Computer Ergonomics - Avoiding MSD and RSI

Preventing MSD/RSI


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Introduction
What Is MSD & RSI?
Preventing MSD/RSI
Preventing Eye Strain
Healthful Work Habits
Safety & Comfort Checklist (Summary)
Copyright © 2012-2013 by Matthew S Harris

Matthew S Harris is a software & database designer, contract programmer & consultant.

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The basic techniques for avoiding MSD and RSI are to use good ergonomics in your workstation, and to engage in healthful work habits and lifestyle.

Ergonomics is the study of adapting work or working conditions to suit the worker. This section describes basic ergonomic posture, briefly describes correct ergonomics for working at a desk without a computer, and then describes the correct ergonomics for a computer workstation in detail.

Basic Ergonomic Work Postures

The basic elements of good ergonomic posture involve three points:

Working At Your Desk

When working at your desk (using pencil and paper, as opposed to using your computer), you should sit upright, with your weight slightly forward. Keep your work close to you, and your forearms flat on the table-top. Your hips should be slightly higher than your knees, without putting pressure against the backs of your thighs from the edge of your chair's seat. If your chair has a tilt-adjustable seat, it should be tilted slightly forward.

Computer Workstations

When working at your computer, you should sit upright in a relaxed posture, with your weight slightly to the rear. Avoid either slouching forward, or leaning too far back. Your knees should be slightly higher than your hips, especially avoiding pressure on the backs of your thighs from the edge of your chair's seat. If your chair has a tilt-adjustable seat, it should be tilted slightly back.

Ergonomics At Your Computer

Correct Computer Work Posture

Figure 1 – Correct Posture for Computer Work

This section explains correct posture while working at your computer, and describes how to correctly determine the height for your chair, desk or table top, and monitor display. This section also describes how to correctly position your mouse and keyboard.

Computer Work Posture

Keep your shoulders relaxed, with your forearms and wrists parallel to the floor. Adjust your table and chair heights so that your forearms are parallel to the floor, with your wrists straight (refer to Figure 1). You should be able to maintain the correct arm position and place both feet flat on the floor. If you cannot place both feet flat on the floor without pressure on the backs of your thighs, use a footrest to raise your knees. Sit against the back of your chair, and position your chair's backrest so that your lower back is firmly supported.

Most computer workstation furniture has height-adjustable table tops and monitor shelves. Preferably, you should adjust your chair for correct leg height, then adjust the height of your table top for the correct arm position. If your table is not height-adjustable, adjust your chair height to obtain the correct arm position, and then use a footrest to obtain the correct leg position.

Monitor Height & Position

Position your display monitor directly in front of you at a comfortable viewing distance; typically about 18 to 24 inches. If you use a document holder, position it at the same level and near the display monitor.

Keeping your neck straight is an important part of computer ergonomics. The height of your monitor tends to control your neck position. If your monitor is too high, you'll end up tilting your head backwards, resulting in neck strain.

There are two basic rules you can apply to determine the correct monitor height for you:

 

Positioning & Using The Keyboard

Proper Keyboard Wrist Position

Figure 2 – Proper Keyboard Wrist Position

Your keyboard should be directly in front of you so that you can reach it easily with your elbows remaining in a relaxed position at your side. Remember to keep your shoulders, arms, wrists, and hands relaxed as you type, with your upper arms hanging freely at your sides. When typing, keep your wrists straight (refer to Figure 2). Do not splay or arch your wrists up or down (Figure 3), or to the sides (Figure 4).

Avoid resting your arms or elbows on the edge of the table. Use a wrist pad to support your wrists and/or cushion the edge of a table, but don't let the weight of your arms rest on the pad.

If you have a chair with arms, don't rest your elbows or forearms on the arms of the chair while working. Doing so has two negative effects: first, resting your elbows or forearms on the arms of the chair tends to lock your arms in place. With your arms immobilized, you are more likely to splay or arch your wrists and/or experience shoulder pain. Secondly, resting your elbows or forearms on the arms of the chair is another source of point-pressure which may affect circulation and/or put direct pressure on nerve bundles.

It is best to use a chair without arms for computer typing and mouse work.

Don't Do This: Wrists Flexed Up Or Down

Figure 3 – Don't Do This: Wrists Flexed Up Or Down

Don't Do This: Wrists Flexed In Or Out

Figure 4 – Don't Do This: Wrists Flexed In Or Out

 

 

 

 

 

 

 

Positioning & Using The Mouse

Position the mouse at the same level as the keyboard, and within easy reach. Like the keyboard, you should use the mouse with your forearm parallel to the floor, and your wrist straight (refer to Figure 5). Make sure that the thickness of the mouse pad does not raise the mouse higher than your elbow, forcing you to bend your wrist.

Proper Mouse Wrist Position

Figure 5 – Proper Mouse Wrist Position

Use your whole arm to move the mouse. Hold the mouse with a relaxed hand; avoid gripping the mouse tightly.

Many people experience strain when using a mouse in activities that involve a lot of dragging or double-clicks. Keep in mind that MS Windows can be configured so that items usually selected with a mouse click are selected when the mouse pointer is moved over the item, and that items activated with a double-click can then be activated with a single click. Also, a multi-button programmable mouse can help eliminate strain in the hands. Typically, you configure one or more of the mouse buttons to provide a double-click, without the user actually having to double-click.

If you perform many mouse-drag operations, you may find it easier and more comfortable to use an alternate pointing device, such as a trackball. A trackball avoids stress on the finger tendons by using the fingers to perform delicate maneuvers and the thumb for clicks. Because the thumb tends to be much stronger than the fingers, a trackball may alleviate fatigue associated with using a mouse.

The same basic recommendations for using a mouse apply when using trackball or touchpad pointing devices — keep your wrists straight and relaxed, parallel to the floor.

 

Arm & Hand Motion

Use natural, comfortable motions to avoid strain. Keep your mouse and keyboard within easy reach. Also keep frequently used work materials within easy reach; frequent over-extension to reach reference books or other work materials may result in injury.

Use these motion guidelines when working at the computer:

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