This work is intended to explore the bio-mechanical factors that may determine spinal pathology that leads to backache (Low Back Pain. LBP) and serious spinal pathology.  Once identified, corrective measures can be developed, which are described.  It is hoped that it will provide a resource for chair designers so that  the common misconceived  views can be avoided.   A fully optimised system is also described.

The present position.  How did we get here?

Mandal 1As long ago as 1985 AC Mandal explained that the upright sitting posture, advocated as ‘correct’ was seriously flawed  (See  ☛ Why? Mandal’s Homo sedens.→).   This has been validated by subsequent research but is still advocated as ‘correct’.  Mandal advocated a forward tilted seat (FTS) which is incorporated into the    Ischial off-load system now used by some high-end office chairs.    (See  ☛ . mid-upright sitting.→).

Early Intra-discal pressure studies suggested that upright sitting pressure was higher than when standing.   This resulted in the adoption of Stand/Sit systems.  Later studies showed little or no difference between sitting and standing pressures.   However the large pressure difference between the standing and a reclined modes were confirmed.

Cyriax JH in the 1940s Suggested that the lumbar flexion on sitting resulted in  backward translation of the inter-vertebral disc (IVD) contents.   To this was added the effect of stretching of the ligaments posterior to the lumbar joints.   Gorman JD, an engineer turned chiropractor, showed how this effect could be remediated by correctly placed back support at the level of the Iliac crest which he called ‘Pelvic Support’ as distinct from ‘Lumbar Support’.   (☛BACKRESTS. Pelvic support v. Lumbar.→).

A reclined position for prolonged work provides the only system that corrects all the adverse effects of conventional prolonged upright sitting. the necessity  was found that included a reclined mode →.   For a reclined office work-chair to be practical a number of requirements are essential including a secondary upright mode for short tasks and an east transition between these two modes.  Designated the 2 Tilt (2T) concept  this has been changed.   2T is now designated 3M (tri-modal) since the health benefits of  the transitional mode, providing it was unstable, were recognised..

These have been covered here in the The 2 TILT CONCEPT→.   A 2T prototype was tested for practicality in the Cambridge University MfI department.    A   Sit/Stand facility can be incorporated to become a 4M version workstation.   ( ☛OFFICE WORK-STATIONS→.).   Although originally considered outlandish in 1998, recently design is at last  moving in this direction.  (☛The FUTURE is GOING THE 2T (4M) WAY→).

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Requirements for optimising the bio-mechanics of prolonged sittingScreen Shot 2018-07-08 at 19.38.22

Partial remediations.

Partial solutionsSystems in use at present,    See ☛ REMEDIATION

The obvious, and perhaps only, solution was for prolonged work to be performed in a chair that has a stable, correctly supported, supine reclined mode. Shown here is the Okamura ‘Atlas’ chair.  ☛ Atlas→

Screen Shot 2013-09-29 at 14.29.22Other, commonly used partial solutions include ☛ Pelvic support→,

 ☛forward tilted seat→, & Ischial off-load →

& ☛Sit/Stand→.

2T direction

The big story here, however, is that it was found that a reclined mode is the only position that avoids all the adverse effects of prolonged upright sitting.    For a reclined office work-chair to be practical a number of requirements are essential.  

Combining these requirements can be difficult to achieve but is possible in a Screen Shot 2018-07-08 at 19.44.36suitably supported reclined mode at 40-45° which conforms to spinal morphology (configuration). This alone is impractical as a work position unless a number of secondary requirements are incorporated to make this simple concept suitable and practical for a work chair.

  1. A  reclined mode which has a correctly supported, supine, stable position  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→     With the recognition that the transition movement has physiological advantages, this has been upgraded to a ‘mode’.   dynamic seating→



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‘Sitting disease’

Compared to people who sit the least, those who spend most time in a chair have a 112 % higher risk of developing diabetes, a 147% higher risk of suffering “cardiovascular events” such as strokes and a 49%t increased risk of death from any cause.  (   Alarming but not entirely an effect of the bio-mechanics and not examined here.  However some posts are relevant.


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