PDA

View Full Version : SUMMARY OF RESPONSES: Anthropometric scalability question -Push/Pull Forces



Matt Kuklis
08-03-2004, 05:26 AM
BIOMCH-L folks,

Thanks so much for those of you who provided input with respect to my
question regarding scaling population percentiles. Most of the
respondents had some disclaimer related to not directly being able to
accurately scale population data as well as if one does scale he/she must
understand the results as to not misuse them. It is certainly my
understanding that when dealing with ergonomic data, it is always best to
err on the side of conservative. Thanks again for the feedback!

Please see below for the original question and a summary of responses.

Matt Kuklis
Biomechanical Engineer
Hill-Rom Co., Inc.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Original Email (Question):

Group,

A colleague and I are working on a project to try to understand a
comfortable range of push/pull forces that a 5th percentile female can
endure. We have found many tables of forces published by many individuals
mostly to do with maximum endurance forces for various push/pull
exercises. We found a decent representation of our application in
Dreyfuss' "Measure of Man and Woman". However, the forces given are for a
50th percentile male. Dreyfuss gives a male to female scaling factor of
2/3; we've also seen scaling factors around 1/2. We are interested in the
5th percentile female as I have mentioned.

Is there any such scaling factor/conversion that can take data (in
particular push/pull forces) from one segment of the population (based on
percentile) to another (e.g., is there a conversion to take data from 50th
percentile to 5th percentile)?

Short of doing our own study, is there a better way to get the data more
directly? For instance, is there a more gold-type standard/study of
push/pull forces for various exercises (i.e., forearm/shoulder in
different orientations; sitting versus standing, etc.)?

A summary of responses will be posted. Please indicate if you would like
your name removed from the summary posting.

Thank you for any information.

Matt Kuklis
Biomechanical Engineer
Hill-Rom Co., Inc

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


Hi Matt:
I am not sure what data you have access to, but if the Dreyfuss data are
true percentile data then they can be represented by a normal distribution curve. The 50th percentile will correspond to a Z-score of 0.0. Using this distribution,
you can find the Z-score that corresponds to the 5th percentile female by looking up a conversion in a Standard Normal Probability table (see for example, http://www.math2.org/math/stat/distributions/z-dist.htm, http://psych.colorado.edu/~mcclella/java/normal/normz.html, http://davidmlane.com/hyperstat/z_table.html).
Using this conversion, you will see that the 5th percentile on a normal curve corresponds to a Z-score of about -1.6452. If you have the standard deviation of the measures used by
Dreyfuss, you can then calculate the actual mean values for a 5th percentile female by solving:
Z = (Y-MEAN)/SD
where Z = the z-score (-1.6452); Y = the 5th percentile female value (to be solved); MEAN = the population mean (the Dreyfuss female 50th percentile/mean force); and SD is the female
population standard deviation.
I hope that works. I don't know another way to do it. Let me know how it comes out.
Peter
______________________________________
Peter F. Vint, Ph.D.
Research Scientist

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Matt,
You need to look at the Snook Liberty Mutual Psychophysical Tables.
Carter Kerk

Carter J. Kerk, PhD, PE, CSP, CPE

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Hi Matt

Muscle forces are generally proportional to muscle cross-sectional area,
so to approximately (body mass)^2/3. You could use that to convert data
from male subjects to females, if you knew the body mass of both groups.
However, although that would account for the effects of size, it
wouldn't allow for any sex differences.

I don't think you can convert from the 50th percentile to the 5th
percentile without knowing what distribution the data follow and having
a measure of their variability.

Hope that's some help. Good luck with your work,

Sharon

------

Sharon R. Bullimore

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

These articles do evaluate push/ pull.

Much of Snook's work uses psychophysical information. The articles
probably will
not give you conversions that allow adjusting data from the 50th
percentile male to accommodate the 5th percentile female. The 1990
article in ergonomics does consider females as well as males.


Ciriello VM. Snook SH. Hughes GJ. Further studies of psychophysically
determined maximum acceptable weights and forces. [Journal Article] Human
Factors. 35(1):175-86, 1993 Mar.

Snook SH. Ciriello VM. The design of manual handling tasks: revised
tables of maximum acceptable weights and forces. [Journal Article]
Ergonomics. 34(9):1197-213, 1991 Sep.

Ciriello VM. Snook SH. Blick AC. Wilkinson PL. The effects of task
duration on psychophysically-determined maximum acceptable weights and
forces. [Journal Article] Ergonomics. 33(2):187-200, 1990 Feb.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

There are no valid scaling methods available to transform a 50th
percentile
person to a 5th percentile person. The reason for this is that the concept
of a "5th percentile person" is neither biologically nor statistically
valid.

Thomas M. Greiner, Ph.D.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Hello Matt,

I would agree with the previous speaker about converting data. Better to
obtain a better data source. I have here on my bookshelves a book called
"Adultdata", published by the Dept of Trade and Industry in the UK. It has
a
whole raft of tables related to different pushing/pulling situations, and
gives 5% and 50% values for males and females.

I think you can get a free copy if you send them a mail.

Good luck,

Jan Herman Kuiper

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Matt

You talk about "enduring" forces. Do you meant that the force is being
applied to the person and they have tor resist it or do you mean that they
have to exert that force for a set period of time?

I'm surprised you don't seem to have found Snook's psychophysical data
which includes maximum acceptable pushing and pulling forces for males and
females. He quotes values down to 10th percentile so you will need to
calculate the SD from his figures to calculate 5th percentile.

Also, I've not seen a copy of Dreyfuss lately but that data is now very
old, and probably originally from the US military so will be biased
towards
young fit males

The suggested female:male strength ratio of 2:3 is almost meaningless.
Steve Pheasant pointed out in 1983 that there is actually tremendous
variability in it.

You might also find the U Michigan "3D Static Strength Prediction Program"
of use - it can predict the percentage of the population capable of
exerting a given force in a given direction in a given posture. Sorry,
but
I don't have the URL to hand but a search of the umich.edu website should
find it/

Some suggested references:

Snook SH and Ciriello V (1991) "The design of manual handling tasks:
Revised tables of maximum acceptable weights and forces". Ergonomics 34,
1197-1213
Pheasant ST (1983) "Sex differences in strength - some observations on
their variability" Applied Ergonomics 14, 205-211
A recent report by a couple of my colleagues: RR228 - Review of the risks
associated with pushing and pulling heavy loads
http://www.hse.gov.uk/research/rrhtm/rr228.htm



Regards

Andrew

Dr Andrew Pinder, PhD, MSc, Eur Erg, MErgS

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Hi Matt,

The Health and Safety Executive in the UK has just recently done a review
of the risks associated with pushing and pulling. Quite a bit of
information on pushing / pulling forces is brought together, and you find
it helpful in directing you to other sources. It is Research Report
RR228,
"Review of risks associated with pushing and pulling heavy loads", which
can be downloaded free from the internet (
http://www.hse.gov.uk/research/rrhtm/201-300.htm ) or purchased from 'HSE
Books'.

Alternatively, the Department of Trade and Industry in the UK have
produced
two free books called "Strength Data for Design and Safety": Phase 1 and
Phase 2. (obtained through www.dti.gov.uk I believe or by calling +44 20
7215 0383). It presents data according to age for a range of pushing and
pulling tests, which may be of help.

Good luck,

Jeremy Ferreira

-----------------------------------------------------------------
To unsubscribe send SIGNOFF BIOMCH-L to LISTSERV@nic.surfnet.nl
For information and archives: http://isb.ri.ccf.org/biomch-l
Please consider posting your message to the Biomch-L Web-based
Discussion Forum: http://movement-analysis.com/biomch_l
-----------------------------------------------------------------