Category Archives: REMEDIATION

The essential requirements to avoid backache (LBP) associated with sitting.

Familiarity bias

Familiarity bias is a factor in holding back the development of ergonomic seating.  Efforts at remediation of upright seating seem to have come to the end of the road. To address the epidemic of LBP a paradigm change is required.

The Ptolemaic system of astronomy seemed to make sense of what was observed in the sky above, that the earth is the centre of the universe.  It worked for 1,500 years even becoming a tenet of Christianity, until Galileo made the mistake of inventing a telescope and Copernicus showed, scientifically, that it was wrong.  The Christian was an example of familiarity bias.

There’s now new research coming out on what’s called the double split experiment, which is a major contributor to the understanding we have of quantum mechanics, which is now maybe violating the popular interpretation of that, 70 or 80 years after it was made.  Change can be slow.  Perhaps no bad thing.

People normally think that the experts are correct.  They have the top jobs and the top positions in the professions and universities, and so generally that’s true.  Until the next scientific advance arrives.  A scientist  at CERN explained “you know, so far my theory is safe, but it might – you know, ask me next week, they might have found out that I’ve been wrong my entire career”.   Good scientists are prepared to admit this but most people are overwhelmed by familiarity bias.

I find this bias pervasive among chair designers.  Peter Bessey comments in this work (→COMFORT)  “Introducing medical-based information to designers and their education, at an early stage in their careers, would be a good way to change the status quo. The question is: how do you get that over to them in a lucid and easily digested manner? It needs to be described and presented in an easily accessible manner and not necessarily couched purely in medico-scientific terminology.”  In other words, they are really not up to speed on the scientific evidence.  This bias is extended to manufacturers who are perfectly happy with the status quo.

The bias holdup  Normalcy bias

Failure to understand familiarity and normalcy bias is likely to lead to serious problems for firms, however big.    It is a dangerous trap for manufacturers of ergonomic office chairs to fall into and it can blind recognition to a very real and credible threat.

The general familiarity bias

Screen Shot 2016-03-12 at 16.07.46We are hardwired to believe the world we live in today and to which we are acclimatised so that we become incapable of comprehending and believing that change is coming.  In general most users have been commanded, since nursery days, to ’Sit up straight’ or worse ’Stop tilting your chair forward’, a normal response of a child to adopt an actual correct position.   Later  ‘expert’ advice on ‘correct’ sitting upright is given with authority.  This is inspite of having been demolished by AC Mandal back in 1985 (See→Why? Mandal’s Homo sedens. ).   This mistaken view of correct seating is still accepted and widely promulgated by authorities who advise on such matters.

'Correct sit

It is not surprising that most people have difficulty in over-coming the ‘familiarity bias’ engendered.  The exception are many backache sufferers and the younger, millennial, generation who are capable of thinking ‘sideways’.

My own initial training in Biology has made me mistrust sudden jumps (large mutations) in ‘natural selection’ as these are usually deleterious. It is small incremental advances over time that result in progress.  The same can be applied to political ideology which has made me a conservative.  However when real scientific evidence advances it may be time to change.

 Cognitive dissonance

Cognitive dissonance, described by Leon Festinger in 1957, is the condition described in psychiatry and describes the unease felt by people whose experience or information is inconsistent to other, usually already held, beliefs.  Information and situations are avoided  In an effort to reduce this discomfort and regain psychological consistency and is virtually equivalent to ‘familiarity’ and ‘normalcy’ bias.

The 2T or 4M concept, in terms of chair design is only an incremental change.  Most office chairs need only modifications.  But as a concept it seems to excite cognitive dissonance and be regarded as a ‘paradigm’ shift.

 Comment

Screen Shot 2017-03-07 at 17.59.30

From Prof. MC Boulter
The comments in your  interesting blog remind me of the theme that d’Arcy Thompson used to preach a century ago. He must have influenced you also.
Best wishes
– Michael

Screen Shot 2017-03-07 at 17.59.30     Reply from Dr HA Sanford 

d’Arcy Thompson, I think, had a mathematical approach to development and did not understand evolution by natural selection, which is my approach.  I see the 2T concept as an incremental change, along the lines of development by natural selection.   In the world of chair design the 2T concept is perceived as a ‘paradigm change’, a reclined instead of an upright posture, and I have to accept that as being so and say so.   These alternate viewpoints may make my explanation sound contradictory and excite cognitive dissonance.

Many thanks
Henry
Screen Shot 2018-05-03 at 16.15.51

WORK-CHAIRS, a new breed with a reclined mode.

As predicted ,  back in 1998, this is begining to emerge.  We see a number of ‘work-station’ type models which include a reclined work mode and so are superior to the present (2016) upright conventional  models.  The models shown here are not 2T compliant and appear to ignore the science and are based on engineering.    They do not invite a great uptake, inspite of extensive PR.

P Bessey writes (30/6/2016) “It has taken time for the market to build, but there is definitely a movement toward other postures in the workplace. While some of that has derived from posture investigation and potential for beneficial effects on the user, other advances have emerged as a response to changing technology, new materials and a non-paper work method, as seen from the 60’s onward.   I suspect that a NASA effect is involved in some of this too. Numerous resources have been directed into space travel in recent decades and, for human travellers, that has mostly incorporated a reclined support system to encourage stress-reduction during high-load take-off and landing. So there has been a real effort to ensure that anthropomorphic needs are addressed properly when working from that position, to ensure equipment control systems can be operated successfully and without long-term harm.   There have been a number of attempts to create pod-like structures around reclined positions, to create controlled environments for audio enjoyment, meditation and relaxation. Perhaps those too, have influenced the current trend? But the main factor may well just simply be the instant communication and data access that today’s world now has available for sharing ideas.  Apart from that, it is likely that this trend has derived from the typical and gradual process in which increased knowledge, enlarged awareness and advance in technology brings. Stale markets, where things have remained much the same for decades and highly competitive markets where a cycle of fashion and small detail differences are all the consumer sees on offer, can drive the introduction of disruptive design ideas and encourage new entrants to challenge the existing status quo. 

Perhaps that is what we are beginning to see?
Best regards  Peter”

 

ALTMARK

AltmarkNow, in 2015, a chair is proposed, the Altmark that has at least an upright and reclined work position as I had been recommending since 1998.  However deficient in biomechanics (ergonomic) optimisation, with reservations, it is  potentially the best work-chair in the market. (http://altwork.com).

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.

It also has a ‘stand’ facility so in this respect is approaching the 4M workstation→.  I have not seen this chair and so cannot assess the reclined configuration.   It incorporates iliac support (at least, I hope iliac and not lumbar), which is required in the upright mode but might be excessive for the reclined mode.  The reclined configuration can be deeply adverse as can be found in some dental reclined chairs.

   From the photographs it does not seem to be 2T compliant.  There appears to be intermediate  position adjustment in the transitional mode, which at best, gives no biomechanic advantage and was probably intended to add comfort → .   Misled by ” that treacherous guide  which only turns up truthfully when the ergonomics are fully correct”.   If this mode becomes a part of the unstable intermediate mode it allows a faster transition and also gives the user the choice for dynamic motion and rehabilitation.   Scrapping a fixed intermediate mode reduces manufacturing costs.    Not having had an opportunity to see this chair, I cannot comment further on the ergonomics.

Screen Shot 2015-11-06 at 18.21.33Although an expensive ( $5,900),It looks over engineered, awkward  and too clunky  for an ‘object of desire’.   I have ignored a discussion of the aesthetics as I thought that this could safely be left to individual designers.     With the ergonomics correct this could be left to market choice.   Perhaps i was wrong and so hurriedly penned an effusion of which I am not proud!    ☛Altmark and Art→

Now have a look at the Cambridge student project on the 2T CONCEPT. Simple, elegant & cheap.  The Cambridge trials showed the elegance, simplicity, cost effectiveness  and greatly enhanced ergonomics of th 2T concept.2T Deskless office chair

It excited much comment along the lines “Gee!  That’s cool.  I want it”.  The lack of ‘familiarity bias’ is typical with the millennial generation.  Go consider.

Ergoquest

Screen Shot 2016-06-24 at 12.34.17A good idea in that it achieves the 2 modes that I have been advocating since 1998, but what a terrible design!   Electrically operated.  With all possible bells and whistles It represents an almost opposite view to the 2T principle and it’s 4M workstation derivative.   This  with an emphasis on anatomy and spinal biomechanics leads to lack of adjustments and simplicity.  Obviously a huge misplaced engineering enterprise without awareness of what was possible and desirable.  Another example of what emerges when the the optimised default solution of the 2T concept is ignored.

Price: $5995

The CHOTTOScreen Shot 2017-05-20 at 11.14.27

This highly innovative chair was introduced to me by it’s designer,Thomas Stroman, the Founder of Stroman Design.   He wrote to me “I am an architect by training, but having experienced back surgery, my focus has been on ergonomic seating design for human-computer interaction.

At first glance I might be excused for thinking that it looked as if it were self mobile with caterpillar tracks.  Perhaps an exciting concept for the future. What fun to go charging around the workspace and bumping one’s colleagues!

Screen Shot 2017-05-20 at 11.11.16The importance of a reclined work position has been recognised.  It could be modified to become virtually 2t (4M) ergonomic compliant.  A foot rest has been incorporated,

→  www.stromandesign.com

REMEDIATION

Screen Shot 2016-02-14 at 18.18.00The main adverse effects of upright sitting have already been covered and are recapitulated here.  Once  recognised then it becomes possible to consider the options available for remediation.   This is a resource for the design of chairs to avoid the associated LBP.   It should be an essential tool for any chair designer

The adverse effects of upright sitting.

Screen Shot 2016-03-13 at 15.11.47This has already been covered in ☛Biomechanics→.  For greater detail and Recapitulation.  AVOID :

  • The intradiscal pressure from spinal axial loading in the upright state. The conventional upright sitting posture increases disc compression.Reduction of axial loading→
  • terminologic shiftRetroversion (backward tilt or to an an anatomist a ‘forward tilt’)  of the pelvis results in lumbar spinal flexion which reduces or reverses the protective disc wedge angle.avoid backward tilting of the pelvis→
  •  Preserve the lumbar lordosis→
  • Stretching of the posterior elements (ligaments joint capsules) allowing instability of the motion segment and can lead to CTD.  Ligaments→
  • AugmentedA reduced hip angle.  With a seat parallel to the floor the hip angle at only 90° the hip extensor muscles (hamstrings & glutei) also rotate the pelvis so as to flatten the lumbar lordosis.
  • The lower lumbar intervertebral joints (L5/S1, L4/5 & less, L3/4), on the mobile side of the lumbo-sacral junction, being the most at risk
  • Localised pressure in the area of the ischial tuberosities (IT)
  • Immobility.  Ensure disc nutrition by pressure changes with movement→

Mandal.  The Seated Man→  Also See ☛Lumbar v pelvic support→

Check back and review ☛ BIOMECHANICS←

 Next consider the  Requirements for  REMEDIATION & optimisation.

Partial solutions in use at present  include

These partial solutions are for mid-upright sitting in chairs that have been well designed and engineered.   However they are not a solution to fully reduce  the incidence of backache (LBP).   This would require a new technical fix that addresses all identified adverse bio-mechanics effects of prolonged upright sitting and is described under  ☛ The 2 TILT (2T) CONCEPT

Partial solutions

  1. The ‘Supine reclined mode’, if correctly configured, is the only position that addresses all the requirements for remediation shown above.  It provides the default working position for the 2T (3M) concept.   For the 2T full remediation further requirements are necessary. These may be lacking.
  2. Back support of some sort.         ☛ Lumbar v Iliac support→   
  3. Forward Tilted seat (FTS)     ☛ The FTS→   ☞ Mandal
  • ‘Ischial off-load   A third system, combines these two. by use of a convex seat.   This combines both a FTS and allows, at the back half, pelvic support.

 

 ALTERNATIVE SYSTEMS

Wobbly chairsSit/Stand.       For more detail See ☛Sit/Stand→

The negative consequences of constrained sitting has been described by a number of authorities (Adams and Hutton, 1983Duncan and Ferguson, 1974Edlund  There are advantages in keeping staff moving around and inter-reacting in certain types of office.  Note that a sit/stand system can always be incorporated into a 3M ☛ work chair station→ .Dynamic seating.   For a fuller account see ☛Movement→

Spinal movement aids muscle proprioception and IV Disc nutrition which has a physiological advantages over constrained seating and also may have a comforting effect if under the control of the user.         Also ☛   2T exercise systems→

‘Dynamic Seating’

Screen Shot 2016-03-14 at 13.35.24There is a recognition that prolonged constrained static postures are uncomfortable and deleterious for both spinal and general health.   Recently there has been interest in continuous small amplitude movement for upright chairs, the chair re-aligning with the users centre of gravity,  and termed  ‘Dynamic Seating’.     Exercise is required to maintain this position This provides proprioceptive feedback and frequent small amplitude pressure changes which may be comforting for short periods and helps multifidus muscle action. Rani  Lueder  gives a review account (Lueder R 2002) and the referenced evidence→ is considerable.     A few chairs are considered in this respect → various chairs. How do they measure up? .

COMPLETE SYSTEM for ergonomic optimisation (and comfort).

The 2 TILT (=TriModal, 3M) chair CONCEPT.

A complete solution.  An optimal system that effectively fully remediates all the adverse effects that have been enumerated.  Any chair can be compared for establishing the ergonomic efficiency.   An essential tool for chair design.        See ☛ The 2 TILT (2T) CONCEPT

Requirements of the 2Tilt concept.

  1. Screen Shot 2016-03-18 at 18.08.46A reclined mode for prolonged work    ☛2T reclined mode→
  2. An upright mode required for certain jobs.    ☛2T Upright mode→
  3. An unstable intermediate mode to enable a quick, easy transition between the 2T modes.    ☛2T transition mode→    ☛ dynamic seating→  With the recognition that the transition movement has physiological advantages, this has been upgraded to a ‘mode’.  The 2T now becomes a triple-mode (3M) concept.
  • A sit/stand facility can be incorporated to become a 4M version.    ☛Sit/Stand→

Screen Shot 2016-03-18 at 19.28.20

BACKRESTS. Pelvic support v. Lumbar.

Correct BACKRESTS.  A partial solution.

Correct pelvic support prevents the usual backward tilt of the pelvis which flattens the protective lumbar lordosis.   The emphasis is on ‘correct’.  

  • Pelvic (iliac) support.  Of fundamental importance for any chair design intended for prolonged use.  Support is directed at the level of the pelvic Iliac crest, approximately 20 cm above the seat.
  • Lumbar support.   Support is directed to the lumber spine above the iliac crest.  it fails to prevent backward pelvic tilting and can be seriously adverse.

Pelvic tilting.  A result of upright sitting

Screen Shot 2016-06-02 at 14.18.03The backward rotation of the pelvis when sitting pelvic results from the weight of the upper body acting down on it via the spine and has already been described (Biomechanics/Effects on sitting posture) and it’s effect of reducing the IVD wedge angle (Angles & lordosis).  AC Mandal described this change and how a misconceived lumbar backrest, that is intended to reproduce the lordotic curve which pertains while standing, was arrived at in the 1920’s.  It provided the theoretical basis for the adverse traditional ‘correct’ sitting posture. ☛ Why? Mandal’s homo sedans→ . It was reinforced when Cyriax126 pointed out the importance of lordosis in avoiding retropulsion of the disc contents with his adage “Preserve the lumbar curve”.

Position of the back support

This is important.  The effectiveness of any upright chair in reducing LBP depends on it.  Iliac support can be a component of a 2T chair both as a remedial component for the upright mode and also to prevent a backward tilt in the reclined mode.

Screen Shot 2016-06-02 at 14.32.12

Not all authorities agree on the terminology. Above is my own view. HAS.

Screen Shot 2014-02-05 at 11.59.11The height of the posterior superior iliac spine above a seat (ignoring interposed soft tissues] Is between 146 – 168 mm.   (Diag. by Wicketts D, 2014, after Reynolds)

 

 

 

 

Height adjustment?

Most work chairs have adjustment mechanisms that puts the support above 20 cm.  This is to accomodate the tall user.  This mistaken concept should be resisted and adjustments avoided.  If adjusted higher there is a potential to result in adverse effects for average users.. A tall person might lose some mechanical advantage but would not incur any harm. A chair designed for a large person can have the iliac support at a higher level (max 168 mm,) that would be adverse for a small person.

Pelvic and Iliac support.  

Iliac variety Pelvic support was developed by John Gorman an engineer and chiropractor (Gorman’s41) was in contradistinction to existing ‘lumbar support’,  Precise support, shaped to the curve of the iliac crest is  applied to the posterior iliac spine and iliac crest of the pelvis.   A slight forward nudge at this point is mechanically efficient in extending the two lowest joints and prevents the pelvis rotating backwards.This brings the iliac support round to encircle the entire Iliac crest, ie. half way round the lower torso.  This is certainly comfortable and gives maximum mechanical effectiveness.  However chair designers don’t like it as it looks “too like a hospital chair for the disabled”.Screen Shot 2013-09-27 at 17.45.44

 

 Screen Shot 2013-09-29 at 14.29.22A compromise is to direct the support to the posterior superior iliac spine (the back of the iliac crest).  This should be adequate to prevent the pelvis from tilting backwards but may be less comfortable.

Screen Shot 2013-09-29 at 18.33.37Following the publication of Gorman’s ‘Pelvic Posture’ principle a number of other systems have been developed also called ‘pelvic support’.    Subsequent designers seem to have missed this point and allow pressure to be directed  to the L5 & S1 spinous processes in  the mid-line  which gives uncomfortable point pressure.  More correctly, this is ‘sacral support’.   In retrospect it was perhaps unfortunate that Gorman named this concept ‘Pelvic Support’ when more precisely it is Iliac support.    Pelvic support, of some sort, has increasingly become accepted into mainstream chair design. Even cheaper chairs tend to direct the support to the level of the iliac crests although Gorman’s work may not have been recognised and not fully implemented.

 Gorman’s analysis.  He wrote:-

“The theory of lumbar support is a simple mechanical error; the result of orthopaedic surgeons not having engineering knowledge and seat and chair engineers, no anatomical knowledge.


When we sit, the primary effect is the backward rolling of the pelvis, because all the leg muscles connect to the pelvis so, when the thigh goes from vertical to horizontal (or beyond) in sitting, the pelvis tends to roll back too. (Tight clothing accentuates this).  The weight of the upper body transfers down the spine, on to the back of the pelvis – rolling it backwards.  These two effects cannot be resisted by supporting the spine directly, and the result is maximum bending force where the spine connects to the pelvis. This is exactly what lumbar support causes.”        (John Gorman).

His mechanical analysis, showed that, in the sitting position, a support behind the lumbar joints results in flexion of the L5/S1 joint (X). This is the joint at which 80% of disc pathology occurs and flexion is precisely the position that has to be avoided, particularly if the wedge angle can fall below 0° (ie. vertebral joint surfaces parallel), which is usual in Western populations.   Schorberth132 showed that the pelvis rotates by 40° on changing from the standing to sitting mode with lordosis loss at the vulnerable L4/5 & L5/S1 joints.

P v. L Gorman

The Gorman paradox. Support of the lumbar spine at the levels above the pelvis resulting in adverse flexion at the lowest 2 joints seems to be at variance with common experience and is difficult to understand.   The spine is generally conceived as a semi rigid column of chunky bones, equivalent to a  vertical flexible rod, so lumbar support seems reasonable.      However, the anatomical reality is that the lower end of the flexible rod is firmly embedded in a large solid chunk of material, the pelvis.  In this case the force directed at the rod will result in lordosis at its point of application but this changes to a position of flexion at the lowest one or two joints which are fixed to the relatively solid pelvis.

 Gorman’s calculations were unexpectedly and serendipitously confirmed by a study in Sweden, by Andersson (et al129 ) to show the effect of spinal inclination on the lumbar joints in the upright sitting position.   A number of angles (see below) were measured radiographically while standing, and sitting with  various angles of backrest and various depths of lumbar supports at different levels.    Gorman took Andersson’s raw data and re-expressed them as follows:-

Difference, in degrees, of joint flexion/extension at various spinal levels and thickness of lumbar support (-2, 0, +2, +4 cms)

FTS2

 

Gorman’s own account can be seen→

  • Note that at +2  cm of lumbar support, in column 3, in spite of 3.5° of extension at L1, the important L5/S1 joint is pushed into 4.9° of flexion!
  • Also, in row 2, that the +2 cm of lumbar support results in flexion of the L5/S1 joint even when compared to sitting with no support, described by Lueuder as “the worst possible position”.  The L5/S1 joint is only moved into extension when the lumbar support is 4 cm thick.  This amount is uncomfortable.
  •   These points were not commented on by the authors but Gorman asserts that “these figures means that lumbar support is having exactly the opposite effect to that intended.” 
  • More recently this view has been further confirmed by pMRI studies (Smith FE 2006137).
  • pMRI sagittal lumbar scan with lumbar (not pelvic) support

Screen Shot 2013-09-27 at 17.28.28

The upper lumbar joints are in extension and the disc contents are in a central position.

The more relevant lower two discs have reduced wedge angles and there is retropulsion of disc contents at L5/S1 which appear to be about to extrude.

Screen Shot 2013-09-25 at 22.31.53This effect deserves further study.

 

 

 

Gorman wrote:- “If the backrest is flat or only gently curved -seen from above- then it will only contact the sacrum (at 10cm or so above hard surface) or the posterior iliac spines.This could still be pelvic support but much less effective because it is only half the height and therefore half the leverage or mechanical advantage. The 20 cm level at the back will indeed be the lumbar spine.”13         Gorman also wrote (13/3/20013). “One of the problems of making a backrest effective in an upright chair -and this applied to our pelvic support chairs too- is that most of the users don’t sit properly against the backrest. Just look around any office.   The only people sitting up straight with full contact with the backrest are those that already have a back problem !   Everyone else is more or less slumping. “

For Gorman’s view on origins of LBP→

 JD Gorman explains the difference in stresses of posterior elements which occur in Lumbar and Pelvic support.

Henry      See attached pic from my document at Naturaljointmobility. 

Screen Shot 2013-09-29 at 20.03.44

A. If this car seat incorporated Iliac support, then the compressive force in the L5/S disk would be a bit less than the 40kg weight of the whole of the upper body.

B. If a lumbar support seat, as shown, then the only thing that can resist the occurring backward rolling of the pelvis is a tension in the red ‘posterior elements’ thing, the supraspinous ligament, the fascia or muscles. Regardless of the contribution of each of these structures in resisting the backward rolling, their total tension must result in additional compression in the disc.  Very roughly, by simple mechanics, in this drawing, the compression will be an additional  80 kg or so , tripling the compressive force in the spine to 120kg (very rough calculation!!)

Incidentally this shows the agreement between us of preserving lumbar lordosis and against the standard office chair or car seat.   You see the compression in the disc as the problem and I see the tension in the “red” ligaments as the problem because it stretches them outside their natural range.    Regards,   John

Reply (From HAS)

John.      An interesting analysis.  I think we agree that the common pathway to IDD is increased intra-discal pressure and associated with reduction of the disc wedge angle.  Your analysis shows that lumbar support may increase the axial pressure in addition to allowing backward tilting of the pelvis and reduction of the wedge angle.   In popular parlance, a ‘double-whammy’.  This may account for the discrepancies in the findings of intra-discal pressure research where the precise support is not specified ( a vague photograph is inadequate).

In addition to the above you are also postulating malfunction due to ligament stretching and a muscle ‘over centred’ position.   I mention this in the post ‘Anatomy’/ligaments where CTD is mentioned.  Solomonov seems to be the expert here.  Yours,  Henry

Next ☛  The FORWARD TILTED SEAT (FTS).

ISCHIAL OFF LOAD system

A Partial solution.

The Ischial Off Load system consists of a convex chair seat.  This combines both a FTS and allows, at the back half, pelvic support.

The front half of the seat is tilted forward approximating to a FTS so that the upper body static load ‘Off Loads’ pressure from ischial tuberosities to the thighs when sitting forward  and, depending on the chair height, increases the hip angle.   The back half (BPS) tilts back by 18° and allows the torso to sink back against the ‘Lumbar’ support (One hopes that this is pelvic not lumbar support) and so some of the static load transfers from the ischium to the backrest.   The ischial tuberosities get wedged against the backward sloping part of the seat surface which prevents the normal tendency to slide forwards on the seat when the lumbar or pelvic support pushes forwards enough to be effective. This means that the support can be more effective and if low enough can be pelvic support even though it doesn’t come round the sides of the iliac crest as in the original Gorman model which was more comfortable, effective and had no need for adjustment.  This advantage is slight compared to that of a reclined mode.

In the Makhsous study (135),  kinematic, force, EMG, and X-Ray data were collected at the lower lumbar spine and showed some reduction of intra-discal load compared to unsupported or sitting with a straight backrest.  An ‘Off Load’ system seems to be described although the term is not used.   In the design used, adjustments could be made in the back and ischial supports  A plethora of adjustments is confusing and can be adverse, in a work chair, if adjusted wrongly.  Ideally they should be avoided.

‘Off Load’ is perhaps an unfortunate term.   Off loading from the ischial tuberosities (ITs) is subsidiary to the  extension of the hips due to the FTS effect and and pelvic support achieved by the back half of the seat.

I have noticed that users tend to take advantage of the FTS component and perch on the front edge.  It is still possible for the user to sit in the middle of the seat and so adopt the upright ‘worst possible position’.

Gorman, himself, has posted a comment, in his usual vigorous style, related to the backward component.

reply

From JD Gorman     24 August 2013 16:34
Re: ‘Off Loading’.
Reading through the Makhsous document, off loading seems to mean reducing the force supporting the body at the ischial tuberosities which must then be replaced by a force to take the weight on the thighs via the hip joint. Why this should be promoted as advantageous, I cant think. The ischial tuberosities have been the support point in sitting for 50 million years in the monkeys, the apes and all our bipedal ancestors.

I think the authors have misunderstood the mechanics of sitting with the rear part of the seat sloped backwards. On trying a similar chair, the curiously named DROOP SNOOT,  I found that the ischial tuberosities got wedged against the backward sloping part of the seat surface which stops the normal tendency to slide forwards on the seat when the lumbar or pelvic support pushes forwards.    This means that the lumbar support can be very effective and if low enough can be pelvic support even though it doesn’t come round the sides of the iliac crest (as in my original concept).

Those DROOP SNOOT chairs certainly worked for back sufferers in locating the pelvis but the forces were high which made them uncomfortable for prolonged sitting.   They sold in all the back shops about 20 years ago and I visited the manufacturers in High Wycombe.

As you say seats like the HM Aaron chair do the same to some extent but not as much as the solid seat of the droop snoot. If it fixes the pelvis and therefore eliminates the backward rolling then it will eliminate the bending force in the spine which normally stops the backward rolling which occurs with normal lumbar support. This would reduce intra-discal pressure because part of the pressure is the direct axial weight. The other part is due to the tension in ligaments, such as  the supraspinous. ie bending force in the spine will result in compression just as it does in lifting.     John

 

JD Gorman explains the difference in stresses of posterior elements which occur in Lumbar and Pelvic support.

Henry      See attached pic from my document at http://www.naturaljointmobility.info/Prosthetic%20supraspinous%20Ligament.htm

Screen Shot 2013-09-29 at 20.03.44

A. If this car seat incorporated Iliac support, then the compressive force in the L5/S disk would be a bit less than the 40kg weight of the whole of the upper body.

B. If a lumbar support seat, as shown, then the only thing that can resist the occurring backward rolling of the pelvis is a tension in the red ‘posterior elements’ thing, the supraspinous ligament, the fascia or muscles. Regardless of the contribution of each of these structures in resisting the backward rolling, their total tension must result in additional compression in the disc.                  Very roughly, by simple mechanics, in this drawing, the compression will be an additional  80 kg or so , tripling the compressive force in the spine to 120kg (very rough calculation!!)

Incidentally this shows the agreement between us of preserving lumbar lordosis and against the standard office chair or car seat.   You see the compression in the disc as the problem and I see the tension in the “red” ligaments as the problem because it stretches them outside their natural range.    Regards,   John

Reply (From HAS)

John.      An interesting analysis.  I think we agree that the common pathway to IDD is increased intra-discal pressure and associated with reduction of the disc wedge angle due to flexion of the lower lumbar joints.  Your analysis shows that lumbar support may increase the axial pressure in addition to allowing backward tilting of the pelvis and reduction of the wedge angle.   In popular parlance, a ‘double-whammy’.  This may account for the discrepancies in the findings of intra-discal pressure research where the precise support is not specified ( a vague photograph is inadequate).

In addition to the above you are also postulating malfunction due to ligament stretching and a muscle ‘over centred’ position.   I mention this in the post ‘Anatomy’/ligaments where CTD is mentioned.  Solomonov18 seems to be the expert here.  Yours,  Henry

Next ☛  Sit Stand & stools

The 2T CONCEPT

OVERVIEW.   The 2 TILT (or 3M) chair CONCEPT.

The concepts derived from the scientific evidence.  see ☛Biomechanics→ .   It  is the optimised default  against which the ergonomics of any chair can be assessed.    An essential tool for chair designers.

Screen Shot 2015-12-22 at 15.18.35

Screen Shot 2015-10-07 at 13.43.22Two Tilt, 2T,  So called as there are only 2 stable modes, each at either end of range. The unstable transition is also a mode with actual benefits and allows the concept to be renamed Tri-Modal concept (3M).  The addition of a standing mode creates a Quadri-Mode (4M) chair station with a Sit/Stand capability.   The 2T concept, in it’s early days being a paradigm shift, engendered ‘familiarity bias’ for designers.   This is now decreasing  ☛Uptake & implications→

The identified  adverse bio-mechanical factors

Screen Shot 2016-03-13 at 15.11.47

These are described under ☛ Remediation→.  Listed here are those requiring remediation to ensure a safe sitting position :-

  • The intradiscal pressure (IDP) from spinal axial loading in the upright state.  ☛Loading→ Raised IDP has increasing effect with degeneration which occurs in most people and may start surprisingly early.  ☛Inter Vertebral Disc (IVD)→
  • Additional mechanical factors, such as flexion and rotation are required for  disc prolapse to result.
  • A kyphotic, flexed lumbar spinal position leading to stretching of the posterior elements and ☛CDT→.
  • Reduction of the IV Disc wedge angle  (☛Sato 1999).
  • The retroversion (backward tilt or to an an anatomist a ‘forward tilt’)  of the pelvis, which occurs on sitting upright, reduces or reverses the protective disc wedge angle.
  • A hip angle of 90° which occurs with a seat parallel to the floor allowing the hip extensor muscles (hamstring & glutei) to rotate the pelvis so as to flatten the lumbar lordosis. Ideal angle of hip extension is 130° shown by pMRI (☛Smith 2006).
  • A prolonged constrained posture.
  • Sleeplessness. (For an account see ☛Metrojet→ )

Only a reclined posture, basic to the 2Tilt chair concept, can reduce all these and this must be the only logical system for a prolonged working position.   The 2T is the default  against which the ergonomics of any chair can be assessed.    An essential tool for chair designers.

Screen Shot 2016-03-18 at 18.08.46REQUIREMENTS for the 2Tilt concept.

To achieve an efficient working 2T (3M) chair a number of requirements are essential.            

Principle 1

Reclined mode. The optimum for prolonged work

Prolonged sitting tasks should be performed in the reclined position with the backrest at 40-45° Screen Shot 2016-03-16 at 10.44.00from the horizontal using a normal desk. This can be reduced with a desk-less version.   Support is given to the whole length of the body, from head to feet.  pMRI studies  have confirmed that the risk of posterior  disc displacement is avoided by supine or semi-supine positions.(Smith,2006).

In the reclined mode  some requirements are necessary to ensure optimal support and must include the following.

  • Requirement 1 Support is given to the entire length of the body, from head to feet with  a  back support correctly configured to spinal morphology, with iliac support at correct level and shape.
  • Requirement 2. Even with the reduced axial loading the lumbar lordosis should be maintained and this is best effected by some pelvic (not lumbar) support. This should only be sufficient to avoid lumbar flattening, and should avoid excessive lordosis.
  • Requirement 3. Some extra curve (kyphosis) of the thoracic spine, over that which pertains on standing, is allowed because it is fully supported and is a stable area and not liable to mechanical breakdown. It extends, with the upper lumbar joints, over 14 segments and the extra flexion at any single joint is minimal.
  • Requirement 4. A correctly placed head/neck-rest is required so that the occupant has no need to move the neck to establish the task-related visual field.
  • Requirement 5. It is necessary to have support for the legs and feet.  Compression of the calf muscles should be avoided.   A spring exercise system is an advantage.  The floor is allowed as a foot-rest  if the knees can remain extended.
  • Requirement 6.  Variability at head and feet only.   These are the most variable parts of the human body, in the reclined mode.       Adjustments avoided elsewhere.      ☛Adjustments→.
  • A reclined 40-45° position is advised for a stand-alone 2T chair.   Greater angle, nearer fully supine, is possible with a deskless work station  ☛4M OFFICE WORK-STATION→. 
  •  See ☛The 2T reclined mode→

Principle 2. (Hence the 2T concept)

A 2Tilt  Upright Mode  is subsidiary but  required for certain short activities and quitting the chair Screen Shot 2016-03-16 at 10.52.32and is the default mode when the chair is unoccupied.  ☛2T Upright modes→   ☞Mandal

 

• Requirement 7. Maintaining the wedge angle of the lower two lumbar joints, in the upright mode, can be achieved by a ☛forward tilted seat (FTS) or by correct use of ☛ iliac support. The latter cause additional design problems in this case and so is not recommended for an original design but may be convenient for modification of an existing model.

Principle 3.  An unstable transitional mode.

• Requirement 8.    Mid ranges should be unstable and easily negotiated.  It is necessary to be able Screen Shot 2015-10-07 at 13.43.22to switch rapidly and easily from a reclined to the upright mode.

  •  This is mainly for convenience but the switch also results in a change of pressure on the disc and this has the added advantage of providing a pumping action which aids disc nutrition.
  •  No adjustment is allowed to maintain an intermediate position
  • These reproduce the conventional adverse sitting posture and should be avoided. (☛Mandal→)
  • Their instability  can be used for short periods as a form of exercise ( ☛ dynamic seating→),
  • Particularly for rehabilitation of the Multifidus (☛ muscles→) following an internal derangement at the low lumbar joints.      For a fuller account. see ☛Unstable intermediate mode →

 

Principle 4

Requirement  9. Adjustments should be avoided, as far as possible

except for the head and feet and possibly height of seat.  As variation in size of the skeleton of a human torso is not great except for the soft tissues and to the long (limb) bones there is no need for variability to be built into the chair parts that support the torso. With most chairs these are adjusted into the wrong position! This flies in the face of chair designers who are searching for the Holy Grail of infinite adjustability. If a manufacturer prefer a plethora of adjustments, although increasing costs and degrading the green footprint, this does not entirely negate the 2T principles. Although as far as possible, adjustments should be avoided, the footrest position must adjust to leg-length.  (See ☛ Adjustments→)

Principle 5

(Requirement 10) The 4M deskless work station with standing mode.

A stand facility can be incorporated in the desk-less station version.    ☛Sit/Stand→ ☛4M office work station→

 

Next ☛  The 2Tilt RECLINED MODE→

 

 

Sit Stand & stools

A Partial solution.

The Sit Stand concept  has slowed following work showing less difference in sitting and standing intra-discal pressures than was first thought.  A comeback is occurring as the  importance of keeping staff exercised is recognised.   

The Sit Stand concept is ergonomically superior to the use of existing upright chairs and can be an adjunct to the 2T system which then becomes a 4M concept (and a ‘full’ solution).

Screen Shot 2015-12-17 at 18.07.27

Most people prefer sitting, because it is energy efficient with less action by the Erector Spinae muscles than when standing.   However there are situations where the concept is applicable and as the  importance of keeping staff exercised is increasingly recognised.   The negative consequences of constrained sitting has been described by a number of authorities.  See ☛ Exercise & movement→

Ben SchillerThe first known ‘office-based’ study in the Department of Clinical Sciences and Nutrition, at the University of Chester, Chester, UK, 2016,  compared two days of continuous monitored capillary blood glucose responses to sitting and standing in normally desk-based workers.  The results provided encouraging signs of attenuating post-prandial glycaemic excursion  and why avoiding continuous sitting at work could benefit cardio-metabolic health.  The following articles are referenced:-

  1. Stand mode
    Freed from the constraint of a worktop desk, a stand mode can be easily designed using the 4M concept.  This may help staff to move about and relate to others.
    But, on the other hand prologed standing is tiring and affects venous return and can adversely affect body and cognitive abilities. – Are Standing Desks The Biggest Sham Ever?→    Wilmot EG, Edwardson CL, Achana FA, et al. Sedentary time in adults and the association with diabetes, cardiovascular disease and death: systematic review and meta-analysis. Diabetologia 2012;55:2895–905.Screen Shot 2018-03-09 at 16.35.37
  2. Saunders TJ, Larouche R, Colley RC, et al. Acute sedentary behaviour and markers of cardiometabolic risk: a systematic review of intervention studies. J Nutr Metab 2012;2012:712435.
  3. Gennuso KP, Gangnon RE, Matthews CE, et al. Sedentary behavior, physical activity, and markers of health in older adults. Med Sci Sports Exerc 2013;45:1493–500.
  4. Leon-Munoz LM, Martinez-Gomez D, Balboa-Castillo T, et al. Continued sedentariness, change in sitting time, and mortality in older adults. Med Sci Sports Exerc 2013;45:1501–7.
  5.  Levine JA, Schleusner SJ, Jensen MD. Energy expenditure of nonexercise activity. Am J Clin Nutr 2000;72:1451–4.
  6.  Koepp GA, Manohar CU, McCrady-Spitzer SK, et al. Treadmill desks: a 1-year prospective trial. Obesity 2013;21:705–11.
  7.  Peddie MC, Bone JL, Rehrer NJ, et al. Breaking prolonged sitting reduces postprandial glycemia in healthy, normal-weight adults: a randomized crossover trial. Am J Clin Nutr 2013;98:358–66.
  8.  Pescatello LS, Arena R, Riebe D, et al. (Eds). ACSM’s Guidelines for exercise testing and prescription. Baltimore: Lippincott, Williams and Wilkins, 2013.
  9.  Speck RM, Schmitz KH. Energy expenditure comparison: a pilot study of standing instead of sitting at work for obesity prevention. Prev Med 2011;52:283–4.
  10.  Blaak EE, Antoine JM, Benton D, et al. Impact of postprandial glycaemia on health and prevention of disease. Obesity Rev 2012;13:923–84.
  11.  Service FJ. Glucose variability. Diabetes 2013;62:1398–404.
  12.  Satya Krishna SV, Kota SK, Modi KD. Glycemic variability: clinical implications. Indian J Endocrinol Metab 2013;17:611–19.

Effect of movement on the IV disc

It has been shown that disc nutrition depends on the pumping action of pressure changes due to changes of position and is probably important in avoiding later degenerative changes.  In the context of chair design, movement is comforting and avoids the adverse effects of a prolonged constrained static upright mode on general health (See (Lueder R 2002).  

Effect of axial loading  on sitting

Originally Nachemson and others showed that the standing position had a lower intradiscal pressure than upright sitting.  This suggested that incorporating sitting and standing, with a sit/stand desk, could be beneficial if designed into an office environment.

Screen Shot 2015-09-30 at 15.05.52This concept  has slowed following later work (Wilke 1999) showing less difference in sitting and standing intra-discal pressures and the general recent ergonomic improvement of office chairs.     A number of bio-mechanically efficient stools have been produced which usually incorporate a FTS, contouring and sometimes iliac support.

Screen Shot 2015-09-30 at 15.15.20☜ The Pesko ERGO FLEX M 1_1 also incorporates a ‘wobble”.

A recent, more complex example is the Freedman chair in which the 2 halves of the seat can move independently, intending to accommodate spinal irregularity (scoliosis) and pelvic side tilting.  The emphasis is on the FTS concept and movement.☟

freedman-chair

Screen Shot 2017-02-20 at 18.22.18The HiLo
by Box Clever 2016, an innovation agency led by industrial designers Bret Recor and Seth Murray for Knoll  Knoll produce a number of high end task chairs with semi-remediation such as pelvic support but have not yet made the jump into a fully remediated chair.

It seems to be an indoor version of the old ‘Shooting sticks’ that I used to use.  Very sensible. (→ https://www.knoll.com/search-results?searchtext=HiLo&parent=1347382605724 )

 A ‘stand’ mode can  be incorporated into the 2T concept with a 3M ‘desk-less’ workstation.  This extra mode results in the 4M, the first change since the inception of the concept in 1998.   (See ☛workstations→).

The exact converse system is designed to get the user off the stool to make way for another user.   A good example is an expensive designer stool with 4 legs and painted black as used in Mac shops.  Photo on 06-01-2015 at 12.49Being an enthusiastic  Mac user myself, I am only too familiar with these.  They have a round, horizontal seat without conturing which allows point pressure between the ischial tuberosities (ITs) and the hard surface.

Problems may arise for staff & users who have to sit on them for longer periods. The view is of myself but It can be seen repeated in some random shots of staff users.   In the unavoidable, high loaded, upright position, the pelvis tilts backwards due to  the horizontal surface of the stool seat.  This is augmented by leaning forward, but some slight positive effect may occur by taking weight on the arms.

Screen Shot 2015-01-20 at 12.27.40

A light hearted account of 19c office conditions is relevant here.

Next ☛ A FULL SOLUTION

The FORWARD TILTED SEAT (FTS).

A Partial solution.

The forward tilted seat concept preserves lumbar spinal lordosis and allows freedom of movement.

As already described (Mandal, A.C.: “The Seated Man”1987) workers in Scandinavia, 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.  No back rest was necessary and the torso was free to move.   The  unsupported spine may incur slightly greater intra-discal loading probably from muscle co-contraction which is tiring and makes the FTS unpopular.   Makhsous (Makhsous M. 2003), has shown that sitting on a horizontal surface involves lumbar flexion relative to standing and   has also shown that with seat angled down, weight is largely shifted to the proximal half of the thighs at 18°. This was also shown in previous work (Corlett, 1999, Eklund et al, 1982, Schoberth, 1978).  This is not relevant for  it’s short use in a 3M chair.

Screen Shot 2016-06-02 at 13.00.47

Mandal determined, by tilted incrementally the chair seat and work surface, that an optimal position resulted in a correct lumbo-sacral lordosis and hip extension. He concluded “The recommended chair height is one-third of the person’s height, and the desk height one half. Most people with back pain will find this very comfortable, but for the first weeks you will only be able to sit like this for 5-10 minutes, because your back muscles need training.”  ☞ Mandal

Screen Shot 2016-06-02 at 13.16.01

The kneeling component of the Balans chair, shown, is to prevent forward slipping.  With a static FTS this tendency to slide forward is tiring to resist.  Alternative options are non-slip materials, memory foam and configuring for both comfort and ‘butt pockets’ to relieve pressure on the Ischial Tuberosities (ITs). (See 2T Upright mode→)

 The Forward tilted Seat and The Ischial Off Load’ system

The Ischial Off Load’ system is a variant consisting of a convex chair seat so that the  front half of the seat is tilted forward approximating to a FTS.

Next, for details,  see the ☛ Ischial ‘off-load’ system