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ERGONOMICS  January 2010

ERGONOMICS January 2010

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Subject:

Sitting and Lifting

From:

David McFarlane <[log in to unmask]>

Reply-To:

David McFarlane <[log in to unmask]>

Date:

Fri, 29 Jan 2010 02:59:45 +0000

Content-Type:

text/plain

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Parts/Attachments

text/plain (116 lines)

Dear All,

Does anyone know of a government guidance publication that attempts to 
deter designers from designing checkout workstations for seated workers (or 
any other seated workstations for workers who have to do lifting tasks for 
that matter)? We used to have one or two in Australia but I seem unable to 
find them now. Failing that is there one discourages drivers from performing 
lifting tasks immediately after prolonged sitting?

According to my records the arguments for these recommendations are as 
follows. The hazards of lifting during or after prolonged sitting have been 
researched in Ergonomics at least as far back as the seventies; that era 
featured some landmark papers that contended that tasks involving prolonged 
sitting (sitting for a period of 4 hours or more) can lead to lower back pain 
(Magora, 1972). 

This is a particularly severe problem for drivers.  Workers who spend more 
than half there working life driving all three times more likely to suffer from 
back trouble than the rest of the population (Troup, 1978). Alteration of 
postures between sitting and standing appears to reduce the risk of back pain 
and back injury (Magora, 1972); periodic alterations of seated postures are 
also beneficial since the discs do not have a blood supply and intermittent 
movement is necessary for their nutrition. 

The “Eleven Commandments of Ergonomics” stated that work procedures 
should be designed to ensure that the worker does not have to stand 
continuously for more than 30 minutes or sit continuously for more than an 
hour (Van Wely, 1970) wherever this is possible.

The topic of lifting during or after prolonged sitting has been researched with 
even greater rigor in recent years. Canadian research in the field of sports 
physiology has found that bench rest after a warm-up leads to an increase in 
the stiffness of the lumbar spine prevents optimal performance and increases 
the risk of back injury (Green et al, 2002). 

Research shows that sustained static loading of lumbar visco-elastic tissues 
can cause micro-damage to its collagen and this can cause muscle spasms 
and results in inflammation (Solomonow et al, 2003). A mere 20 minutes of 
static flexion results in creep of lumbar connective tissues that does not fully 
recover over a 7-hour period.

Current evidence from the field of Manual Therapy suggests that prolonged 
sitting increases the chance of injury because increased creep and the 
resulting decrease in the effectiveness of the neuromuscular reflex 
coordination (Preuss and Fung, 2005). It is now believed that prolonged sitting 
may increase the risk of low back injury due to changes in the passive flexion 
stiffness of the lumbar spine (Beach et al, 2005).

Professor Stuart McGill provided the following advice in the textbook on low 
back disorders:

·	  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; hence the worker should sit in an 
upright position rather than a slumped one (p 181).

In summary a worker needs at least two minutes of recuperation (standing or 
walking) after prolonged sitting and preferably 30 minutes. Workers who have 
to do lifting task should be encouraged to sit in an upright position rather than 
a slumped position.

Has anyone else published anything recently that I could quote? Has any 
organization with authority and influence published anything that is apropos?

Regards,

David McFarlane MAppSc (Ergonomics)
Ergonomist, WorkCover NSW

Disclaimer

The views expressed above are those of the author and they do not 
necessarily reflect the views or policies of WorkCover NSW. Any 
recommendation concerning the use or representation of a particular brand of 
product in this document or any mention of them whatsoever (whether this 
appears in the text, illustrations, photographs or in any other form) is not to 
be taken to imply that WorkCover NSW approves or endorses the product or 
the brand.

References

1. A Magora, (1972), " Investigation of the Relation Between Low Back Pain 
and Occupation", Industrial Medicine, Volume 41, no. 12, December 1972.

 2. D Troup, (1978), " Drivers back pain and its prevention ", Applied 
Ergonomics, 9.4, pp 207 - 214.

3. P. Van Wely, (1970), "Design and disease", Applied Ergonomics, 1.5, pages 
262 - 269.

4. Green J, Grenier, S and McGill, SM, (2002),  “Low-back stiffness is altered 
with warm-up and bench rest: implications for athletes”, Med Sci Sports 
Exerc, 2002 Jul, 34, (7), pp 1076-81. See 
http://www.ncbi.nlm.nih.gov/pubmed/12131244

5. Solomonow M, Baratta RV, Zhou BH, Burger E, Zieske A, Gedalia A, 
(2003), “Muscular dysfunction elicited by creep of lumbar viscoelastic tissue”, 
J Electromyogr Kinesiol, 2003 Aug, 13, (4), pp 381-96. See 
http://linkinghub.elsevier.com/retrieve/pii/S1050641103000452

6. 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”, Man Ther, 2005 Feb, 10, (1), pp 14-20, paragraph 5. See 
http://www.ncbi.nlm.nih.gov/pubmed/15681264

7. Beach TA, Parkinson RJ, Stothart JP, Callaghan JP, (2005), “Effects of 
prolonged sitting on the passive flexion stiffness of the in vivo lumbar spine”, 
Spine J, 2005 Mar-Apr, 5, (2), pp 145-54. See 
http://www.ncbi.nlm.nih.gov/pubmed/15749614

8. S. McGill, (2002), "Low back disorders. Evidence-based Prevention and 
Rehabilitation", (Human Kinetics, Leeds), pages 171-181.

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