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. It is hoped that it will provide a resource for chair designers so that misconceived views can be avoided.
Why did I bother? As a consultant in Orthopaedic (Musculo-skeletal) Medicine, patients with backache kept asking me to recommend a work chair. A difficult question to answer as there seemed to be no work chair on the market that would do anything other than make prolonged sitting a recipe for making their backache worse. Most users, with even minor degrees of low lumbar backache, the clinicians who treat them and chair designers who aim to help are aware that prolonged sitting is a major factor in aggravating and perpetuating their symptoms.
A renewed look at the pathology and biomechanics related to mechanical Low Back Pain (LBP, Backache) suggested a logical alternative complete solution which is proposed here. (The 2Tilt concept→). At first sight, it may seem odd that the office worker of the near future will be lying in work chairs in a reclined position for some, or most, of the time while using a computer. This is likely to become universal if vindicated by field trials.
Evolution of the 2Tilt concept for sitting safely.
This work, I hope, shows the evolution of thinking from early to later work in relation to sitting and chair design, commonly designated ‘ergonomics’. Patient input and clinical observation is dismissed by scientists as ‘merely’ anecdotal’. However, with several decades of seeing patients with backache, I make no excuse for including some as it is the start of the scientific process which proceeds to systematic analysis, experimentation and efforts towards falsification.
So after 50 years, I decided to look afresh at the basic scientific facts of spinal pathology and bio-mechanicsand see what emerged.
What emerged confirmed the view of the adverse effect of mid-upright sitting of AC Mandal (☛Mandal→ ) and suggested a logical alternative complete solution which is proposed here. ☛ (The 2Tilt concept→), This was a new approach to chair design aimed to address the adverse bio-mechanic problems of the upright sitting mode used in most modern office and work chairs. This was my view advanced in 1998 ☛ Early 2T concept→.
It was met with derision and blank incomprehension! and deemed to be somewhat weird, At first sight, it seemed odd that the office worker of the near future would be lying in work chairs in a reclined position for some, or most, of the time while using a computer. In the next 17 years I have noticed a softening of this incomprehension and an adoption of at least some new ideas. Now (2016), some 16 years later, chairs with a reclined work mode are begining to appear in the market. An example is the Altmark,(☛Some chairs→ ) that has at least an upright and reclined work position. Unfortunately it does not seem entirely 2T compliant. See ☛WORKCHAIRS, a new breed with a reclined mode→.
The 2Tilt concept has remained unaltered except for recognition that the unstable transition mode carried a number of physiological advantages and could be considered as a mode in it’s own right, making the concept Trimodal (3M). The desk-less workstation version, allowing a ‘standing’ mode became a 4 mode concept (4M). ☛work station→ .
A quick overview
For the adverse effects that need to be avoided……
Consider the effects of mid-upright sitting compared to standing
These include permanent stretching of the posterior spinal elements and retropulsion of the disc contents. The latter has been confirmed by pMRI scans (Smith F, 2007→) which show that when sitting upright, the disc contents shift backwards towards pain sensitive structures that can account for common mechanical LBP and can also lead to serious spinal pathology.
The 2 Tilt concept (Also the 3M & 4M concepts)
The bio-mechanical imperatives show that a correctly supported reclined posture addresses the recognised adverse effects and should reduce the incidence of Low Back Pain (LBP) experienced on prolonged sitting. it also ensures maximisation of ‘comfort’. This technical ‘fix’ is required if the increase in personal morbidity, loss of earnings and the huge cost to industry and insurance due to absenteeism and stress due to LBP, is to be halted. The suitability of any chair can be judged (for sitting safely against it (The ☛ complete solution→) . Final scientific evaluation can only be fully validated when models are assessed by controlled field trials against top end existing chairs.
Navigation for Sittingsafely.
The Layout Arrangement of this work.
The menu on the right→ indicates the layout. By simply clicking on the ‘Next’ icon near the bottom of the page it is possible to read this as a booklet. Specialist will prefer to jump directly to their page of interest using the menus.
- Anatomy which includes a number of detailed studies of the more relevant component parts and an account of the paleoanthropology which resulted in the vulnerability of the lumbo-sacral junction.
- Biomechanics in relation to sitting postures.
- The way we sit now, further explores present sitting including the comments (Why? Mandal explains…→), Gorman and others. Comparisons are made with various existing chairs (How do they measure up?→).
- Remediation describes measures that have been taken to improve the ergonomics and their further evolution (2T concept→). Specifically for the general reader are :- Making the best of an upright chair→ & For users & patients only→.
- Also included are Adjustments, comfort, exercise and movement. The way things are going. Special needs, the desk less office chair, pods, school desks & chairs (See menu →).
- The office environment, it’s relation to physiological and psycho-social stress, ergonomics and remediation, the deskless chair and desk/chair interface.
The final posts are intended for developers & manufacturers and include points on impact implications and uptake.
Conclusion. Remediation objectives
Requirements for optimising the bio-mechanics of prolonged sitting
- Reduction of axial loading (Disc compression) →
- Preserve the lumbar lordosis →
- Avoid backward tilting of the pelvis →
- Ensure disc nutrition by pressure changes with movement →
Systems in use at present, partial remediation. See ☛ Remediation→
- Pelvic support →
- Forward tilted seat →
- Ischial off-load →
- Reclined work mode (Okamura) →
- Dynamic seating→
A full remediation, the 2Tilt Concept, is suggested. See ☛ 2T concept→
Combining these requirements can be difficult to achieve but is possible in a suitably 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.