Answer to Question 6
This website is being
totally rearranged in the autumn of 2011 to concentrate on the one central
point described on the website front page.
On that page there is a list
of questions and the answers are on these linked pages. These answers may be
complete, preliminary or not yet done. Hopefully most will be done by lat
October 2011.
The answer is civilised forms of sitting,
particularly sitting with a backrest and particularly when driving. A backrest may limit the total flexion of the
spine but the effect is always to increase the flexion of the lowest spinal
joints (L 4-5 and L 5-S.) in comparison with unsupported sitting. This effect was shown in the tabulations in
the paper “The influence of backrest
inclination and lumbar support on lumbar lordosis” (1) in Spine
1979 (though not observed by the authors)
The significance of this for back pain is
difficult to detect statistically as it is so universal. However the effect of car driving was noted
as early as 1972 by Kelsey and Hardy (2), was confirmed in 1986 in Spine (3)
and was strongly emphasised by the work of Professor Mark Porter, Professor of
Ergonomics at Loughborough University who observed "-- -- a sixfold
increase in -- -- low back trouble by car drivers who spend more than half the
working day behind the wheel"(4)
Would we expect this
mechanically? The answer is definitely
yes. Car seats tip the thighs and
therefore the pelvis further back than almost any other seat. Car seats incorporate far more direct
support for the lumbar spine than any other seats. We sit still in a car seat
for far longer than we ever sit anywhere else. This mechanical situation could
not be better designed to cause the problem outlined above.
For a mechanical analysis of all forms of sitting
see the booklet "The Evolution of Low Back Pain" by John Gorman which
is a free download on this website. (5)
(1) Anderson GBJ, Murphy
RW, Ortengren R, Nachemson AL The influence of backrest inclination and lumbar
support on lumbar lordosis. Spine 4: 52-58, 1979
(2) Kelsey JL, Hardy AJ
Driving of motor vehicles as a risk factor for acute herniated lumbar
inter-vertebral disc. Amer J Epidemiol 102: 63-73, 1975
(3) Biering-Sorensen F,
Thompsen, C Medical, social and occupational history as risk indicators for
low-back trouble in a general population.Spine 11: 720-725, 1986
(4) Seating Design.
Current Problems and Future Strategies Dr J. Mark Porter. Automotive
Interiors International. Pages 6 to 19.
199?
(5) The Evolution of Low
Back Pain.