Articles

Abstract

In this paper, it is shown that a teddy bear skin spongy mouse is a better option than a conventional plastic mouse design and that a portable arm rest mouse pad platform is far better than the conventional mouse platform placed to the side of the keyboard tray. Both designs help reducing arm abduction and related discomfort, pain, fatigue and soreness. Ten people voluntarily participated in the task and completed a series of psychophysical questions (Borg RPE [Rate of Perceived Exertion] Scale was used to evaluate). Results indicate a much smaller perception of pain and discomfort on palm and wrist with the spongy mouse rather than conventional designs, especially to palmar aponeurosis and ulna muscles. The mouse pad greatly reduced all the pressure points of hand and added comfort on wrist and forearm (e.g. flexor retinaculum (FR) and palmaris longus muscle area).

Index Terms— Awkward posture, Brog RPE scale, Carpal tunnel syndrome (CTS), Electromyogram (EMG), Ergonomics, fatigue.

I. INTRODUCTION

With the advent of graphical user interfaces (GUIs), work on video display terminals increasingly involves a pointing input device, which is used with 30 to 80 percent of computer activity. Along with this increase, there has been increase in the incidence of work-related musculoskeletal disorders [1] and blood clots at the wrist.

Several research studies have shown that extremes of flexion/extension and radial/ulnar deviated wrist postures beyond 20� raise intracarpal pressure, which increases the risk of wrist and hand injury. In a study conducted by Alan Hedge "Rapid Upper Limb Assessment (RULA) scores for wrist postures were poor for all the experimental mouse positions. Subjects reported that discomfort in their mousing hand was associated with poor wrist posture. The vertical location of the mousing surface and the provision of a wrist support also affect wrist posture." [2].

A conventional mouse is made for a general hand with a specific holding posture. But if every person's hand shape and size is different and hence the way of holding, why should the mouse be the same for everyone? The posture in which a person sits and holds the mouse also matters. Usually we give little attention to these problems and are often caught by carpal tunnel syndrome (CTS) [3]. The present study tries to eliminate these two problems.

A. Problem of mouse design

Many ergonomic mouse designs are available in the market, such as the tiny mouse, rubber-coated mouse, extra-large mouse, hand-shake (quill) mouse, thumb-operated mouse, force feedback mouse and others of various hand postures and sizes [4][5]. Yet there is not a single mouse that can take the shape of all. In a developing country a single desktop computer is shared between a number of persons. The users' ages can vary from a 5 to 80 years. A conventional mouse is not made to accommodate this range of palm design. Even for the average adult-sized person, the way one holds the mouse differs. This could lead to wrist extension and effect the flexor retinaculum area (transverse carpal ligament). Holding a large mouse tightly may create pressure at the ulnar nerve (hypothenar muscles). Hence, there is a need of a mouse that takes the shape of your palm and fits into it exactly the way it should be. A spongy flexible mouse can solve the problem. Spongy doesn't mean squeezing the mouse tightly but instead having a fair grip and soft touch. Squeezing any mouse tightly between the thumb and little finger will again stress your wrist [3].

B. Problem of awkward posture

Desktop computers were first placed on simple tables, which evolved into ergonomic tables in which the keyboard and mouse tray were lowered. Yet that didn't solve the problem of eliminating pressure points, which form when the whole hand rests on the wrist. Many of us don't notice that our forearm is in air, until we develop a pain in the palmaris

Fig. 2. Stuffed, soft mouse with a teddy bear skin cover.

longus and other forearm muscles. Nor does the conventional mouse platform at the side of a keyboard tray stop the shoulder abduction, ulnar deviation problem. The latest ergonomic mouse tray designed at Cornell University Ergonomics department ensures that your arm, wrist and hand remain in a straight line [6]. Yet very few people go for exact ergonomic tables. For developing countries one problem remains because of which people neglect this matter: and that is money. From where will you purchase an exactly designed ergonomic chair and table with a proper mouse tray? Who will take pains in replacing their older well furnished computer table? A cheap, portable armrest mouse pad can solve this problem. This mouse pad can be mounted on the armrest of any chair. This pad also ensures that the arm, wrist and hand are in straight line, and gives rest to your forearm. wrist rest should not be used as it doubles the pressure inside the carpal tunnel [3].

II. METHODS

A. The Mouse

The original design proposed is in Fig. 1. For testing the concept, an ordinary optical mouse was taken, the outer body was cut down, and the circuit was covered with polythene for protection. Reliance artificial fiber was chosen as a stuffing material. It has an excellent tendency to revert back to original position with almost nil fatigue effects. After stuffing the sufficient amount of material so that it becomes spongy, it was covered with a cotton cloth and sealed by gluing it with "Fevi-Quick" glue. Velcro tape was pasted on the cover, so that we can change and wash the covers. It is shown in Fig. 2.

Fig. 3. Armrest mouse pad design

Ten volunteers (8 male and 2 female) of age group between 20 to 27 years were seated and given the task. All were IT students of Indian Institute of Information Technology, Allahabad, India. Subjects were free from any musculoskeletal disorders. They were the users of a normal optical mouse. Subjects were given the task to play Unreal Tournament (for working in the excited state), play Age of Empire (For working in strategic and low pressure state), Minesweeper (for normal strategic state) and do their daily jobs for five days. Each day, subjects were made to fill a psychophysical questionnaire assessing their perceived musculoskeletal loading, comfort before and after using the mouse.

Fig. 1. Spongy Mouse Design

B. Armrest Mouse pad

Acrylic fiber sheets of 5mm width were chosen as they are very durable, strong and light. The sheet was cut as per Fig. 3. Since the mouse doesn't work on purely smooth surfaces, two different materials (a normal plastic mouse pad, cotton cloth) was covered and tested. The cloth was found to be the better option. To attach it on any armrest of a chair, strips of Velcro tape were used and a long tape was covered at the back of the handle to ensure stickiness (Fig. 4). Five of the 10 subject worked with a conventional mouse tray placed at the side of keyboard and 5 of them on a table where the monitor is kept. Subjects were asked to use this pad for a week. Similar psychophysical questions pertaining to pain and comfort level were asked before and after the use of this pad.

The questions were posed on a visual analog scale modified from the Borg RPE (Rate of Perceived Exertion) Scale. [7]. A 9-point scale was used (1-10) designed to quantify difficulty, pain, discomfort, fatigue and soreness felt before and after the use of normal and new mouse design. As an example, the verbal anchors on the scale for difficulty ranged from "very, very easy", to "easy", to "somewhat difficult", and finally to "very difficult". Since levels of exertion for the given task are low, I envisioned the modified Borg RPE scale would provide the necessary resolution to observed differences between each test condition.

III. RESULTS AND DISCUSSIONS

Fig. 4. Portable ergonomic mouse Pad design

Fig. 5 Blood clotting due to extensive use of mouse

A. The Mouse

Research studies show that the wrist extensor muscles have the highest level of activity and shoulder a relatively low [8]. Extensive use of a normal optical mouse continuously for long hours results in a blood clot at the wrist portion as shown in Fig. 5.

This occurred due to wrist extension, an improper way of holding the mouse. After introducing the spongy mouse, which fits into your palm, and takes your hands shape, the blood clot was reduced and subjects reported extreme comfort in their palms. But if you use it by holding tightly, squeezing it between thumb and finger, you get pain at flexor retinaculum portion. As far as comfortability is concerned the teddy bear skin reports the problem of grip holding. It was somewhat frictionless and slippery due to improper alignment of hairs, but the problem was solved by proper positioning and aligning the hairs.

Fig. 6. Subjective report of mouse design before use


Fig. 7. Subjective report of mouse design after use

B. Armrest Mouse pad

Fig. 6, and Fig. 7, shows the chart pertaining to questions asked related to comfort level.

Alan Hedge and Greg Shaw conducted an experiment on the "Effect of Mouse Position on Shoulder Muscle Activity" using electromyography (EMG) activity in the deltoid (shoulder joint muscle) [9]. Their experiment shows that a 10 degree of abduction angle made by shoulder is the position of minimum comfort. A conventional flat mouse tray beside the keyboard forces you to make an angle of 50 degrees, much greater than the 10 degree level of comfort. Hence arm abduction can be reduced if we design a correct location for mouse placement.

Fig. 3, shows the design of an ergonomic armrest mouse pad. Fig. 9, (can be seen on the printable version only) shows the results of the questionnaire. It also helped reduction in blood clotting, forearm pain problem as in this posture; pressure points will not be created. In normal usage of a conventional mouse platform, the whole arm is in air, and only the palm and wrist areas rest on mouse, creating abduction in the arm, wrist injury, and carpal tunnel syndrome (CTS). But here, this can never happen as from elbow to fingers, the arm is touching the pad.

The mouse pad material used was a cotton cloth since on pure smooth surfaces, the optical mouse does not run properly. The cloth mouse pad was found to work better than a conventional plastic pad.

Fig. 9. Subjective report on mouse pad design after use

IV. CONCLUSION

The results are in favor of both the designs — spongy mouse and arm rest mouse pad. Due to improper alignment of hairs a frictionless problem was experienced in the beginning, but after alignment it proved to be better then the conventional mouse. Simultaneously the sample size of volunteers participated was small, but its exhaustiveness solved a basic and important problem. Further design analysis can be done on other mouse shapes and covers such as an acupressure mouse, mouse with different heights of bumps, flat mouse, finger-fitted glove mouse, etc.

V. ACKNOWLEDGMENT

The author would like to thank his friends and the volunteers for participating in work analysis and study.

VI. REFERENCES

[1] Jack Tigh Dennerlein, and Maria Yang, "Perceived musculoskeletal loading during use of a forcefeedback computer mouse," 1999 Meeting of the Human Factors and Ergonomics Society (HFES) Houston, Texas.
[2] Alan Hedge, Timothy M. Muss. and Marisol Barrero, "comparative study of two computer mouse," Cornell Human Factors Laboratory Reports, url: http://ergo.human.cornell.edu/Pub/HFlabReports/MouseRep.pdf
[3] The American Academy of Orthopadeic Surgeons, tips on prevention of Carpal Tunnel Syndrome (CTS). url: http://www.pl.net/9.3health/precar.htm
[4] Quill Mouse url: http://www.quillmouse.com, Thumb Mouse url: http://www.fentekind.com/ergmouse.htm, Force Feedback Mouse url: http://www.amazon.com/exec/obidos/tg/detail/-/B00001W01Z/104-1885431-8540730?v=glance
[5] Other Mouses: http://www.dansdata.com/ifeel.htm, http://www.logitech.com/index.cfm/products/productlist/US/EN,crid=19, and Google web search.
[6] Ergo Tips on Cornell university website url: http://ergo.human.cornell.edu/ErgoTips2002/home.html
[7] Rate of Perceived Exertion (RPE) scale information, University of Waterloo, Canada url: http://ahsmail.uwaterloo.ca/kin356/rpe/rpe/rpe.htm
[8] Jack Dennerlein, Maria-Helena DiMarino, Ted Becker, and Peter Johnson, "Wrist and shoulder muscle activity changes across computer tasks", HFES 46th Annual Meeting September 30 - October 4, 2002 Baltimore, MD USA.
[9] Alan Hedge and Greg Shaw, "Effect of Mouse Position on shoulder Muscle Activity," Dept. DEA, Cornell University, April, 199, URL: http://ergo.human.cornell.edu/AHProjects/EMGPaper1.pdf.

Author information:
Bhaskar Gupta
Indian Institute of Information Technology, Allahabad
H.No. - 7179, Sector- B. Pocket - 10
Vasant Kunj, New Delhi. India - 110070
Email:[email protected]
Phone: (M) +91 9839188616. (Res.) 91 11 26890063

Source: Ubiquity, Volume 5, Issue 30, Sept. 29 - Oct. 5, 2004, http://www.acm.org/ubiquity/