Author Topic: Interesting scientific study - ideal slope, opening angle (tent), height  (Read 4398 times)

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Offline daneb

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"The effects of keyboard slope on wrist extension, forearm pronation and elbowheight were mixed. On the plus side, the 8 degree slope led toa lower elbow height. On the minus side, it tended tomore wrist extension and forearm pronation. The -8 degree slope led to the reverse effects. Slopes in the mid-rangeof those tested, -4 to 0 degrees, provided the least wrist extension, forearm pronation and lowest elbow height. The effects of keyboard opening angle were also mixed.The 18 degree opening angle led to the least ulnar deviation and wrist extension, but also produced the most elbow separation (i.e. shoulder abduction) and forearm pronation. The mid-range opening angle, 15 degrees, may provide the best balance between reducing ulnar deviation while not causing greater elbow separation or forearm pronation."

Height of keyboard is ideal 4cm above elbow position.

 (opening angle = tent angle)

See https://www.researchgate.net/publication/24222026_The_effects_of_split_keyboard_geometry_on_upper_body_postures


Offline daneb

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Re: Interesting scientific study - ideal slope, opening angle (tent), height
« Reply #2 on: Sun, 25 November 2018, 10:46:41 »
I would not say they did this wrong, but that they hold one specific variable /table height/ as static (and varying other variables). Which is legit and normal methodological approach.

But of course, with varying height (of table, sitting position etc) they could obtain more broad picture.

Offline RominRonin

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Re: Interesting scientific study - ideal slope, opening angle (tent), height
« Reply #3 on: Sun, 23 December 2018, 15:55:07 »
And speaking of pictures, this post could do with a few to illustrate the findings.  ;D

Offline RominRonin

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Re: Interesting scientific study - ideal slope, opening angle (tent), height
« Reply #4 on: Tue, 25 December 2018, 01:16:37 »
Look what I found:


From the source: "Conventions for rotation of keyboard halves. α = slope, β = lateral inclination, γ = opening angle. The opening angle is a rotation about the D and K keys (Tittiranonda, Rempel, Armstrong, & Burastero, 1999)."

I might have to take my prototype split Katana out and try these values out...
« Last Edit: Tue, 25 December 2018, 01:18:17 by RominRonin »

Offline saint_james

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Re: Interesting scientific study - ideal slope, opening angle (tent), height
« Reply #5 on: Thu, 29 August 2019, 15:16:06 »
Did they determine an optimal range for β (lateral inclination) ?
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Online Findecanor

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Re: Interesting scientific study - ideal slope, opening angle (tent), height
« Reply #6 on: Thu, 29 August 2019, 15:59:34 »
The study in the OP does not compare different "tenting" angles. All tests are done with 14° (called "gable angle" in the paper)
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Offline saint_james

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Re: Interesting scientific study - ideal slope, opening angle (tent), height
« Reply #7 on: Thu, 29 August 2019, 17:39:47 »
Thanks Findecanor  :thumb:
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Online Findecanor

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Re: Interesting scientific study - ideal slope, opening angle (tent), height
« Reply #8 on: Thu, 29 August 2019, 18:12:34 »
The paper where that image is from does not do any tests itself, but quotes other papers mentioning tenting angles:
Kroemer et al (1972): 34° to 50°. The tested keyboard was columnar, so it mentioned true pronation.
Nakaseko et al (1981): 10°  Tested only 10° and 35°. Don't know if columnar or staggered.

Both papers miss the difference between columnar and staggered layouts: I think people tend to have have different pronation on left vs. right hand differently on staggered, and there are multiple styles.
Both papers also miss the relationships between opening angle, hand separation and staggering.
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Offline macroxue

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Re: Interesting scientific study - ideal slope, opening angle (tent), height
« Reply #9 on: Sat, 31 August 2019, 15:59:39 »
I don't believe there is one setup that can fit all. That's why we need flexible tenting with split halves. Besides the angles, the distance between the halves is also critical.

For me personally, I have these parameters.
Slope α = 0°,
Lateral inclination β = 30° ~ 45°
Opening angle γ = -10° ~ 0°
Distance δ = 20 cm between F and J.

In terms of providing comfort, I'd rate them β > δ > γ > α.
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Offline jacobolus

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Re: Interesting scientific study - ideal slope, opening angle (tent), height
« Reply #10 on: Mon, 09 September 2019, 15:14:48 »
I would not say they did this wrong, but that they hold one specific variable /table height/ as static (and varying other variables). Which is legit and normal methodological approach.

This is only a valid approach if all of the people tested are the same size.

The important feature determining the appropriate keyboard slope is the relative position of the torso and the keyboard surface. For different sizes of people, this will be different, even if the chair and table are held fixed.

It seems like in this study they set the height of the keyboard to always be either 4 or 8 cm above the height of the elbow, which is fairly reasonable (hopefully there’s not *too* much variation in the length of the subjects’ forearms).

The big problem with this study was that their “default” configuration A from which they made various other modifications was not very good, and left people’s arms in non-neutral positions with static muscle load. If they had started from a configuration where all of the joints were in neutral positions they could have seen how modifying it in any direction would make subjects trade-off various types of discomfort to compensate.

In their test condition where the keyboard is above the elbow, the keyboard should by default have a slight “positive” tilt, i.e. should be tilted up slightly at the back.  They also should have removed the palmrest, which caused all of their subjects to have slight wrist extension even in the negative tilt condition. (As compensation for the negative tilt, instead of flexing their wrists, their subjects lifted their elbows up and out to the side increasing forearm pronation and load on the shoulders.) If the palmrest is there, people tend to use it, because they think they are supposed to, even though it’s not as comfortable as ignoring the palmrest.

If they wanted to test the effect of a palmrest that should have been a separate experimental condition, and they should have picked a taller palmrest which didn’t require wrist extension to use.

It’s not clear why they set the seat backrest angle to 105° and told people to lean back. That’s not really a great long-term typing posture, IMO. I guess it’s better than what most office workers do in practice.

The best of the conditions (by empirical measures rather than subjective preference) they tested was E, with 0° tilt, height of 4 cm, and opening angle of 12°. When they increased the tilt (which subjects subjectively preferred), the subjects extended their wrists an uncomfortable amount, and also bent them outward (“ulnar deviation”). Some of their subjects liked configuration C, but that was because of the increased opening angle not the negative tilt.

They would have gotten a more comfortable configuration by adding some “tenting” to reduce forearm pronation, further increasing the opening angle to reduce ulnar deviation, moving the left half of the keyboard to the left (increasing distance between sides), picking a positive tilt of more like 4°, and dropping the palmrest.

It’s ridiculous that they only tested the 8cm height condition with a –8° negative tilt. When raising the keyboard higher it should be tilted up at the back, not down at the back.

A negative tilt is fine for a keyboard used on a low table (or for a standing desk) where the keyboard surface is slightly *below* the level of the elbows.
« Last Edit: Mon, 09 September 2019, 16:04:09 by jacobolus »

Offline jacobolus

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Re: Interesting scientific study - ideal slope, opening angle (tent), height
« Reply #11 on: Mon, 09 September 2019, 15:46:45 »
Besides the angles, the distance between the halves is also critical.

These can be traded off against each-other. The key layout matters too. If the goal is eliminating ulnar deviation, then you can either separate the two halves, change the “opening angle”, change the physical key layout, or change typing style. (Or for best results some combination of these.)

Having the two hands relatively close together is not such a big problem, but it does increase forearm pronation on a flat keyboard, which can be compensated for with “tenting” of two sides.
« Last Edit: Mon, 09 September 2019, 15:49:27 by jacobolus »