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Ergovera's Ergo Savvy Newsletter )
 We help protect people, your company's most valuable asset April 2003 

In This Issue
That Pesky Mouse - Part 2
Research: Age, Gender and Alternative Pointing Devices
New: Special Daily Rates
Credits and notices

Published by Ergovera Ergonomic Consulting to help you keep up on ergonomic innovations, so you can protect your employees and increase their productivity. Please pass it on to your colleagues and friends.

The computer mouse struggle continues. My attempt to use a gel-topped articulating armrest for forearm support was unsuccessful. It was too tall and raised my shoulder into an uncomfortable position. In addition, I don't like a static arm position when mousing. I have a regular (i.e., non-articulating) shorter armrest on order, but am wondering if I will like it any better.

Meanwhile, I have evaluated a few hand/wrist supports with the help of several clients of mine. After trying a few different products we agree that simple 3X5" gel pads (that are 1/2" tall) work best. They are good from a cost perspective as well, since they are under $18.00 as compared to $30.00 - $45.00 products.

I continued to research the mouse this month. I chose research that looked at the difference between young and old computer mouse users and two studies that looked at alternative input devices, including the trackball. The research is not conclusive regarding whether certain computer mouse tasks are more difficult than other tasks (e.g., mouse clicking vs. movement of the mouse). However, in one study double clicking was found to cause the highest muscle activity.

An optimum pointing device appears to be difficult to design because even if a product positions the arm in the recommended neutral arm ("handshake") position or decreases the muscle activity in the shoulder (such as the trackball has been shown to do), computer users don't always like them. The reason they don't like them is not always clear. It may be primarily because they are not used to alternative devices as compared to the traditional mouse. The other primary difficulty seems to be that even if a device is good for one part of the body, say the shoulder, it is not necessarily good for another part (e.g., the wrist). Such may be the case with the trackball, especially if it is used without a wrist pad.

Two of the studies described workstations that included height adjustable tables, while one did not specify what type of workstation was used. The two studies with height adjustable workstations recommended the use of the work surface for forearm support. They found relatively low muscle activity in almost all muscle groups with this type of workstation design. Another study found a substantial lower muscular activity when the work surface was slightly lower than the subject's elbow height (as compared to when the work surface was slightly higher). The researchers also found:

  • Gender differences that indicate greater muscle activity in the right trapezius and deltoid muscles in women.
  • Women rotated their right shoulder outward more than men when using either a mouse or a trackball.
  • Higher shoulder muscle activity during computer mouse use was found in the older computer users as opposed to the younger computer users.
  • Subjects had a greater preference for the standard mouse over the trackball or "Neutral Mouse", which is a prototype mouse that is not on the market [Note: It is similar to the 3M Renaissance mouse in shape.]

So, when evaluating the work surface that the keyboard and mouse rests on, be sure it is slightly lower than the employee's elbow. Be careful when selecting alternative pointing devices and use gel pads as necessary to help keep wrists level with the arm (especially with trackballs).

Have a safe day,

Deidre Rogers, RN, MS, CAE

A Danish study (Lausen & Jensen) studied shoulder muscle activity in young and older computer mouse users. They found that shoulder muscle activity appears to increase with age, but only increases a minor amount by the type of computer mouse task performed. Double clicking the mouse was shown to elicit the greatest muscle activity. They found low deltoid and trapezius muscle activity when the work surface is used for forearm support. Height adjustable workstations were used in this study.

A Swedish study (Gustafsson & Hagberg), found that muscular activity in the muscles of the forearm decreased with the use of a "Neutral Mouse" ("handshake" posture). Subjects found the neutral hand posture "more restful and convenient for the hand and wrist" but all preferred the traditional mouse. The researchers thought that this preference was most likely due to the fact that computer users are more familiar with the traditional mouse. The majority of the subjects rated the neutral mouse as less comfortable overall than the traditional mouse. This may be because the neutral mouse requires greater arm movement and increases the use of muscles of the arm. A 24% decrease in productivity was shown with the neutral mouse.

Another Swedish study (Karlqvist et. al.) evaluated the difference between computer mouse use and use of the trackball as well as gender differences. The trackball used was the Kensington trackball which is designed with a big "ball" in the center of a plate. No wrist support was provided. Greater wrist extension and higher forearm muscle activity was observed with the trackball. They found lower muscular activity in the right trapezius muscles in both men and women, as well as lower shoulder elevation with the trackball. They found higher muscular levels in women, especially in the deltoid muscles, as well as greater outward rotation of the shoulders when using either input device. They hypothesized that this was because men tend to have broader shoulders and greater muscle strength than women. Unlike previous studies on the trackball, they did not find a decrease in productivity with the use of the trackball.


Laursen, B., & Jensen, B. (2000). Shoulder muscle activity in young and older people during a computer mouse task. Clinical Biomechanics, 15, Supplement No. 1, S30-S33.

Gustafsson, E., & Hagberg, M. (2003). Computer mouse use in two different hand positions: exposure, comfort, exertion and productivity. Applied Ergonomics, 34, (2), 107-113.

Karlqvist, L., Bernmark, E., Ekenvall, L., Hagberg, M., Isaksson, A., & Rostö, T. (1999). Computer mouse and track-ball operation: Similarities and differences in posture, muscular load and perceived exertion. Industrial Ergonomics, 23, (3), 157-169.

Special new half day and whole day rates for companies of all sizes. This is an excellent way to save you money and prevent injuries.

Ergovera can help you with:

  • Assessing and changing workstations.
  • Educating employees on risk factors and ways they can work more safely.
  • Recommending products (only if necessary).

Call Deidre at 831.335.8448 or send her a message now for more info about the class, rates and dates we could do the workshop at your site.

Copyright © 2002, Deidre Rogers and Ergovera Ergonomic Consulting. All rights reserved. Reuse in any form must be requested and granted in writing.

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