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The Nottingham chair for sit/stand office work

Preventing back injuries

by Dr. E.N. Corlett

 

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Osmond sells the Checkmate in the UK.

Preventing back injuries from sitting at work

E.N. Corlett, Phd

The act of sitting down is so simple that we don’t think about it very much.  After all, we just bend our knees and there we are, sitting.  Taking the weight off our legs is also an immediately comfortable feeling, so almost any seat feels comfortable in the short term.

But if you work at a job that requires extended periods of sitting, for instance at a computer, then in the longer term “almost any seat” can do serious damage.  A recognition that this is so has given rise to several reports on back pain in school children,  A recent publication by BackCare, (2005), reported that one in five secondary school pupils experienced back pain, of which 23% visited a medical practitioner, results similar to the adult population.  Their report draws attention to the important role of the chair and desk combination as a major item for improvement and gives recommendations for better furniture.

Studies of seated work in industry and commerce has produced many recommendations for improvements in the layout of workplaces, whilst research has revealed the reasons for such problems as upper limb disorders.  However, although there is much research into the effects of sitting, in most of the workplace recommendations this research fails to influence recommendations on the choice of seat.  Whilst there is emphasis on lumbar support, seat padding and a curved front edge, the basic problem discussed by Mandal, (1974) and repeated by him and others many times since, is not addressed.

This problem, which has been studied in detail by many researchers in the last thirty years, concerns the shape of the spine when sitting.  The (lumbar) curve, present in the lower back when standing, allows the transfer of the weight of the upper body to the legs through the spinal discs with the least deformation of these discs.   The effect of sitting on a horizontal seat is that the pelvis is rotated backwards, which flattens the lumbar curve, deforming the discs and adding extra pressure to them as a result.  The flattened curve also causes tension in the back muscles to maintain the sitter upright, loading the discs still more.  These continuous extra loads reduce the available capacity of the discs to transmit external work loads.

These adverse effects can be avoided, and the lumbar curve substantially retained, if the seat is sloped to allow the thighs to remain at about 20 degrees below the horizontal.  A sloping seat will not remain comfortable for long because the gravity load will tend to cause the sitter to move down its surface, displacing lower garments upwards and adding extra load to the legs to hold the sitter on the seat.  But if the seat is curved from front to back, sitters can sit on a horizontal surface at the top of the curve whilst their legs remain at the desired slope.  Furthermore, if, when the chair is adjusted for height, the seat is arranged to tilt, the seat angle will be altered but the sitters still sit on a horizontal segment at the top of the curve, whilst their feet can remain on the floor.

Seats to this design are available and have been used in offices, checkouts, factories and elsewhere.  Research evidence shows that the spinal discs are under much less loading with this design than when compared to a conventional horizontal seat.  These results support the contention of earlier researchers and show that this design is more favourable for retaining a healthy spine than the use of conventional seating.  The risk of spinal damage is reduced whilst the chances of keeping a healthy back are much increased.

 

BackCare   (2005)  Back pain in children and young people.  Publ. by BackCare. Elmtree Road, Teddington, TW11 8ST, UK

Mandal, A C  (1974)  The seated man, (Homo Sedens)  (3rd.Edition 1985) Dafnia Publications, 2930, Klampenborg, Denmark

 

Nottingham features  |  Patents  |  Lumbar spine seating

Slideshow: Nottingham sit-stand chairs by E Nigel Corlett  |  Cites  |  Key points (pdf)

Sitting and seating  |  Stadiometers and cites  |  Dr. Corlett's paintings  |  Humor

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