Various chairs. How do they measure up?

My remarks are intended only to illustrate points in relation to the 2T concept.

They are not intended to imply either a recommendation or that any of these chairs may be in any way unsafe.  The points made are related to the evaluation of bio-mechanical factors.   Some links provide access to manufacturers website so that their range and hype can be compared.  Some knowledge of the biomechanics is helpfull.

Screen Shot 2013-10-23 at 14.04.26Much work has been done in the design of chairs as a result of the general perception that ’correct ergonomics’ is required for the avoidance of LBP.   On talking to designers I find that they aim for comfort, that treacherous guide  which only turns up truthfully when the bio-mechanics (ergonomics) are fully correct”. (See  ☛Comfort→.   ) Familiaity bias (cognitive dissonance) is also a hindrance ( ☛  Familiarity bias→.).

 Simply, prolonged sitting still results in backache.

Memo to a general reader.

Screen Shot 2015-12-16 at 14.05.16Superb engineering and visual design are fine but are not understood or appreciated by the actual spine.  The spine is only affected by the bio-mechanics presented to it. Essentially, with an uprigh work mode, these chairs can only be a partial solution to reduce mechanical spinal disability and can only go some way to meet the spinal bio-mechanical challenge.    Hype and selling points, bells & whistles and apparent comfort are irrelevant.   Essentially, with an uprigh work mode, these chairs can only be a partial solution to reduce mechanical spinal disability and can only go some way to meet the spinal bio-mechanical challenge.    Hype and selling points, bells & whistles and apparent comfort are irrelevant.
At present real, but partial, safeguards are only

  •  a Forward tilted Seat
  • or pelvic (Iliac) support.   These  have to be designed with precision to be effective.  This is often not fully understood.

A knowledge of the 2T concept, a full solution, is helpful with the understanding of the following comments.Screen Shot 2016-06-29 at 14.17.13


A garden recliner.  It has only two positions.  Both are shown.  Simple but very comfortable.

recliner1    recliner2 There is no shaped back support, having been designed before the importance of this had been appreciated.     It provides a clue to the development of an office chair and is a forerunner of many of the principles expressed.

Screen Shot 2013-09-19 at 17.01.57

Another garden chair, from France, which now claims to be a recliner and make zero gravity a selling point.  I approached them with this possibility and heard no more. The  leg-rest retraction is interesting, simple and has points for a 2Tilt concept.

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


Screen Shot 2013-09-19 at 17.07.27This young lady looks very happy!

But perhaps she would be happier with leg and neck support?


Screen Shot 2013-09-19 at 17.02.39Another excellent, 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 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.

Screen Shot 2014-02-13 at 13.06.54

Nice view!


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


HM2The late John Jukes, who was investigating the incidence level of musculo-skeletal symptoms in offices, told me that he suggested to a leading manufacturer that ‘pelvic support’ should be incorporated in their models but said this was ignored.  Perhaps annoyed by his rebuff by the firm, Jukes 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, a decade  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→.

The Hermann Miller Aeron

HM1Aeron chair has been chosen for consideration as an example of a top-range, highly engineered and carefully designed upright 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.   It is essentially used as a mid-upright chair and shares the same biomechanic problems as any other upright chair. Again, 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.  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.  This has been subsequently added but could still benefit from further remediation.

Although the chair can be tilted back to about 45°,  reducing axial loading, it does not have the necessary head and leg-supports to make this a true working position.  The seat has a variable tilt which is related cybernetically to the backrest (Kinemat tilt) to avoid the necessity for fiddly controls (although many fiddly controls are still present). This may be good but is complicated and allows the adverse intermediate positions.   These are not allowed in the 2T solution, and also provide a ‘dynamic seating’ element.. The seat is convex and there is a backward slope of the rear half of the seat (evident in the photograph, above) which  brings the pelvis back into contact with the ‘pelvic support’ for this to function effectively.     The convex front half goes a little way to being a forward tilted seat (FTS) but seems barely adequate to be effective although some users admitted that they usually perched on the front edge and so achieved the advantage of a forward tilt mode. This seat shape is an example of the ‘Off Load’ system’ which the Makshous study showed to have biomechanic advantages which allows this chair to be upgraded from a simple upright chair.

Mirra 2 HMThe ‘MIRRA Chair. The pelvic support 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.

The OKAMURA ATLAS chair & Cruise concept.

Okamura Atlas“Looks familiar, Henry?” was the message from John Jukes about this 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’.

okamura1The designers had probably not seen the principles that I had formulated 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.

OKAMURA CONTESSADesigned and engineered to a high standard of sophistication but, again, there is a plethora of unnecessary controls which are so loved by contemporary designers.  Most  should be scrapped or disconnected by a user who is aware of the adverse positions on spinal pathology.

The brochure states, ”The lumbar support gives you comfortable support.  You can adjust the lumbar support backward and forward up to 15 mm , and up and down to 60 mm.”   The upright work position shown is acceptable as the ‘lumbar’ is actually  ‘pelvic support provided it cannot be adjusted upwards above 20 cm.’.  Gorman  showed true ‘lumbar support‘,above 20 cm, to have the opposite effect to that desired and later confirmed by pMRI scans.

The reclined mode is about 50° from the floor, a little short of the ideal 45° but acceptable. The figure given above is 26° from the illustrated upright mode.

It relies on the ‘off-load’ domed seat.   I prefer the forward tilted seat but know of no evidence that shows one system to be better than the other.

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.     Essentially a waiting room chair. 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).

Pledge BT3 20/20 (Task) Gorman, an engineer turned chiropractor, worked with PLEDGE to produce models incorporating pelvic support.

Screen Shot 2013-09-29 at 18.34.21Controlled 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 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 2013-09-27 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 is another good upright 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 an 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 Screen Shot 2016-02-14 at 18.18.00shifting 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.

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”


A selection from ‘Posturite’.

Screen Shot 2016-06-12 at 14.02.18


 Dynamic seating & motion

Wobble ballThe 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

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, ☛→

Basically an upright chair. With the seat forward tilted, lumbar lordosis is ensured.

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 a chair 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 Screen Shot 2016-02-14 at 18.18.00unstable intermediate mode in the 2T concept, with no need for adjustment.

The KOEHL AIR-SEAT, from Holland.

screen-shot-2016-09-21-at-20-44-26“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 the chair without the system.  A full account is given in  ☛ EXERCISE & movement→

the BackStrong ChairBackStrong Chair

The 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’.

From the photographs 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.
  • The back support is worrying.  It appears to extend above the pelvic brim.  In the verbal blurb it is described as ‘lower thoracic’.  If so, this 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.
  •  In the present form it should probably not be used for longer than 6 hours.
  • This seat has the components to progress it to a bio-mechanic (ergonomic) fully remediated chair 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?

“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?

I have not had the opportunity to see this chair and hope that I have not been unkindly prejudiced by the hype which is actually typical and for which the manufacturer may not be responsible. See this at → BackStrong Chair



As predicted this is begining to emerge.  A number of ‘workstation’ type models 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.

The ALTWORK chairScreen Shot 2016-06-29 at 14.17.13

AltmarkNow, in 2015, a chair is proposed, the Altwork  that has at least an upright and reclined work position as I had been advocating since 1998.  However, it fails 2t optimisation by not being unstable in the intermediate transitional mode.  This is important as it allows a user to  stop in the adverse mid-range for prolonged work with the potential for spinal damage.  It also may  prevent advantageous dynamic movement.  I am not yet able to assess the ergonomics of the backrest configuration.

These faults could easily be corrected and so  with reservations, it is  potentially the best work-chair in the market. (  Did they see my web-page for the 2T concept which has been in the public domain since 1998, later upgrade to the 3M (2T = 3M) & 4M the optimised default  against which the ergonomics of any chair can be assessed?  Or did they arrive at this independently?  I fear it was the latter and the chance of a simpler, more ergonomically optimised and more elegant model was missed.  Also the aesthetics worried me.  I penned a hurried post on this subject.(ALTWORK & Art →).

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.