Input devices: a usage-driven approach


Some of these accessories are valuable, but a lot of them are gimmicky, if not downright dangerous.
Pascarelli & Quilter in Repetitive stress injury

I am writing this essay to summarize my years of experiments with input device design. My interest is born out of a long-lasting typing injury, but I have no formal training in ergonomics. I hope to provide a critical and realistic view of what can be done to improve input devices. The goal of course is to fundamentally reduce the strain on hands and arms when using the computer. It is actually possible, I believe, to work in a fashion that is dramatically easier on hands, arms, and shoulders. There is no miracle: it involves (1) speech recognition and mastery of a system of voice commands (2) use of a reduced-impact pointing device that may be shoved around by one or two hands, and (3) a foot pedal arrangement.

Neither of these techniques are commercially available; nor have they been tested in long-term experiments by others—the expensive and only way of establishing claims of ergonomic superiority. However, the proposals I present have been subjected to my own daily usage for several years. They represent but a fraction of ideas and commercial products that I have attempted to use long-term.

The main point of this essay is that input device design is very difficult, even though there are often simple explanations why a design is potentially injurious. I will give several examples of input device designs that are superficially appealing, but seemingly devoid of functional qualities that make them usable in ways that fundamentally reduce physical stress. Rather, by their very construction, some alternative designs hold the potential of being more harmful then the traditional designs they are intending to replace.

The patent literature is brimming with input device ideas. Engineers, doctors, and lay people have investigated mouse surface curvatures, twistings of the keyboard, wearable gizmos, etc. These initiatives apparently have had little impact in reducing pain and injury from computer use.

Even the popular "ergonomic" split keyboards have not been shown to have any health benefits; a proof, if possible, would involve long-term studies involving thousands of individuals. The theory that these keyboards are easier on body because they involve less “deviation” of the hands relative to the forearm is plausible. But maybe more plausible is the opposite hypothesis: what matters is only how you use the keyboard. Moreover, the opposite hypothesis argues that since the standard keyboard is smaller it better allows your hands to manipulate the mouse and to find a resting position. So, it is already clear that the so-called “ergonomic” keyboards are “ergonomic” in name only; they represent another compromise among a host of competing design constraints.

This kind of analytical thinking about various stresses on the body incurred by use of devices is important to anybody who is struggling with pain from computing, since it is one way of raising body awareness. This is especially true since the innumerable negative experiences with “ergonomic” equipment go unreported. Whether it be a speech recognition program or an especially “ergonomic” mouse design, the technology is usually disappointing. The defeat is not broadcast to colleagues and friends.

Why do keyboards and mice hurt people? Nobody seems to really know. At a cellular level, the processes behind CTD remain a mystery, although it is believed that inflammation is not a necessary component, see for pointers to medical literature. At the functional level, it remains unproven that repetitive motion is to blame. For example, another functional culprit could be the constant stress the body is experiencing when near the devices.

To understand this, think about replacing each key on the keyboard and each button on the mouse with a little hot plate glowing red. If you were working next to such a monstrous instrument, then you would condition your limbs to be constantly adjusting themselves so as not to touch any of more than one hundred hot plates. The point is, of course, that even when keyboard and mouse do not posses thermal properties, your body must be conditioned exactly the same way.

The mouse is particularly bad, since the hand tends to ride it. Consequently, fingers must be forced upwards to not press the hot plates.Arrow showing static    stress force when using mouse Extensor muscles, the arms' weakest ones, are continuously struggling to keep this unnatural balance even if the brain thinks that the hand is at rest. Interestingly, preschool kids struggle quite a bit with this likely injurious principle. Whereas they may easily learn to type out their own name on the keyboard, it may take several more months for them to learn to hold the mouse without pressing the buttons—an indication that the mouse is anything but natural.

In my judgement, there are three areas where new thinking may lead to less pain when using a computer. For the keyboard, there is only little room for improvement—still I have some modest ideas, see keyboard. In contrast, the mouse may be an essentially harmful device that cannot be improved within its traditional design constraints—see my proposal in mouse for a different concept. Finally, I suggest how foot pedals can very effectively complement a keyboard or speech recognition for repetitive tasks in foot pedals.

My opinions and proposals are the result of a decade of personal experimentation and observation. That's why I call this overview a "usage-driven approach". The information I offer here should not be construed as advice. I do not know whether my observations are generally applicable. If you have pain, then go see a doctor. The only recommendation I offer to others with typing or mouse injuries is to look in the excellent book Repetitive strain injury by Emil Pascarelli and Deborah Quilter (John Wiley and Sons, 1994).


I doubt they were built for hand safety: mice inherently strain the hand...
Pascarelli & Quilter in Repetitive stress injury

The mouse is a spoiler. Whenever you put your hand on it, you stress your body. If for a moment you forget to apply a lifting force to your fingers, then buttons are immediately activated. Consequently, your body must work constantly with shoulder, limb, hand, and finger positions to not press buttons. Unless, of course, you take your hand away from the device. Something the size and shape of it discourage you from doing. The lighter the mouse buttons are to depress, and the bigger they are, the more static force is needed to prevent accidental mouse clicks. Thus, curiously, there may be a direct relationship between how "ergonomic" the mouse is and how harmful it is.

The keyboard is much more forgiving in this regard. It is natural to rest the hands in front of the keyboard as soon as they are not in use. But given that the mouse inherently forces an unnatural, constant muscle response, I believe that researching mouse curvatures alone is an exercise in futility.

The buttonless mouse

Instead, mouse buttons must be entirely removed from the pointing device itself. This is not a radical idea: on laptops, the pointing device (stick or pad) is separated from the buttons. Also, the new mouse feature called a scroll-wheel should be moved to the keyboard. The mouse is the last place another function should be placed. Finally, the proper mouse size is less than the standard one.

Now what are the consequences? The series of pictures below illustrate five of numerous ways a small, buttonless mouse can be manipulated. (The mouse shown has actually its buttons disabled.) Most of these poses are not possible with a conventional mouse unless various fingers are counter-balanced to not depress the buttons.

One-handed finger ride
One-handed finger ride
One-handed side grasp
One-handed side grasp
One-handed thumb ride
One-handed thumb ride
Two-handed shove
Two-handed shove
Two-hands semi-ride
Two-hands semi-ride

These pictures indicate how an appropriate shape allows the the mouse to be manipulated by just putting a part of the hand on top of it, while the side of the hand still rests on the table. This easy-on-off principle encourages the hand to rest on the desk, not on top of the mouse. It is still possible to have the hand ride on top of the mouse—while the hand gets gets a lot of support both from the desk, because the mouse fits in the palm of the hand, and from the mouse itself, because of the lack of buttons. Note that to use the mouse in such varied ways, where hands are given plenty of resting areas, more space is needed than what is usually available on a keyboard tray. That's why I believe that reducing keyboard size, or getting rid of it by combining speech recognition and foot pedals, is very important.

And where do the buttons go?

The buttons may go on either side of the keyboard or be foot activated. In keyboard, I propose how scrolling functionality and mouse buttons can be conveniently combined on a keyboard. This arrangement will not slow you down: as one hand is leaving the keyboard to locate the mouse, the other slides to the side where the buttons are easily found. And, in foot pedals I consider available and future foot switches.


I believe that it would be interest to carry out controlled trials of simplified, buttonless mouse designs. If the design of the mouse impacts its injury potential, then a study is more likely to demonstrate this effect the larger it is. The removal of buttons may offer the best chance for obtaining such an effect.


Pointers—self taught typists who hunt and peck instead of touch-type—...are the least likely to be hurt from their style.
Pascarelli & Quilter in Repetitive stress injury

From bitter experience, I don't believe that the keyboard can be improved much. Three times, and without success, I have built whole keyboards from scratch. Nevertheless, there are a few changes I would like to see done to the keyboard:

Why keyboards have gotten less ergonomic

For modifier keys, such as Ctrl and Shft, ergonomicity has declined. When they are widely spaced apart Widely spaced        Ctrl and Alt keys as on keyboards made in the mid '90s, these keys can be depressed easily with the side of the hand or with the outer side of the curled-up little finger, all while the thumb is facing upwardsPressing modifier       keys without strained uses of fingers. In this way, the strenuous finger work usually associated with chording is avoided. Unfortunately, modern keyboards suffer from extraneous OS-specific keys that prevent this technique from being used. (Except if these keys are uprooted or lowered.) On a flat keyboard, such as on a notebook computer, fingers are even further restrained by the flatness from hitting keys in a variety of ways—something that is likely an ergonomic drawback.

A keyboard layout proposal

A keyboard layout following these ideas mentioned above is suggested in Figure 1. Below it's shown (left) how a large, comfortable belt may be placed on the left side of the keyboard, along with mouse buttons; the side of the hand (right), not the fingers, securely moves the belt.

These ideas and the figure below are from AT&T Technical Disclosure A keyboard design by Nils Klarlund.

Keyboard layout
Click for bigger picture

Foot Pedals

One of the most popular misconceptions about computer work is that it is an “easy” activity, when in fact it is quite strenuous for your hands and arms.
Pascarelli & Quilter in Repetitive stress injury

Obviously, foot pedals cannot replace the keyboard. But it is intriguing that many of us use our strongest limbs to control safety-critical pedals while going to or from work, while the same limbs stay underemployed under the desk all day. The problem is that using just two a three pedals as in the car will not cover enough of repetitive work to make a difference. For example, even processing incoming e-mail requires at least five keys (next message, previous message, scroll down, scroll up, and delete message). And, naturally, typing with our feet must be considered a hopeless task for most of us.

Speech recognition offers an excellent alternative to typing, even as it seems hopeless at repetitive work. Saying "page up", "page up", "page down" to browse through a web page speaks for itself. So, maybe the combination of speech recognition and foot pedals is the combination that will effectively offload the hands?

This was my thinking when I started using speech recognition six years ago. Initially, I used five or six foot switches glued to a wooden board. Through several iterations of pedals arrangements, I arrived at a basic layout that can be seen in the photos below.

(For a technical disclosure, see US5889510 Foot-operated keyboard device)

In this design, each foot may operate seven front keys placed around the sides and front of the foot. Most common keys are present: the arrow keys, enter, backspace, space, and tab. In addition, left and right mouse buttons are present (see mouse why this is important). Also, there are an undo key and three keys important to speech recognition: repeat last voice command, correction, and microphone on/off. All of these keys are commonly used. But 14 keys don't suffice. So, other common functions such as "page up", "skip over left word", "change window focus", "go to the beginning of line" and "go to end of document" are activated through a combination of a front key and one of two modifier keys behind the foot. The idea is to step forward on a front key with one foot while the heel of the other presses the modifier. The modifier pedals are two-level switches, so altogether the keyboard offers 14 * 5 = 70 foot-activated functions. A video (streaming Windows Media) (mpeg-1 (28Mb)) of a version of this keyboard is available.

The design shown here is crude; it is possible to devise much better working key shapes.

I have used this design for four years. In my experience, the combination of speech recognition, based on the editing language ShortTalk, buttonless mouse, and foot pedals is significantly more efficient than the keyboard + mouse combination. This efficiency is important: it is the driving force for using the combination. It is extremely difficult not to work in one's old ways if the new ways are not superior.

Skeptical Remarks

The public should be skeptical about claims of ergonomic superiority...
Pascarelli & Quilter in Repetitive stress injury

Although some “ergonomic” accessories or devices may fit certain people, I believe that there are easily argued reasons why most of them may not work or may even be harmful. These opinions are examples only, offered to stimulate critical thinking.

Forearm rests

These often elaborate mechanical contraptions support your forearm even while in motion over the keyboard. But a fundamental misunderstanding may be a play here: the muscles of the forearm lift a heavy object, the hand, that is not supported by forearm rests. So, the full weight of these long, bony structures still have to be born by the forearms. And, perversely, the forearm rests may make it cumbersome to place the arms in a position where the hand and forearm can truly rest, because it takes quite an effort to get in and out of these devices. As a result, the strain on the forearms may be very significantly increased by using forearm rests.

Contoured keyboards

In these keyboards, the majority of the keys are placed inside a depression along a curvature. There is one depression for each hand, so that the keyboard may look like two bowls in a frame. By matching the movement patterns on the fingers—the theory goes—these keyboard are easier on the body. But precisely thanks to this property, the keyboard will force the hands into hovering in a specific position in space above it. In contrast, a flatter layout gives superior flexibility for striking the keys.

Microswitch keyboards

This paradigm stipulates again that motion is at the heart of injury. The keyboards accommodate each finger in an individual fixed area or well in close proximity to tiny switches. Then minuscule movements of fingers active switches. Phenomenal typing speeds are achievable. I got the feeling when using a design of my own of getting a kind of direct feed from brain to computer. But again, there is a fundamental misunderstanding at play if the aim is to reduce physical strain: the body must continuously adjust the position of all fingers so that they don't touch the switches. This compensation includes maintaining positions of hands, forearms, not to say the whole body. Again, the conventional keyboard is superior. With it, the hands are free all the time, except for the moment of strike, to rest or to hover over the keyboard.


It has been suggested that using a pen on a tablet is more ergonomic than using a mouse. Unfortunately, there is a condition called writer's cramp that has been known for hundreds, if not thousands of years, and it is likely to affect the tablet user as well. Holding a pen puts static load on the whole upper body, so that the pen is not dropped and does not touch the tablet when not in use.

Touch pads

So what about not holding anything at all? The touch pad offers such a solution, but as most people have experienced, this technology does not work to well either. The cramped space is anything but natural for tracing the movement of the cursor by using the index finger. Even if the touch pad was big enough that the whole hand could rest on it, it would still induce static stress: the hand must be turned so that the index finger does not touch the surface, whenever the cursor is not moved.


There are good things be said about trackballs: the hand may rest next to the device while the cursor is not being moved. Moving the cursor can be done with the thumb or side of the hand. Unfortunately, most trackballs that are on the market have large, easily depressed buttons surrounding the ball. This "ergonomic" look probably have the opposite effect: the hand constantly must balance itself to not touch the buttons whenever near the device. So, such trackballs may be as harmful as ordinary mice.

So, what helps?

I believe that no tinkering with keyboard or mouse design will lead to products that are radically less stressful on the body. Marginal improvements, perhaps along the lines I've suggested, may be possible. Ergonomic manuals consistently state that there is one way only to effectively address severe cases of overuse syndromes: complete and total cessation of the physical activity that led to the problem. Sometimes this cessation must be permanent, often implying a loss of ability to work. Finger and hand work must be avoided in any form that resembles the injury-causing way of working.

An approach to reduce physical impact might be: type with only the strongest fingers (thumb and index) and move a mouse by pushing it with two hands resting on the desk or keyboard tray. Such behavioral techniques may offer far greater potential for reducing injury than any changes in device design. But their use may also lead to further injury, given that they represent a very different approach than that of complete rest. For lesser injuries, other techniques are possible as is discussed in books on computer-induced injuries.

In conclusion, I believe that avoidance and technique are more important than device design. Avoidance can be achieved by a combination of speech recognition and foot pedals. I doubt that there are any other ways that are comparable in efficiency.

My Own Setup

Here are some information about how I put my work environment together. For a picture of my workspace, see User interface summary.

Foot pedals

It is difficult, if not impossible, to buy appropriate foot keyboards. Foot switches that just float around on the floor are a bad idea. Your feet won't be able to find them—and using them frequently may induce cramps in calf muscles. Foot switches should be mounted on a foot rest. A Y-key dual keyboard adaptor (from allows two keyboards to be used together. Also, I believe that USB keyboards can be used in parallel. In any case, individual foot switches can connected to the soldering points under each key on a second keyboard. It's easiest to work with a keyboard equipped with mechanical switches, since capacitive switches may require the addition of a capacitor for each key. The construction of a keyboard like the one shown probably can be done in a couple of days by somebody with electronic and woodworking skills.

Buttonless mice

Under Windows 2000 and XP, it is easy to make several mice work together. Personally, my favorite "ergonomic" mouse is a 10 dollar device from Sakar International (Model #77452, Iconcepts). It is small so that the hand does not have to struggle mounting it, and it is not too rounded. I have disabled the mouse buttons by sliding two thin slices of rubber in the gap between the button and the case. A better alternative is to reshape an optical mouse, by peeling off the upper casing; a better surface for grasping the mouse can then be built out of epoxy or modeling clay. Electrically, an ordinary foot switch or an extra key mounted on the keyboard over a micro switch may be used to short-circuit the two contact points of the micro switch serving a button inside the mouse. Thus, with relatively modest soldering skills, one can connect a mouse button switch via a second mouse (that is used solely for this purpose). Under Windows 2000 and XP, it is possible to press the button of one mouse, while moving the other mouse, to achieve the effect of dragging. This is not possible under some other operating systems, including Windows 98 and Me.

There might be easier ways to obtain a buttonless mouse—I have not investigated alternatives.

Wireless microphone

I like the design of the wired Emkay D-loop microphone. It is very comfortable to wear, and the microphone stays in place. Unfortunately, I have not been too impressed with the wireless consumer solutions that I've tested. They do not provide a clean signal. Instead, I use a Shure LX wireless system. The microphones that Shure provides come with elastic bands that wrap around your neck. This a great solution for aerobics instructors—but an unworkable solution for speech recognition: you can't move your head without the microphone moving in front of your mouth. Instead, I have connected an Emkay D-loop microphone to the mini-XLR connector. The details are: connect shield to pin 1 and short-circuit pin 3 and pin 2 (which carries 5 V) and connect the hot wire (red) or pair of hot wires (red and white) to that short (inspiration for this operation is the diagram found at To accomplish this wiring, I had to open the female mini-XLR connector. To my knowledge, there is no mini-XLR to mini phone plug connector on the market. I hope Bluetooth technology will be able to replace my LX system.


I used to use an IBM keyboard without numeric keypad to gain space. This excellent keyboard has mechanical switches and widely spaced Shft, Ctrl and Alt keys (IBM part no 1397681). It is not made anymore. My current keyboard is different, but since finally I am able to largely not use it, its design is not important.


In my experience, Pentium III processors under 1 GHz are inadequate for speech recognition based on the NaturallySpeaking dictation system, now produced by Scansoft. The last year I have been using a AMD-based processor (Athlon 1.4 GHz) with extremely nice results: response time for short utterances is very quick and the system altogether has been very stable. Half a Gb of RAM is required and sufficient.

By Nils Klarlund. Copyright ©Nils Klarlund, 2002.
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