away over night is usually a sign of fatigue, pain that is continuous and does not go away over night is more serious and should be attended to immediately. Ignoring pain can lead to serious injury.
Finally be careful with what you do outside of work. Repetitive stressful activities outside of work (e.g. home improvement projects, hobbies that require repetitive motion, etc.) can sometimes lead to repetitive motion injuries as well. When working on a new task you should treat it just like preparing for a race. Whenever you engage in a new task gradually build up your strength and endurance, don't just jump right in.