Category Archives: DIGRESSIONS

Includes, A look at the way people actually sit. Various chairs and how they measure up.


Evidence, for design, based on the perception of comfort, is biomechanically worthless.   Conversely a chair that has correct biomechanics is always comfortable.   Correct Biomechanics = Maximum Comfort.       Discomfort is probably a different modality and is significant.

Screen Shot 2018-09-23 at 12.08.55It is very understandable that the chair industry regards comfort as it’s ultimate aim. That is what the users want and that is what pays.  Discomfort indicates that something is wrong.. However design based on a search for maximising ‘comfort’ can be misleading.  It is a treacherous guide  which only turns up truthfully when the bio-mechanics (ergonomics) are fully correct.  The correct answer should be the Hippocratic ‘Do no harm'”

This can only be effected from medico-scientific design.   Observation confirms  the working assumption that an optimised configuration would inevitably ensure maximum comfort.

The Public judges a chair by it’s immediate comfort and intelligently ignores the ergonomic benefits described by the salesman.   I am told that this is not so in China where the health benefits are paramount.Screen Shot 2018-06-11 at 21.01.07


I had rather forgotten about ‘comfort’ as it had been shot down by the scientific community as far back as 2003.  When  I asked several top chair designers at a trade show (2015) all gave  ‘comfort’ as their main objective.    They failed to understand that comfort, free from adverse effects, can only be achieved by an understanding of spinal biomechanics and necessary requirements incorporated into the design. Such a design is, by it’s nature, always comfortable.

This misunderstanding seems to have misled the industry up a wrong path which has resulted in the absence of any chair in the market that is not likely to exacerbate LBP on prolonged use.  Much of the ‘ergonomic’ research on  seating seems, to be based on the ‘comfort’ assumption. For example, “Trial 1. A test chair was created with 35 spring-loaded diodes to measure support in the lower back region by remote control. 200 test persons have adjusted the support in he lower back region again and again until they felt comfortable. The sensors provided the scientists with data which they evaluated using pressure mapping technology. The procedure was repeated several times and the results were clearly confirmed”.   This, based on biomechanically worthless evidence gives no help in assessing what is correct for the underlying spinal constituents.  Even today (2016) a Hermann Miller article writes as it’s 1st principle for design   “1. A chair should be perceived as comfortable before, during, and after sitting upon it. Comfort is as much a matter of the mind as of the body.”.   Perceived by the mind is perhaps OK, but is no substitute for the body (spine) which requires correct biomechanics.

Gorman, who developed the concept of ‘Iliac’ support and has been involved in car seat design, wrote to me   “Comfort tells you nothing” and continues “The car industry has to concentrate on comfort because we spend so much time sitting still in cars. They measure comfort as a lack of localised pressure and have lots of methods to measure it. This used to be large mats of little bubbles which could be individually measured for pressure. Now there are probably much better with mats of pressure sensitive material like large touch screens.  This was always a problem for me when I got my prototypes evaluated by Fiat, Magna, Chrysler, etc. My pelvic support does require force round the iliac crest so even if the seat was subjectively comfortable it would fall down on the pressure measurements”.

Rani Lueder wrote (19/8/12)

“On your comment about comfort, this link to my web pages discusses the origin or this, and the reason that no one really asks about comfort anymore, discomfort is pretty standard. Namely the Corlett and Bishop article (1976) completely turned our head on the issue. They pointed out that not only is comfort nearly impossible to measure in a predictable way, but it is not the opposite of discomfort – and may even be an entirely different dimension” .

Anecdotally, I have seen many chairs pronounced as marvelously comfortable and ergonomically ‘correct’, which have biomechanics faults.  I was asked to see a control room which was responsible for the UK nationwide supply of a major utility. The control room had been optimised for it’s indoor environment so that the air quality, lighting, sound abatement, humidity and colour scheme were marvelous. Everyone was happier, and absenteeism and minor morbidity had decreased. The exception was that backache had remained constant. I found that the workforce, had been allowed to choose the chair. Of course, the most wonderful, expensive, all singing, all dancing chair had been chosen. The staff gave it full marks in the questionnaire. The only trouble was that it gave inadequate support to the lumbar spine.

A chair designed along 2T (3M) principles was judged “This chair is much too comfortable. My work force will go to sleep”. This was the comment of a CEO  who was lying on the prototype P1.  Seat and backrest were of roughly, but correctly, moulded plywood with no padding whatsoever.  This was a common reaction of management.   A 2M (2T, BiModal) or 3M design (TriModal) is based entirely on bio-mechanical research and, pro tem, can be used for comparison to assess the effectiveness of any chair design.

 The 2T is the default  against which the ergonomics of any chair can be assessed.    An essential tool for chair designers. It is optimally comfortable.  2T CONCEPT a full solution

A converse approach.

The comfort of the 2T concept was constantly remarked regardless of the nature of back & seat components.   This, to some extent,confirmed the working assumption that an optimised configuration would inevitably ensure maximum comfort.  The scientific evidence shows optimised configuration can only occur in a reclined mode.

The ergonomic research approaching from the opposite direction and largely financed by industry, was suspect.   This is changing.  A recent overview editorial by P. Vink in Applied Ergonomics  has evaluated a number of comfort/discomfort models and has proposed a new one.  This draws heavily from the work of Moes, N.C.C.M., 2005 and De Looze,2003.

Although the work of Kee and Lee is described which stresses physical loading and posture holding time,  torque at joints, and compressive force at L5/S1, a number of less bio-mechanic related factors are included.  These include the physical environment + task, psychosocial factors, internal human body effects  and aesthetic design.  Although interesting these are hardly relevant to chair design.                                                 HAS

Next. The 2T chair is intended for office use and office environment in general.  See ☛ 2T in the office→

☛ Exercise & movement

Next ☛SLEEP →



School chairs & desks

A quick look through retailers of school chairs and desks failed to find any models that had the slightest regard for ergonomics.  Astonishing!   Especially as this may be where adult LBP begins.

School chairs

This post is not intended to be authorative on children’s and school seating.  In view of the importance of the subject a few points arise from the spinal biomechanics .

It would seem that non-western populations that do not habitually sit in upright chairs have a low, or no, incidence of LBP and are able to squat and sit slumped.  It has been shown that they have a larger sacral-horizontal angle  and a larger lumbo-sacral (L5/S1) angle which, safely, does not reduce below 0° on flexion (see. ‘Angles & lordosis).  This may partially represent a racial genetic advantage but cannot be the whole story as the same people incur the same incidence levels of LBP when the upright sitting posture is adopted in childhood.   This suggests that adverse mid- upright sitting postures in childhood modifies the spinal bio-mechanics and so may determine future liability to LBP.   Early stretching of the posterior elements of the motion segment which, in turn allows spinal joint instability and early disc degeneration (see CTD ) is likely.   It may even be the fundamental cause.  More research is required.

On this assumption, school chairs or chair/desk combinations should be properly designed to ensure, as far as is possible, bio-mechanical optimisation.  This can be done at no great cost using a FTS tilting seat and a back rest with Iliac support in a height adjustable desk/chair unit.   In theory, at least, this would avoid the stretching of the posterior stabilising ligaments.   Some positional instability allows  movement   which aids the pumping action of position changes for the  nutrition of the IV disc, also a factor helping to avoid later degenerative changes.

There are some general childhood requirements:-

  • Sturdiness so as to withstand a childs natural curiosity to test to destruction.
  • Allow freedom of movement for small children with short attention spans.
  • Absence of any holes and crannies into which fingers or other objects can be stuck.

School and schoolroom requirements

  •  Cost considerations
  • Stackability.

The essential bio-mechanical requirements for school chairs are the same as for an adult:-

  •  A forward tilted seat
  • or/and Iliac support.
  •  Height adjustability of desk & chair.
  • Avoidance of, commonly advised, incorrect systems.
  •  A 2T chair is hardly practical in a school environment, but not at home.
  • The requirements for a school chair/desk may be different from those of a small child. Small children seem to enjoy and do well on a large ball. This ensures a FTS, freedom of movement and seems to be safe.

Screen Shot 2013-09-27 at 22.38.45My ‘off the cuff’ idea of a design for a school chair and desk combination. →

Note that these measurements are considerably greater than the ISO recommendations – it is difficult to understand on what the latter measurements were based.

Screen Shot 2015-09-30 at 15.04.45


←I was amazed to see something almost identical on eBay although possibly intended for adults and not much ‘Adjustment’.  I tend to decry adjustment for adult seating  See → Adjustments . 

KnollAnother chair by Knoll for adults seems relevant.



An existing good start, for consideration, is a model  from the German firm MOLL.  The design  suggests that it still subscribes to the outworn ‘correct’ upright sitting concept.  This may be a necessary constraint.

  • Screen Shot 2013-10-22 at 18.05.04 Screen Shot 2013-10-22 at 18.05.52⟵ The ‘Scooter’ is the simplest and, possibly, best.
  • Adjusts easily to the growing size of the child.
  • Allows movement.  Absence of arm-rests may help here.
  • A FTS to allow the hip angle to be “slightly open (more than 90°)”.  Ideally should be greater, to 130°.
  • Some degree of pelvic support. Could be improved.

A quick look through retailers of school chairs and desks failed to find any models that had the slightest regard for ergonomics.  Astonishing!

The FIRA publication is worth looking at in this respect   “We as a nation are embarking upon a major investment in our schools and teaching methods – but our school furniture design has changed little from the post-war era. It’s not just about aesthetics ….This call to action comes from FIRA (Furniture Industry Research Association) in response to requests from government, purchasers, parents, teachers and children to make a change”.

They adhere to British Standards BSEN 9241 Pt 5.

FIRA2014-04-03 at 14.26.56The bio-mechanics of the charming looking chair pictured on the front page seems to be as adverse as it gets.  It is not clear if this is being recommended or dis-recommended.  Can you spot the faults?


See chair remediation→


From Rani Lueder
There is a large amount of evidence that children – particularly as they approach puberty – are prone to back pain, that these symptoms can be medically established, and that their rate of pain compare with those of adults. Not that their symptoms mean the same thing as they do in adults, mind you, but they’re comparable. And children and adolescents who have symptoms are particularly prone to exhibit evidence of back symptoms later in life – that is, a decade or so later. My book is beginning to look dated at this point (there’s so much research) but unfortunately I can’t point you to a more up to date resource, it’s still the most thorough review.

Thank you, Rani
Very helpful. I must admit to being shocked when I looked at the children’s chairs being retailed, at least in the UK.
Dr Henry Sanford


Various chairs. How do they measure up?

Ergonomics of sitting safely.   My remarks are intended only to illustrate points in relation to the 2T (3M) concept.   Much work has been done in the design of office chairs as a result of the general perception that ’correct Ergonomics of sitting safely’ is required for the avoidance of LBP.   In spite of the efforts of chair designers  prolonged sitting still results in backache.

The spine is only affected by the bio-mechanics presented to it.    An upright work mode can only be a partial solution  and can only go some way to meet the spinal Screen Shot 2018-11-28 at 15.32.37bio-mechanical challenge.      A knowledge of the 2T concept, a full solution, is helpful for the understanding of the following comments.   Hype and selling points, bells & whistles and apparent comfort are irrelevant.   I have yet to see any office chairs on the market that I could recommend for prolonged sitting although the information has been available since 1989.

A garden recliner.  It has only two positions.  Both are shown.  Simple but very comfortable with an easy, adjustment free transition.  It is a 2T system and provides a clue to the development of an office chair and is a forerunner of many of the principles expressed.
Screen Shot 2018-10-21 at 17.50.16

Screen Shot 2013-09-19 at 17.01.57Another garden chair, from France, which now claims to be a recliner and make zero gravity a selling point.  I approached them originally with this suggestion and heard no more. The  leg-rest retraction is interesting, simple and has points for a 2Tilt construct.

I do not know if their move was post hoc or propter hoc.

Screen Shot 2013-09-19 at 17.07.27
This young lady looks very happy!          But perhaps she would be happier with leg and neck support? →

Screen Shot 2013-09-19 at 17.08.56A common sight.  If he had correct neck support he could get on with some work.  Admittedly he would need a better computer screen, correctly placed.   Nice view!


Screen Shot 2013-09-19 at 17.02.39An example of a zero-gravity, reclining chair.  It has variable tilt and in the fully recline position the legs are above the level of the head. The headrest is adjustable and pelvic support is possible. The upholstery might give rise to heat build up.       See ☛Recliners→.

Screen Shot 2014-02-13 at 13.06.54

← Good in theory, but I have never actually dared to sit on one.


The Hermann Miller Aeron

HM1The Aeron chair has been chosen for consideration as an example of a top-range, highly engineered and carefully designed upright office chair. Originally launched in 1994 and  developed from an earlier study into furniture for the elderly, with a recliner chair as the inspiration, it incorporated a mesh construction in place of, the then, more common foam-filled upholstery.    I was impressed on first seeing this chair and wrote to the effect that it  could be seen in most design offices. I liked it’s ability to recline to 45°, as a step towards a 2T Chair, and the mesh construction and remarked that it dissipated heat build-up but also support, of which,at that time, there was none.    It shares the same biomechanic problems as any other mid-upright chair.   Like them it seems to have reached the limits for remediation with only limited success.

The late John Jukes, who was investigating the incidence level of office musculo-skeletal symptoms, wrote to me “The ergonomic stress symptom pattern is no different to the average office chair.   He also told me that he suggested to them that Gorman’s ‘pelvic support’ should be incorporated in their office chairs HM2but said this was ignored at that time.  Perhaps annoyed by his rebuff, having at last achieved a form of pelvic support, he later wrote “Henry.  A large percentage of staff throw out the lumbar support bar because it is too hard and uncomfortable. They do have a pelvic support now. However it has the same problem in that the support is concentrated at the base of the spine and not the iliac crest.”  He later wrote “It now incorporates pelvic support and so can be regarded, with reservations, as offering a semi-partial solution to the problem of LBP”.     Screen Shot 2013-09-29 at 18.33.37The Gorman design,  suggested to them by John Jukes in the first place might have saved them and their clients, 2 decades  of trouble.    Gorman’s “Pelvic Posture Principle” is not generally understood and pressure is still directed above the pelvic brim and to the midline and not to the iliac crests. ☛Pelvic support

Evident in the photograph, above, the seat is convex, an example of the ‘Off Load’ system’ which the Makshous study showed to have biomechanic advantages.    The convex front half goes a little way to being a FTS accounting for  some users admitting that they usually perched on the front edge. This seat shape allows this chair to be upgraded from a simple upright chair.

Mirra 2 HMThe pelvic support, included with the ‘Off Load’ system, is the only component of the Hermann Miller, and other, ranges that can lift these otherwise well designed chairs from at least one of the seriously adverse effects of the common upright chair (‘machines for making backache’). The back support only becomes ‘iliac’ at it’s lowest adjustment,  A more user friendly plastic band whose depth can be adjusted replaces the uncomfortable adjustable (usually wrongly) rod.  The back view shows that it is still slightly too high and likely to act as an adverse lumbar support.

Screen Shot 2018-06-08 at 19.53.52The new Lino chair by Herman Millar mentions  sacral support, which ‘nudges you into better posture’.    “…the cleverest way is a design feature that subtly corrects your posture so that the chair doesn’t need to be adjusted so much—and thus doesn’t need all the moving parts that make other task chairs expensive.”  (This sounds as if they have read this work.)  A step in the right direction, at last, some 20 years after the recommendation of Jukes.  The photograph is of one of the co-designers, Sam Hecht of Industrial Facility, photographed by Gerhardt Kellerman.

The OKAMURA ATLAS chair & Cruise concept.

Okamura Atlas“Looks familiar, Henry?” was the message from John Jukes about this office chair.  Sure enough it showed the semi-reclined work position that I had been advocating since 1998.  Ten years after my original suggestion, Okamura has recognised the importance of a reclined mode in their Cruise concept. However, the 2T concept has additional requirements for it’s implementation to be effective for an office or work chair and not to be simply a recliner or a ’zero gravity chair’.

okamura1Screen Shot 2013-09-28 at 21.30.29The designers had probably not seen the principles that I had formulated and tested at Cambridge, to make this mode optimally functional.   In my opinion, the reclined mode made this chair the best on the market at that tme. It has plenty of room for improvement. For further consideration see ☛ Okamura Atlas→


 It includes some of my 2T points.  Okamura had, by now,  seen my ‘Sitting Safely’  (protected by an nda) and it is possible that the designer, Giugiaro, had also seen it too.

The OKAMURA LEOPARD chair       

Okamura LeopardNot intended as a work-chair, it is aesthetically superb and looks right, however the fixed head-rest is only excellent for contemplating the ceiling.      A forward tilt is possible but there is no contouring to prevent slipping and it seems to be used for rising from the chair.   The intermediate range is stiff which makes it difficult to fully recline.   The seat is fixed at a low level.  This allows the feet to rest on the floor in the reclined mode, as shown.  I am told that this causes problems for tall people who have tried it and an adjustable table may be required (no bad thing).   Essentially a waiting room chair, jt would ne unsuitable for office work.

Pledge BT3 20/20 (Task)

Gorman, an engineer turned chiropractor, worked with PLEDGE to produce office chairs incorporating pelvic support.   Controlled trials by John Jukes of VESTRA showed them to be significantly more effective in reducing back shoulder and neck pain, compared with similar chairs. and advocated the Pledge BT3 20/20 (Task) pelvic support chair to reduce LBP problems in the optimised office environment.   These office chairs, incorporating Gorman’s ‘pelvic (actually ‘iliac’)  support have been in use over the last 10 years and some 40,000 are in use.  It has been estimated that considerable savings  Screen Shot 2013-09-29 at 18.34.21Screen Shot 2013-09-27 at 22.34.23have resulted due to reduced absenteeism and increased staff performance due to the improved ergonomics (Jukes J).  Initial outlay of cost is also considerably less than the two chairs considered previously.☛ Pelvic Posture→

The Howarth Zody

This is another good upright office chair that incorporates ‘Pelvic Support’, here called  PAL™.  This allows it to be considered as a semi-partial solution for full Safe Sitting.

  • Haworth ZodyAs with any upright chair it has the inherent disadvantage of the increased axial loading.
  • It has the advantage of a forward tilt mode and a possibly adequate pelvic support in the upright mode.
  • It boasts high engineering, ergonomic research based on maximising comfort and many adjustments, bells and whistles.  ‘200 test persons have adjusted the support in the lower back region again and again until they felt comfortable.   The sensors provided the scientists with data which they evaluated using pressure mapping technology. The procedure was repeated several times and the results were clearly confirmed.’ All probably excellent but totally irrelevant for full biomechanical requirements.  See ☛ Comfort?→
  • To some extent this has been addressed by incorporating a pelvic support system. This fails as it is adjustable and does not have the comfortable V-shaped iliac support of the original Gorman ‘Pelvic Posture’ concept.
  • Questionably it also incorporates lumbar support. If adjusted to produce effective lumbar lordosis this would counteract the important pelvic support. Adjustment to reduce this effect is counter intuitive.   In my experience adjustments are usually made in the wrong direction.  People have preconceived ideas as to what ‘should’ be correct and can be misleading in efforts to determine what best addresses the  bio-mechanical imperatives.
  • Adjustment of the seat surface up to 7 cm to the front and back is irrelevant.  Only the ischial tuberosity must be supported.  Limitation of the backrest’s opening angle to six steps is also irrelevant. Ideally this should adapt to the full reclined mode and intermediate steps avoided.
  • When shifting the weight to the front, the seat surface follows with a slight inclination downwards.  This is good. If this was the only mode, then many of  the other supports and adjustments would become irrelevant….
  • Memory foam seat.  Excellent. A strong + point when tilted forward.
  • Only really suitable for short term sitting.

The Albion range

Screen Shot 2018-12-06 at 11.41.44Screen Shot 2018-12-06 at 11.42.47There is a wide range of reasonably ergonomic office chairs.   Their Spynamic range claim extra ergonomic advantages. The chair shown on the left has a somewhat over long seat-pad but is is bettered in the example on the right.   It looks as if there may be messy unneccesary adjustment controls.


Screen Shot 2017-05-08 at 15.03.35Ferrari gets into seating

Peter Bessey sent me this ref. with the comment “Guess they missed an opportunity to work with your specs, Henry.   Would have been interesting to see them come up with a properly engineered solution, alongside the carbon fibre composites.   All the best,  Peter”      

Yes.   Only really suitable for short term sitting. HAS


The Modern Zure Office Chair

Screen Shot 2018-06-22 at 19.17.18“Boldly going where no chair has gone before. The Zure takes you to a new comfort destination. Our unique range of this distinctive, uber stylish posture perfect seating solution has it all.  There is fine mesh, fully upholstered, partly upholstered and stunning flexible elastomer options. The seat and backrest are carefully contoured to provide maximum comfort.   The high-quality outer skeleton wraps the user in touch point technology. Padded armrests on the fabric and leather options provide pleasing eye-appeal whilst the elastomer versions have colour coded armrests.”  “Orthopaedic designed frame”.  Having bought the hype and the chair for $736, the user would be well advised to study BACKACHE? For users and patients (only)  if prolonged use is intended.   Only really suitable for short term sitting.

A selection from ‘Posturite’.

Screen Shot 2016-06-12 at 14.02.18

A good selection but only really suitable for short term sitting.

 Dynamic seating & motionWobble ball

The basic model in this category is the ‘Wobbly Ball’.  A good idea but who wants to sit on this in an office?  So let’s call it a ‘Balance’ chair.

Swing seatThe SwingSeat from SmartMotion Technology

Basically an upright chair. With the seat forward tilted, lumbar lordosis is ensured.   It’s self adjusting controls allow a range from about 40° of reclination from the upright to a 10° of forward tilt which is performed effortlessly, avoiding the usual confusing plethora of adjustment controls.  Manual controls are present for backrest height, angle, depth, resistance and seat height and armrest control.  The concept behind this design is to enable constant small amplitude spinal movement which helps ensure the pressure gradients required for adequate nutrition of the disc.   The ergonomic evidence for the importance of enabling movement which is comforting and ensures health of the disc constituents is summarised by Rani Leuder in Ergonomics Review of The Swing Seat  See  Lueder R. Anatomical, physiological and health Considerations relevant to the SwingSeat. 2002; Ergonomics Review.  She is President of Humanics ErgoSystems, ☛→

The PESKA chair
Screen Shot 2013-10-19 at 17.40.18This ‘dynamic’ chair  has the option to fix the balance mechanism. It recommends sitting on a balance chair only for a limited time, say 3 times a day for 30 minutes. Sitting on office chairs with active balance mechanism throughout the day would be the same as if you exercised continuously for 8 hours.  The same effect occurs with the unstable intermediate mode in the 2T concept, but with stable positions at the end of ranges there is no need for adjustment.

screen-shot-2016-09-21-at-20-44-26The KOEHL AIR-SEAT, from Holland.

“Stimulates multidimensional micro-movements and trains by frequent changes the low-lying back muscles. Balancing on the KOEHL AIR-SEAT by gentle lateral pelvic movements, by a pair of air cushions.   Emphasises the rehabilitation function.  Comforting and aids IV disc nutrition which helps avoid early disc degeneration.

WAGNER chair

The Dondola hinge system allows a controlled all-round instability and a trial when incorporated in a Wagner chair showed reduction of morbidity when compared to office chairs without the system.  A full account is given in  ☛ EXERCISE & movement→

the BackStrong ChairBackStrong Chair

An awful example of OTT hype tells us that “this chair is’ the best in the world’ and ‘This means disrupting the seating industry -‘.  It was helped designed by ‘Dennis Colonello (D.C.), the top Chiropractor on Earth:.   See this at → BackStrong Chair

It appears to be an upright chair, needing a desk for work, This is likely to prove retrograd, even Dickensian (See Bessey in OFFICE WORK-STATIONS), in a few years when deskless chairs, as part of a sit/stand workstations, come on line.   As an upright chair it remains only a partial solution to the  bio-mechanic ill effects of proloned sitting. It’s remedial  points are :-

  • dynamic seating.   Called here ‘ Sit-In-Motion’.
  • A forward tilted seat (The FORWARD TILTED SEAT (FTS). )
  • This is helped by an independant moving seat pan.This reminds me of my 2013 Cambridge student model (See OFFICE WORK-STATIONS ) which is actually a full work station incorporating the 2T concept.
    • Screen Shot 2018-11-24 at 10.29.33This seat has the components to progress it to bio-mechanic (ergonomic) fully remediated office chairs for prolonged work.
    • I would urge the manufacturers to take advantage of this option which would result in a truly disruptive system that would sweep the chair industry.  Who wants to use a work-chair that is not ergonomically optimised?
  • Worrying is that the back support appears to extend above the pelvic brim.  In the verbal blurb it is described as ‘lower thoracic’ which would be bio-mechanically adverse  (See BACKRESTS. Pelvic support v. Lumbar.)..  Perhaps it would be as well if ‘the top Chiropractor on Earth’ had a word with John Gorman who is also a chiropractor with the advantage of a prior top engineering degree from Cambridge University.   Chiropractors are deeply suspicious, perhaps with reason, of us physicians.  I was trained by James Cyriax the ‘Father of Orthopaedic Medicine’ who wrote a book fiercely attacking Osteopaths and Chiropractors.  However Gorman overcame his suspicians as I discovered that he knew his spinal anatomy and bio-mechanics and we were speaking the same language.
  • Yet another “radically new” development which isn’t new except to those who came into the business recently (ie less than 30 years ago)”.  Unattributed, but guess who?
  •  In the present form it should probably not be used for longer than 6 hours.

chairsix‘ChairSix’ by Si Freeman

The design is sophisticated and simple – good.   The backrest is adjustable and can be adjusted to the adverse ‘lumbar’ position. – Bad.    Height location is critical. ☛ BACKRESTS. Pelvic support v. Lumbar.   The width of the back rest could be a problem for work-related activities.   If at a desk or table, its width impedes the elbow for keyboard and mouse activities. This issue was well-proven many years ago, by the design of chairs stretching back to Fred Scott’s Hille Supporto chair, where the narrowed spinal backrest was a deliberate feature and seems particularly popular in Scandinavian furniture designs still.     The seat(s) seem to be forward tilting – good.   The somewhat flexible, rubber foam pads which sit proud of the pan, on raised platforms, act as small pivots that adjust the pads to the body form and seemed to work well and gave a sense of flexibility and comfort to the seat pan. – good.      The 6 knobbles on the back-rest,may represent some type of ‘massage’ feature, as seen on some Asian add-in seat pads for vehicles and office seating and that the slight wobble from the pivoting pads, also provides the movement needed to move the back against them.  They are not in the mid-line – good.

It seems to me that ‘Pelvic Support’ and a FTS are not complementary but ‘either or’.  The  ISCHIAL OFF LOAD system gets round this with a convex seat-pan providing a FTS in front and slope towards pelvic support at the back.     In spite of these improvemrnts this remains an upright chair with their considerable ergonomic disadvantage.   Only OK for shortish sits as in a sit/stand office.  ☛ Sit Stand & stools

Cobhamly High Back Mesh Office Chair

Screenshot 2019-11-07 at 16.05.12

I have not seen this chair.  It seems to have ‘pelvic support’,   although possibly above the 20cm allowed height.   The price seems OK.   Their Boston High Back Executive leather effect operator chair. Features a heavy duty gas seat height adjustment and fully synchronised tilt to seat and back rest with adjustable tension control.   I do not know how this works out, But could probably be adjusted to comply with the 2T concept with optimised comfort.   It has features that suggest that the designer may have seen this blog.






AN EXISTENTIAL THREAT – A new breed of office chairs with a reclined work mode.

WORKCHAIRS, a new breed with a reclined mode.

As predicted this is begining to emerge.  A number of ‘workstation’ type office chairs are appearing which include a reclined work mode and so are superior to the present (2016) upright conventional upright models.  Appearing to ignore the science and based on engineering they do not invite a great uptake inspite of extensive PR.

AltmarkNow, in 2015, an office chairs is proposed, the Altwork  that has at least an upright and reclined work position as I had been advocating since 1998.  However, it fails the functionality of the 2t optimisation.   These faults could easily be corrected and so  with reservations, it is  potentially the best work-chair in the market. See a more detailed account in  WORKCHAIRS, a new breed with a reclined mode.→   .    .  also (

The Cambridge trials showed the elegance, simplicity, cost effectiveness  and greatly enhanced ergonomics of the 2T concept.  This provides an opportunity for the existing manufacturers and any entering the field.   Top manufacturers are already recognising that they have come to the end of the line for ergonomics. Backache (LBP) and other spinal & muscle-skeletal conditions still persist resulting in stress and lowered productivity.

BACKACHE? For users and patients (only)

OK.  So you use a chair and are liable to backache.   All this is very confusing and so what do you do?    I am no longer in the business of giving advice to patients and organisations.  However my interest in optimising chair design might allow me to offer some tips for users and patients (only).

Possible remediation.

If you have an expensive, top range chair or a cheap one, examine the section on how some of these relate to the 2T concept.  A good chair can be modified to approach the advantages of the 2T CONCEPT (see 2T CONCEPT a full solution →’).   This may help you modify your own chair.

  • Disable the adjustment that allows the pelvic support to be above 20 cm above the seat (?Chewing gum)    (see ‘Lumbar, pelvic/iliac support’)
  • Arrange for the adjustment control to allow easy back & forward movement.  Make the chair a 2T system – either reclined or forward but not intermediate. (Unstable intermediate mode→).
    • Intermediate ranges should be unstable.   They can be used as a rocking chair or as  therapeutic exercise following an acute episode of backache/lumbago.
  • In the upright mode the seat can be either tilted forward (see ‘The forward tilted seat), or arranged to take advantage of the pelvic support providing this is correctly modelled or a combination of both.
  • Apart from chair height and head/foot-rest, adjustments should be set accordingly and then ignored or fixed.
  •  If you are buying, a back shop can show a number of models and advise but be aware that they are trying to sell you something and tend to feed you the manufacturers hype.

If your chair is really basic you may need some widgets. Possibilities are

  • A wedged cushion on the seat which helps approximate to a ‘Forward Tilted Seat’ (FTS).  See  .Why? Mandal’s Homo sedens. The concept has been fully confirmed by research using pMRI scans.   See short account below.
    • Screen Shot 2016-05-10 at 20.14.08One I assessed, from America ªSITTS Posture Cushions.)  and wrote ” The seat pan is parallel to the floor (checked) but with some contouring that might add  2° .   The hip angle is shown to be 132° which is close to the optimum angle (130°) determined by pMRI studies to avoid  adverse movement of the Intervertebral disc contents (Smith FW et al. The Response of the Nucleus Pulposus of the Lumbar Intervertebral Discs to Functionally Loaded Positions. 2007;SPINE Volume 32, Number 14, pp 1508 –1512).  See → Positional MRI
    • The above confirms the views of AC Mandal  which he advocated in his book (Mandal. AC., The Seated Man (Homo sedens). 1985. Dafnia Publications,) are confirmed   He advocated a seat that was tilted forward and down by 20-30° from the horizontal, allowing the hips to extend to 120-130˚ and the pelvis to tilt forward with the lower spinal joints adopting the correct, safe, lordotic posture.   
    • With the seat tilted forward, note that the user is not constrained by a backrest and is free to move, the lumbar lordosis is maintained by the pelvis being tilted forward.   The versions with a steeper angle may have a problem with slippage.     Now in 2018 since writing the above on an early version, new improved  ones have been developed by SITTS.   They look good and can be seen at Or→ (
  • A backrest cushion that gives iliac support.  Have a good look at the section here on iliac support that must not be higher than 20 cm above the seat and approximates as near as possible to the original Gorman model.
    • My patients loved the ‘PostureRight’ cushion which was designed by my old St Thomas’ colleague, Dr Bernard Watkins.
    • Various lumbar ‘Rolls’ are OK if correctly placed.
    • I have a cheap (£1) and cheerful wire & net model which works moderately well.

Remember the importance of exercise & movement.    Good Luck!

Screen Shot 2018-11-28 at 15.32.37There is plenty of well intentioned advice on backache to be found on the web.    But please read this first (Sorry, hard work, I know) so that you can distinguish the  rarely well informed from misinformation  and hype, some that is frankly laughable.  Just have a look at Google→.

The Hermann Miller account from being almost laughable is now good, probably as a result of being advised by Andersson, the Swedish scientist. I find the latest (2015) account too diffuse to be easily comprehensible and illustrates some retro models.

JD Gorman’s holistic/ chiropractic account can be seen at ‘Natural Joint mobility’.

Some is linked in Backache and GENERAL USERS

Screen Shot 2018-06-03 at 18.19.49

How other people sit

Better!   But not for office work.


Screen Shot 2013-09-26 at 22.51.16The Japanese kneeling posture, like most things Japanese, is highly sophisticated.   It is elegant particularly when a Kimono is worn and for women the firm Obi also provides support.   The body weight rests on the heels of the extended feet so that the hips are extended at a slightly greater than a right angle. This allows the pelvis to rotate forwards, as with a forward tilted seat, resulting in  a lordosis at the lower lumbar joints.    The torso can remain comfortably upright as in the modern, forward tilted Scandinavian Balans chair.Screen Shot 2013-09-24 at 19.24.16


Screen Shot 2013-09-26 at 22.51.43The Japanese, like most people of the Far East, have hyper-mobile joints but the more hypo-mobile Europeans find this position uncomfortable to maintain as it requires extreme forced flexion of the knees and extension of the ankles.    Frequent and prolonged use of this position results in callus formation on the dorsum of the feet.



When I asked this Icelandic girl to sit to have her neck examined, she adopted the Japanese sitting posture on a chair.   When asked “Why?” she answered “Because this is the way  that I have been taught by my Physiotherapist.”  Note that her hips are extended to a near FTS extent.

The traditional Japanese sitting posture was shown in a study (Schlemper 1983) to cause less back problems than sitting in a chair but increased as upright Western seating was introduced.

Various sitting and standing postures were measured for degree of lordosis and electrical muscle activate (Dolan, Adams 1988).    The results confirmed that of the sitting postures, the Japanese involved the least flexion but the most muscle activity to maintain, whereas  slumped sitting on the floor  involved much greater lumbar flexion but very little more muscle activity than standing.

 The slumped and squatting positions are used by most non-Western peoples and who tend to have a low incidence of LBP (Fahrni  1965, Jonck 1961) , the wedge shape of the vulnerable lower two lumbar joints (L4/5 & L5/S1) is preserved although there is flexion throughout the lumbar spine  (Bruggeman 2000).   Intra-abdominal pressure maintained by the abdominal and spinal muscles acting through their flat tendons and fascia and the upper body weight is brought forward to lie over or in front of the abdominal cavity which can be regarded as a balloon or football,  This has a pressure relieving effect on the spine and transmits a proportion of the upper body-weight  directly to the pelvis.  Gorman has also pointed out, this position exerts traction on the lower two lumbar joints, so that although the joints are flexed the compressive force has been reduced.

To review the bio-mechanic problems that occur with sitting and their ☛Remediation⟶

Next, some side issues, ☛ Why?  Mandal explains⟶


Ergonomics of sitting safely.   How we sit now is badly!  The recommended ‘correct’ posture  being almost impossible to maintain, most of us sit in a posture that can be shown to invite spinal breakdown.

The photographs show a group of doctors and physiotherapists who are attending a course on orthopaedics.    Most are sitting slumped with rounded back. This allows the pelvis to tilt backwards and  stretches the posterior ligaments but is not as adverse as sitting bolt upright as currently advised and is nearly impossible to maintain.




The chair seats are parallel to the floor so that an upright posture must entail flexion of the hips at a right angle.   The lumbar lordosis is lost and  the adverse flexed position of the lumbar joints occurs which can be clearly seen.   Crossing of the legs accentuates this.   Note that none is using the backrest except for the doctor in the white shirt  who is in a semi-reclined slouched position.  In this mode the lower lumbar joints may be unsupported and flexed (but see below) and the posterior ligaments are stretched but the intradiscal pressure is reduced from 0.44 MPa to 0.27 MP as shown in a study in Ulm by Wilke (Wilke 2001).  If fully supported this is moving towards the 2T (3M) concept of  a reclined work position.  WWSN.4

 The physiotherapist in the check shirt is sitting forward on his seat in order to extend his hips slightly.    The table is too low for him and so he loses this advantage as he has to  bend down towards the table top.  In Wilke’s study bending forward about 20° with straight back and without arm support increased the pressure to 0.63 MPa up to 0.83 MPa, which was reduced  to 0.43 MPa WWSN.5when the elbows were supported.   The physiotherapist in the striped shirt has adopted  an extended position as he is able to brace himself with his arms.  This has the added advantage of forward rotation of the pelvis and so protection of the disc wedge angle. A work position, of this sort, was found to be the commonest (52%) in the quick study (below).   In the next picture I am seen using a stool shaped like a saddle.   My hips are extended but this advantage is lost as the table is too low.  A saddle seat becomes uncomfortable due to localised IT pressure. This happens less with the equestrian saddle due to movement. 2013, Practicality & ergonomics of sitting safely.

A pilot study, in 2013, of how we sit now by students, at Cambridge, working on a project for a 2Tilt chair in relation to desk interface  and office space indicates results, from a nearby office, that might surprise some people.   This was occasioned by the somewhat confused results of intradiscal pressure studies where there is a variation in sitting positions and units used and is also relevant to the single pMRI study (Smith 2006).  A more complete study is required.

Screen Shot 2013-09-24 at 19.25.36






Note that in the absence of reclined work chairs only15% + 3% were sitting upright.

The slouch.

Another reprehensible posture –  or is it?

Screen Shot 2013-10-23 at 14.22.53The popular slouched or slumped posture when sitting in an upright chair looks very wrong if  the misconceived ‘correct’ sitting posture, as excoriated by Mandal, and confirmed by the correct ‘preserve the lumbar lordosis’ dictum is accepted,   It is assumed that this posture will cause LBP if without support at the lumbo-sacral level. This may be true for Western societies where children have been universally accustomed to sit in ergonomically unsuitable upright chairs. This is an oversimplification when non-western sitting is taken into account.

slouchThe diagram shows that the flexion occurs at the upper lumbar joints with normal, or increased up to 40°, kyphosis of the thoracic spine. The pelvis lies fully on the surface of the seat and cannot tilt backwards.  The two lower lumbar joints, where IV Disc derangement typically occurs,  are safe if the wedge angles preserved.   The position is not very different from that in a semi-reclined chair.   In the 2Tilt (3M) version emphasis is placed on correct support from head to feet, with a slight degree of iliac support to prevent sagging at the lumbo sacral junction.  Wilke  found the L4/5 intradiscal pressure to be 0.27 MPa against  0.45 to 0.50 MPa when sitting upright (Wilke 2001).

The modern epidemic of backache is associated with lack of exercise and, In spite of uncertain epidemiological  evidence, prolonged upright sitting in chairs.    This is a relatively modern habit.    High backed chairs were an article of state and dignity.    Even monarchs used their thrones for limited and specific events.  Most people sat or squatted on the floor in various ways, which were culturally determined, and  benches and stools were the ordinary seats of everyday life.   It was in the 16th c. that the chair ceased to be a privilege, and became a standard item of furniture for anyone who could afford to buy one and the chair speedily came into general use and that is how we sit now.

Joint stoolJoint stool. These were made in large quantities in the 16th and 17th centuries. They were the most common form of seating before chairs became universal.  Users tend to perch with hips extended as recommended by Mandal.  People did not seem to be bothered much by backache. They were erroneously called ‘coffin stools’ in the 19th century.    Shown are two late 17th c. models.

Next see ☛ How other people sit

And   ☛ Various chairs.  How do they measure up? →  

See also a lighthearted account of the Victorian office. which also includes an account and treatment of RSI (WRULD).