Newsgroups: comp.risks
X-issue: 10.13
Date: Thu, 28 Jun 90 14:11:52 EDT
From: henry@zoo.toronto.edu
Subject: Re: info on carpal tunnel syndrome (CTS)

>One point the author does not mention is that the "force-depression curve" of
>your keyboard may also play a role.  It is better to have a linear 
>relationship between force and depression...
>...  People have suggested that this sort of dynamic may
>aggravate or even induce CTS...

What was the incidence of CTS twenty years ago, when electric typewriters
routinely had non-linear force-depression curves?  Or before that, when
manual typewriters required far more finger pressure than any modern
keyboard?  Yet again, we have here a case of a "computer risk" that isn't
really new, and data from olden days could be very useful in deciding what
*really* causes it.

Data would be particularly useful because it's easy to construct an argument
that points in precisely the opposite direction!  Once you've pushed a
non-linear keyboard key "over the hump", you can relax pressure.  But with
a linear keyboard, you have to push all the way down, since you get no
"that's enough" feedback until the key hits bottom.

Some of this may be a risk not of nonlinear keyboards, but of lack of proper
training.  Pre-computer typing courses taught you to *strike* the keys rather
than *pushing* them, so your muscles were already relaxing when the key
bottomed out.  One side effect of the proliferation of keyboards is that far
more people are using them without formal training, or with training from
"touch typing" programs that teach you which keys to hit but don't teach
posture or hand position.
                                         Henry Spencer at U of Toronto Zoology