Ergonomic Armrests

To armrest or not to armrest? That is the question.

Here are the principles. The positions are critical.

Too high and your shoulders will be raised and therefore tensed. You will also have too much pressure on the forearms and the especially vulnerable ulnar nerve (funny "bone") at the elbow. Insufficiently cushioned armrests are particularly evil on the latter point.

Too low and you will be drawn into a leaning posture, collapsing the thoracic outlet in the neck and shoulders, putting undue pressure on the nerves and arteries feeding the arms, wrists, hands, etc. This also closes the rib cage around the lungs, reducing your capacity to draw precious oxygen that the blood needs to carry to your muscles for all of that continuous contracting (the same logic for the monitor being at eye level).

Too far apart and your shoulders will overwork (imperceptibly) because of the extension of the elbows, and your wrists will be deviated (bent on the horizontal plane toward the pinkies) when you type.

Too close and they may interfere with relaxed typing and with being able to place your hands in your lap (which you should do as often as possible, palms facing, to let the whole system relax).

Thin armrests actually require extra muscular effort to keep your arms on them.

I find with my clients that this is largely a matter of personal preference. With or without, know how to use or not use them.

And as always, make sure everything else is in place. Keyboard low enough (or chair high enough, with footrest only if needed), monitor in FRONT of you with the top roughly at eye level, don't reach as a habit, lighten up on keying and clicking pressure, stand up often, breathe, drink water, sleep, etc., etc., etc.

Gary Karp Onsight Technology Education Services San Francisco

ANSI Standards

Date: Fri, 10 Mar 1995 09:54:25 CST From: Nick Parker Subject: Re: station information

> From: Lynn Spagnesi > Are there a set of standards out there as to monitor height, keyboard > placement/height etc. that one follows? I can't imagine the commerical world > hasn't come up with some.

The only applicable US standards are ANSI/HFS 100, and MIL-STD 1472 (military).

ANSI/HFS 100 is *very* limited in scope. In the preface it states that it is applicable only to seated operation of textual displays. It does not cover color displays, large displays, non-keyboard input devices (mice, trackballs, tablets, etc), and it does not cover standing postures. It does not cover software or work practices.

Keep in mind that it is a standard, and *not* a practical guide on how to set up a work space. The main benefit of this standard is that it defines some common parameters, such as minimum leg clearance envelope, worksurface height, for a small (5th percentile) female, and a large (95th percentile) male. ANSI/HFS 100 was not a ground breaking standard, it simply formalized some existing information. If you'll check the anthropometric reference guides HUMANSCALE or MEASURE OF MAN, you'll see that ANSI/HFS 100 guidelines closely follow the data found in those (older) references.

ANSI/HFS 100 is in revision, and supposedly the new version is to be released this year. I receive updates from the ANSI/HFS 100 Canvass Committee, and my guess is that it'll be quite some time before we actually see it. It will be broader in scope, but don't expect any earth shattering developments.

OSHA was in the process of formulating ergonomics regulations, but it is highly unlikely (ice is likely to form you know where first) that they will be completed or released.

MIL-STD 1472 C is a general human factors reference for the military, and probably won't do you much good.

The primary EC (European Community) ergonomic standard is ISO 9241, which is a multi-part standard which covers many aspects of using video display terminals. It is much broader in scope than ANSI/HFS 100.

If you are trying to fit a workstation to a particular size person, or to a range of persons, the best place to look for *hard data* is in HUMANSCALE (MIT Press). Other sources of hard data are MEASURE OF MAN (Dreyfuss), HUMAN DIMENSION AND INTERIOR SPACE (Panero, Zelnik) and HUMAN FACTORS DESIGN HANDBOOK (Woodson). Due to its great bulk, the Woodson book also makes a fine boat anchor, speed bump, or battering ram! These types of books are typically used by designers, engineers, and human factors specialists.

Practical guides are probably the best type of reference for you. These typically are not original sources of hard data, like the volumes listed above. They are more day-to-day practical books intended to help the individual user or manager. Pascarelli and Quilter's book is often recommended on Sorehand. [I don't have mine here, and I don't remember the exact title.] CUMULATIVE TRAUMA DISORDERS (Putz-Anderson), and COMPUTERS AND VISUAL STRESS (Godnig, Hacunda) are useful. PEOPLE AND PRODUCTIVITY (Dainoff/Dainoff) has some related information, but I found it to be of limited use. THE ERGONOMICS PAYOFF (Lueder) is a good book. HUMAN FACTORS IN GEOGRAPHICAL INFORMATION SYSTEMS is targeted to users and managers of computerized mapping systems, but much of the information is applicable to any computer system. [Blatant plug alert! -- I have a chapter in that book.]

There are many small flyers and guides floating around. Some are good, and some are not. My physical therapist gave me a free flyer on how to properly set up a work space. It was written by the Joyce Institute, and it was very good.

> From: adam flint > Another simple rule to foolw when trying to set up your work station is > the 90 Degree Rule. You won't find this one in the books, but it is > what all of the ergonimic advice seems to lean to. It says that your > elbows, knees, hips, ankles, and any other joints that need to be bent > should be at 90 degrees, everything else should be straight- head, back, > wrist, etc.

The big thing missing from this recommendation, and from most of the published literature on the subject, is that it is a bad idea to hold this posture (or any other posture) for long periods of time. We need to move. Ideally, your furniture will allow you to work sitting or standing, be infinately adjustable between these extremes, and will allow you to transition between postures in a matter of seconds.

Nick Parker ( This e-mail address is being protected from spambots. You need JavaScript enabled to view it ) Mgr Design & Ergonomics Voice: 205-730-6208 Intergraph Corporation Fax: 205-730-6239 Huntsville, AL 35894-0001 Mail Stop: CR2901

Adverse Mechanical Tension - Reference

Date: Thu, 3 Mar 1994 22:11:03 -0800 From: Peter Bower Subject: Relavent AMT referances To: Multiple recipients of list C+HEALTH Comments: To: sorehand.

For those interested here are some of the referances to the AMT (now called neural tissue provocation testing) that I've found:

Devor M (1983) Nerve pathophysiology and mechanism of pain in causalgia. J Auton Nerv Syst 7:371-384

Ochoa JL, Torebjork E, Marchetti P, SWok M (1985) Mechanisms of neuropathic pain: cumulative observations, new experiments and further speculation. Adv Pain Res Ther 9: 431-450

Rasminsky M (1984) Ectopic impulse generation in pathological nerve fibres. In: Dyck PJ, Thomas PK, Lambert EH (eds) peripheral neuropathology, 2nd edn. WB Saunders, Philadelphia

Seltzer M, Devor M (1979) Ephaptic transmission in chronically damaged peripheral nerves. Neurology (Minneap) 29:1061-1064

Levine JD, Dardick SJ, Basbaum AI, Scipio E (1985) Reflex Neurogenic Inflammation. J of Neurosci Vol 5 No 5: 1380-1386

Elvey RL (1979) Brachial plexus tension tests and the pathoanatomical origin of arm pain. In: Glasgow EF, Twomey L, Aspects of manipulative therapy. Melborne. Lincoln Institute of Health Sciences. 1979: 105-110

Elvey RL (1986) Treatment of arm pain associated with abnormal brachial plexus tension. Aust Journ of Physio. 1986 : Vol 32. No 4.

Kenneally, Rubenach, Elvey (1988) The upper limb tension test - The S.L.R. of the arm. Grant R, (ed) Clinics in Physical Therapy. The cervical and thoracic spine. Churchill Livingstone: New York. 1988.

MacKinnon SE, (1992) Hand Clinic Vol 8 No 2 May 1992 (the first American M.D. to report the use of the Elvey Test clinically in the diagnosis of brachial and peripheral neuropathies.)

Quintner, (1989) Brit. J. of Rheum. 28: 528-533 (M.D. study of Elvey's Test in post MVA patients)

Peter Bower, M.D.

RSI and Adverse Mechanical Tension

Richard DonkinM

12 Feb 93

Version 2.0

I've received a few requests for info on Repetitive Strain Injury (RSI), including adverse mechanical tension (AMT), so I thought I'd put this note together.