Cornell University Ergonomics Web
DEA 3250/6510 CLASS NOTES
Brief History of Keyboard design:
Recommended keyboard worksurface height for typewriters
was the 26" typing return (plus the height
of the keyboard). At this height shoulder muscle tension was lessened, and the
keys were stepped so that wrists could remain flat and neutral.
As hands go into typing position, hands have a tendency to go into ulnar deviation, especially with a wide person. First split keyboard design is often attributed to Klockenberg (1926 in Germany), but actually a split keyboard was used in a typewriter built in1886 (Louis Crandall, Syracuse, NY). Etienne Grandjean (Swiss ergonomist) developed a split keyboard in 1976 which supported the whole forearm (curved keys as well). Split keyboard - assumption is that the problem for discomfort is only ulnar deviation.
How to tell ulnar deviation - if looking down on hand if the skin is folding on the outside edge where the hand meets the wrist, there is ulnar deviation.
Split keyboard designs do not necessarily
address other wrist deviations. Wrist Extension - Intra Carpal Pressure (ICP - measured in mm of mercury), starts to rise
quickly as hands move into wrist extension above 15 degrees..
In the seventies - there was no idea that wrist extension would be a problem and on older conventional keyboard you could rest your hands on the keys without activating them. This is less true of modern light touch keyboards, and wrist extension is a major problem.
How to tell wrist extension - if looking down on hand if the skin is folding on the top of the hand at the wrist, there is undesirable wrist extension.
QWERTY keyboard layout:
DVORAK keyboard layout (1936):
Maltron Layout (UK, 1970's) - uses cupped/dished key design:
Virginia PolyTechnic Institute (VPI), Prof. Ed Kroemer - mid-60's tested split keyboard designs and published results in Human Factors journal.
Early 1990's - Apple split keyboard - also separate numeric key pad to go on either side (too big and bulky) - now defunct.
Some other split designs:
Risk of musculoskeletal injury depends on :
Some vertical split keyboard designs place the hands
Wrist Rests - low-cost, often useless, even dangerous devices.
Most wrist rests don't work effectively at all because people rest their wrists on them, which puts pressure on the carpal tunnel and restricts circulation to the hands..
Wrist splint - these should not be used for any sustained time period if they put the hands into wrist extension - flat is better.
Arm supports (onto work surfaces) - not recommended because they can compress the flexor muscles.
Palm Support - recommended if they provide support to the thenar and hypothenar eminences (fleshy areas below thumb and little finger).
Negative slope keyboard trays - reduce keyboard
angle by tilting a keyboard tray away from the user which puts the keys closer
to 0 degrees to the hands.
People have very similar typing styles even when keys presented a different angle,
and typing performance isn't disrupted. A very effective solution.
Some claim that keyboards may become obsolete and replaced by voice, but this is unlikely because:
Many design force hand into wrist extension, and some force this into ulnar devation as well. Mouse keys need ~ three times as much force as keyboard keys. Position of mouse determines postural risks - keep mouse close to body
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