Keyboard and Mouse Position: The Geometry Behind Shoulder Ache

Ache on one side of the neck and shoulder is one of the most common desk complaints and one of the easiest to trace. It is almost always the mouse.

A keyboard is symmetrical and sits in front of you. A mouse sits out to one side, and reaching for it repeatedly pulls one shoulder forward and rotates the trunk a few degrees. Repeat that a few thousand times a day and one side of you does more work than the other.

Here are the four positions that matter, the published targets, and what each miss produces.

The four positions

1. Keyboard height, relative to your elbow. The keyboard surface should sit at roughly your seated elbow height, with forearms parallel to the floor. OSHA's guidance puts the upper arms close to the body with elbows between 90 and 120 degrees.

Too high lifts the shoulders. Too low rolls them forward and puts the wrists into extension over the front edge of the desk. Most people have this wrong because most desks are too tall, not because of anything they did.

2. Keyboard tilt. Flat, or tilted slightly away from you. Not toward you.

Every keyboard sold has flip-out feet at the back that tilt the far edge upward. Using them puts your wrists into extension, which is the position associated with pressure on the carpal tunnel. They exist because they make the key legends easier to read on a low desk, which is a problem you should be solving with the desk.

A negative tilt, where the front edge is higher than the back, keeps the wrist closer to neutral. Some keyboard trays are built to do exactly this.

3. Mouse distance from the keyboard. As close as it will go.

This is the one that matters most for one-sided ache. A mouse placed beyond a full-size keyboard with a number pad sits eight to ten inches further out than one placed beside a tenkeyless board. That is eight to ten inches of shoulder abduction, held, all day.

The fixes, in order of effect:

• Use a keyboard without a number pad, which moves the mouse in by the width of the pad.
• Move the mouse in until it touches the keyboard.
• Consider a trackball or a vertical mouse if the reach itself is the problem rather than the grip. What the vertical mouse research measured, and four models, covers the forearm side of that choice.

4. Wrist support, and what it is for. A wrist rest is for resting between bursts of typing, not for resting on while typing.

Planted wrists mean the hand moves by deviating at the wrist rather than by moving the whole forearm. Ulnar deviation, sustained, is its own problem. Use the rest in the pauses. A one-piece keyboard adds some ulnar deviation of its own, and a split keyboard is the design that removes it.

Position	Target	What a miss produces
Keyboard height	At seated elbow height, elbows 90 to 120 degrees	Shoulders elevated all day, or wrists extended over the desk edge
Keyboard tilt	Flat or tilted away from you	Wrist extension, which is the position that loads the carpal tunnel
Mouse distance	Touching the keyboard, or as close as possible	One-sided shoulder and neck ache, the classic mouse-arm pattern
Wrist rest use	Between bursts, not during typing	Sideways deviation at the wrist instead of forearm movement
Elbow position	Close to the body, not winged out	Sustained load on the upper trapezius on the mouse side

The test that finds the problem in ten seconds

Sit and work normally for a minute. Now, without moving anything, look down at your two elbows.

If one is further from your body than the other, that is your answer, and the side that is winged out is the side that aches. Nothing else on this page will matter as much as bringing that elbow back in, which means bringing the mouse in.

Second test: photograph yourself from the side while typing. If your wrists are bent upward over the front edge of the desk, either the keyboard is too high or its feet are flipped out. Both are two-minute fixes.

The number pad question

A full-size keyboard is about 17 to 18 inches wide. A tenkeyless is about 14. That three to four inches is pure mouse-reach, and for anybody with one-sided ache it is the single change that buys the most for the least.

The obvious objection is that you use the number pad. Two answers: a separate number pad placed to the left of the keyboard costs about $25 and removes the trade-off entirely, and most people who think they use it are doing so a few times a week.

This is a cheap experiment. Borrow a compact keyboard for a fortnight before deciding.

Why the desk edge matters more than the keyboard

A detail that gets missed: the front edge of the desk is a hard surface your forearms rest against, and on a lot of desks it is a square edge.

Two consequences. A sharp edge concentrates pressure on the underside of the forearm, which is uncomfortable and, over years, is associated with contact stress complaints. And an edge you rest on becomes a pivot, so the hand deviates around it rather than the whole arm moving.

The fixes are cheap. A rounded or waterfall front edge is a genuine feature to look for on a desk, and where you already have a square one, a length of adhesive foam edging costs a few dollars. The better fix is to stop resting there at all, which usually means the chair is too low or the armrests are set too far down.

This is also the argument for a keyboard tray beyond its height benefit. A tray puts the keyboard in front of and below the desk edge, so your forearms are over open air rather than over the edge.

The mouse itself, briefly

Three properties matter and they are not the ones marketed.

Size relative to your hand. A mouse too small for your hand is gripped with the fingertips, which is more tension than a palm grip. A mouse too large drags the wrist into extension. Measure your hand from the crease of the wrist to the tip of the middle finger and compare it against the published length of the mouse, which most manufacturers do publish.

Sensor sensitivity. A higher DPI setting means less physical movement for the same cursor travel, and less physical movement is less shoulder work. Turning the sensitivity up one notch is free and it reduces the total distance your arm covers in a day by a surprising amount.

Button force. Cheap switches need a firmer press, and a firmer press repeated thousands of times is a real load on the finger flexors. This is the one specification almost nobody publishes, which means it has to be judged in person.

Where this fits in the order of fixes

Hand position is the third geometry, and it moves when the other two move. Fixing it first is why people re-fix it three times.

The order that works is desk height, then screen height, then hands. The desk arithmetic sets the surface your hands work on. The screen numbers decide whether your neck is flexed. Only then is it worth spending time on where the mouse sits, because both of the earlier fixes change it.

And underneath all three is the chair. If your feet dangle and your pelvis has rolled back, your whole trunk is rotated slightly forward and every arm measurement is taken from a moving reference point. Nine minutes with the levers comes before any of this.

Questions people actually ask

Should my keyboard be flat or tilted?

Flat, or tilted slightly away from you. The flip-out feet at the back of almost every keyboard tilt the far edge up, which puts your wrists into extension. They exist to make the legends readable on a desk that is too tall, which is a problem better solved at the desk.

Where should the mouse go?

As close to the keyboard as it will physically sit, at the same height. Every inch further out is shoulder abduction you hold all day, and that is the mechanism behind almost all one-sided neck and shoulder ache at a desk.

Does a smaller keyboard help shoulder pain?

Frequently, and it is the cheapest structural fix available. Dropping the number pad moves the mouse three to four inches closer to the body. If you genuinely need the number pad, a separate one placed on the left keeps both.

Are vertical mice better?

They change forearm rotation rather than reach, so they address a different complaint. If your problem is wrist or forearm discomfort, a vertical mouse is a reasonable thing to try. If your problem is one-sided shoulder ache, moving the mouse closer matters far more than its shape.

Should I use a wrist rest?

Between bursts of typing, not during. Resting the wrists while typing makes the hand move by deviating sideways at the wrist rather than by moving the forearm, which trades one problem for another.

Sources

• OSHA Computer Workstations eTool, working postures section, for elbow angle and upper arm position.
• OSHA guidance on keyboards and pointing devices, for keyboard height, tilt and input device placement.
• OSHA guidance on wrists and hands, for neutral wrist positioning.