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dmcfarlane
06-22-2005, 05:11 PM
Dear Colleagues,

Thanks for all the replies to my question “How hazardous is lifting after
prolonged sitting?”

Here is the digest report on the replies that many of you requested;

I recently received a query about the hazards of lifting after prolonged
sitting. I seem to remember being told that this is A BAD THING. If I
remember correctly this is something to with the slowness with which
muscles and tendons change length. However, I cannot find any records of
the evidence for this view or any details of how to deal with it. I
expect that there is evidence from truck drivers and their assistants
who have to load or unload after long periods of driving.

· Has anyone got any good refs I could consult?

· How long is too long to sit before doing strenuous lifting work?

· How long does the worker need to "limber up"?

· Do stretching exercises help at all?

Some of the opinions offered included;

· the key element (after prolonged sitting) is lack of warm-up

· 20 minutes is too long to sit before doing strenuous lifting work
(due to creep in ligaments)

· drivers who sit for 60 minutes or more are at increased risk of
back injuries

· muscles activation after prolonged sitting is better than stretching

Here are the details:-

Al Vangura Jr said;

Soft-tissue relaxation can contribute however the key element is lack of
warm-up.

Robert Schleip provided 3 references;

· Beach TAC, Parkinson RJ, Slothart JP, Callaghan JP 2005. Effects of
prolonged sitting on the passive flexion stiffness of the in vivo lumbar
spine. The Spine Journal 5(2).145-154. This suggests that spinal stiffness
increases in men (not women) after 1 hr of sitting, which e.g. results in a
decreased range of motion in forward bending.

· Solomonow M et al 2003 Journal of Electromyography and Kinesiology
13: 381-96. Shows that 20 min. of static or cyclic flexion results in creep
of lumbar connective tissues which does not fully recover over 7 hrs.

· Preuss R, Fung J 2005 Can acute low back pain result from segmental
spinal buckling during sub-maximal activities? A review of the current
literature. Manual Therapy 10:14-20 (here specially paragraph 5, in
relation to creep). Suggest that the chance of injury may be increased in
situations of increased creep (e.g. by prolonged sitting) due to resulting
decrease in the effectiveness of the neuromuscular reflex coordination.

Greg Hart mentioned that McGill (Stuart) has done work in this area. Here
are Greg’s responses;

· RE How long is too long to sit before doing strenuous lifting work?

He said that 20 minutes was his recollection (as a result of the creep in
ligament tissue that removes all or nearly all of the crimp. Ligaments have
more plastic than elastic character. The other factor is the "biasing" of
muscle spindle and tendon reflexes towards a less responsive arrangement.
All sitting is not created equal. The degree of slouch and the presence of
vibration or jarring would also impact the changes in the spinal
structures.

· RE How long does the worker need to "limber up"?’

The mileage will vary here and the most important feature of
the 'limbering' process will be countering the biases from sitting and
getting the muscles to 'think' extension again. Activities that emphasize
extension will be critical.

· RE Do stretching exercises help at all?;

Stretching - no, activation of muscles and 're-biasing' - yes


Tim Doyle said;

I saw a keynote by Stu McGill at the last ISB in Otago which discussed
similar matters. He spoke about research he did on NBA players sitting on
the bench for prolonged periods of time then going straight into a
game with little warm up. The problem was exacerbated in this population
due to the short height of the seats to allow spectators to see the game
over the heads of these very tall guys. I got this ref from his webpage,
a place to start at least; http://www.ahs.uwaterloo.ca/~mcgill/

REF; Green*, J., Grenier, S., and McGill, S.M. (2002) Low back stiffness is
altered with warmup and bench rest: Implications for athletes. Med. Sci.
Sports Exerc. 34(7):1076-1081.

Also selected and published in: Year Book
of Sports Medicine, (M. Alexander, editor), Mosby-Year Book Inc., St. Louis
2003.


Stephen Poon said;

After reading your question, I forward to my australian friend and he
replied me with the following answer. If you have any further question, you
can contact him directly because he is in Sydney.

His friend Sam Marigliano said;

Yes there is significant theories which support the idea that it is
dangerous to performing heavy or repetitive following prolonged sitting
particularly in a forward flexed or "hunched" position. This
will cause several problems:

· The inter-vertebral discs especially in the lumbar regions will be
compressed forcing shock absorbing fluid to leak out and become temporarily
desiccated. This will reduce the ability of the disc to distribute the
pressure of the load and may lead to annular rupture or failure upon heavy
lifting;

· The muscles and ligaments in the anterior abdominal region and
lumbo-pelvic region will be in a shortened position and creates a "forward
pull" on the lumbar-sacral region. This in effect causes a "tucked T'shirt"
effect whereby upon standing or lifting into and extended position the
tight muscles in the lower back have lengthen quickly which may lead to
micro-tears.

· From my experience with injured workers, there is strong evidence
to suggest that people such as truck drivers that sit for prolonged periods
(can be as short as 60min) are at increased risk of such injuries. I have
not viewed any quantitative research however I think the journals of Occ
health etc would provide some answers. I have
· prescribed basic lumbo-pelvic stretches and exercises to increase
the intra-abdominal pressure to many truck drivers which have helped to
reduce the risk of injury, these usually take ~2-3 mins to complete.

A later message from Al Vangura;

Great reference! Without having read the article yet - my first reaction
is that the static and dynamic postures that they placed the cats into
where beyond the cats' anatomical and physiological limits which caused the
injury. Or maybe pre-existing degenerative disease? I just ordered the
article and will comment after studying it.

The reply;

This might suit your interest (a mite technical though); "The recovery
period after flexion was characterized by ... an acute soft tissue
inflammation."

>From this abstract;

Solomonow M, Baratta RV, Zhou BH, Burger E, Zieske A, Gedalia A.:
J, "Muscular dysfunction elicited by creep of lumbar viscoelastic tissue,
Electromyogr Kinesiol. 2003 Aug;13(4):381-96.


Stuart McGill said that;

This can be either a long reply or a short reply. The short one would be to
see either of my textbooks - probably "Low back disorders" would be better
for this. No question the ligaments creep and "set" during prolonged
sitting.

Some people will develop stresses in their posterior anulus which takes
time to dispel after sitting to prepare for lifting. It would also depends
not only on the individual but time of day etc. Do they lift with a lot of
spine motion
or little spine motion as they bend more about the hips.

He also mentioned that ..”if sitting provokes back troubles then the issue
is heightened for that individual. For others it will be less important.”


Dr. Jack P. Callaghan said;

his research does examine seated work and > time-varying responses. He
said; I have attached a recent paper we performed looking at the changes
induced by sitting in the passive load carrying capability of the lumbar
spine. I also attached another paper on the flexion relaxation response of
the lumbar spine in sitting. As for recovery there isn't much on this as
you would need to look at a design similar to the time-varying paper and
then allow a standing recovery to see how the passive tissues recover.

One of the few studies I am aware of that has looked at anything relevant
to this was a paper by Stu McGill (McGill,S.M. and Brown,S. (1992) Creep
response of the lumbar spine to prolonged full flexion. Clin Biomech 7, 43-
46.) However, the results of this paper are not directly transferable to a
seated working position as the subjects held full flexion (ie arms hanging
down to their toes in a seated position), but it does give an indication of
recovery rate.

One of the posts (on ergoweb) in response to your query mentioned that the
lumbar spine is flexed to 60-80 degrees in sitting. Obviously this is
incorrect as the average RoM of the lumbar spine is about 60 degrees. They
should have indicated that some people adopt postures in prolonged sitting
up to 60-80 % of max flexion. This is from one of my papers (Callaghan &
McGill, 2001) that I have also attached.

Chuck Thigpen said;

I would suggest a warm up vs. stretching. There is no evidence that
stretching decreases the risk of injury. The detrimental effects may
include mechanisms as: alterations in the spindles and GTO's due tension
and change in length during stretching, may change the length of the muscle
but there is evidence that the strength decreases immediately after
stretching.....That said, I do believe stretching seems better than nothing
but, I would suggest encouraging the individuals to get up and walk fast/up
stairs etc...to get their heart rate up then maybe some dynamic movements
to get the body going. For example; squatting, jumping jacks, lunges, maybe
even "shadow lifting" where they imitate the lift they will be doing. Hope
this is helpful.

Laurel Kincl said that;

Stuart McGill has a good reference book for low back injury prevention. He
is at University of Waterloo and may be able to speak more on this.
According to him and other resources, I think that disc health is the
problem. Sitting requires flexion of the low back unless you have proper
lumbar support. Flexion will cause the disc to "shift" in the posterior
direction. This does not immediately correct after the spine returns to
neutral (standing up after sitting) as the spine has a memory.

Extending the back can help cause negative pressure that will assist the
nucleus to neutral position. Low back stiffness is altered with warm-up
and bench rest (Green et al, 2002)

Green*, J., Grenier, S., and McGill, S.M. (2002) Low back stiffness is
altered with warmup and bench rest: Implications for athletes. Med. Sci.
Sports Exerc. 34(7):1076-1081.

Also selected and published in: Year Book of Sports Medicine, (M.
Alexander, editor), Mosby-Year Book Inc., St. Louis 2003. See;
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?
cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12131244

Postscript

I found the following advice in the textbook by Stuart McGill;

· Increasing the strength of back muscles does not reduce the risk of
back injury but increasing their endurance does. Exercises designed to
enhance athletic performance are usually detrimental for back problems (p
12)

· The recuperation needed after prolonged sitting before lifting
tasks takes a long time; it takes 30 minutes or more after extreme flexion
of the back though about fifty percent is achieved within the first two
minutes (p 171)

· When a worker has to sit for prolonged periods provide lumbar
support to keep the worker’s back flexed. The worker should try to sit
upright position rather than a slumped one (p 181).

Reference

S. McGill, (2002), "Low back disorders. Evidence-based Prevention and
Rehabilitation", (Human Kinetics, Leeds) pages 119, 123 and 124.


Regards,

David McFarlane
Ergonomist,
WorkCover Authority of New South Wales

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