Anything to help a PC Reflex support person :-)

I am unfamiliar with any general rule for determining a safe lifting weight as a percentage of body weight.

Part of the problem is deciding what is safe as it is may depend on number of lifts, and what type of injury you want to avoid.
You may want to look at some of the work done by Stover Snook. He has considerable data describing the "Maximum Acceptable Weight of Lift (MAWL) " for a population (using a modified psychophysical approach). I suppose you may be able to find data on the average weight of the tested sample, and determine a percentage of Body weight to make your calculation. Be careful, though, there is considerable debate as to if a MAWL is really "safe". Snook's work has been carried out to describe several different populations under different lifting conditions (names that come to mind are Ann Mital and Waldemar Karwowski - Just look in the Human Factors Journal). In grad school, we wrote a paper (Human Factors, mid 90's, Davis et. al.) describing how some of the differences in MAWLS were attenuated when the moment arm of the external weight was included.

There are also several published biomechanical models that you could explore. The easiest would probably be along the lines of Don Chaffin's static, lumped muscle models. To do this you will need to work with moments instead of just weights and make some assumptions as to what is a "safe" spine load. Such an analysis, however, should be easy enough for a PC reflex setup.

You may also want to look at the NIOSH lifting equation, Waters et al. Ergonomics, 1993.

IMHO, if you want to get the best estimate of safe lifting, look at Marras et. al. Ergonomics 1995.

Some keywords to try when searching: Manual Materials Handling, Lifting, Musculo Skeletal, Biomechanics, Biomechanical limits, psychophysics, maximum acceptable weight of lift (or MAWL)

Bryan Kirking
Research Engineer
Department of Orthopedic Surgery
Baylor College of Medicine
Houston, Texas

-----Original Message-----
From: Andrew Mahar [SMTP:andrew@QUALISYS.COM]
Sent: Friday, July 24, 1998 11:33 AM
Subject: percent lifting of BM

Hello all,

I have a question or two regarding the strength to weight ratio
considerations for different populations. I have reviewed the archives
searching for parameters set for SAFE, effective lifting percentages per
body mass, but have not found a straight forward answer (if there is
one). I admit that I am unfamiliar with this particular area of study
and couldn't immediately pull journal publications.

I am ignoring the age group 1-20 for both males and females so that
puberty and the effects of growth changes to bone and muscle tissue have
reached completion. NOTE: I do agree that there are still adaptive
changes due to beginning/stopping exercise and other factors.

The lifts I am only concerned with at this point are lateral
flexion/extension of the trunk and anterior flexion of the trunk with
the feet placed shoulder width apart and symmetrically oriented along
the AP direction.

(1) Does research/practical experience state that a "light" lift is
considered to be 10% of BM and a "heavy" lift to be 25% of BM for any
individual irrespective of height, weight and height-to-weight ratio??

(2) Are these percentages too low, too high, or are they effective for
testing both a 35 year old male and a 70 year old female (thus, an age
independent measure)??

I realize that age has a high correlation with absolute lifting strength
and I am trying to determine conditions which will prevent injury, while
allowing me to make comparisons of people in different age groups based
on a lift of a mass relative to some percent of BM.

The usual reply/posting SOPs apply here. Thanks for your help.


__________________________________________________ ________
Andrew T. Mahar
Research Biomechanist

Qualisys, Inc.
148 Eastern Blvd., Ste. 110, Glastonbury, CT 06033
Tel: 860-657-3585 Fax: 860-657-3595
__________________________________________________ ________

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