The 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.
This 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→
- Retroversion (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→
- A 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→
Check back and review ☛ BIOMECHANICS←
Next consider the Requirements for REMEDIATION & optimisation.
- ☛ Reduction of axial loading→
- ☛ Maintain lordosis at the lumbo-sacral junction→
- ☛ Avoid backward tilting of the pelvis→
- ☛ Ensure disc nutrition by pressure changes with movement→
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→
- 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.
- Back support of some sort. ☛ Lumbar v Iliac support→
- 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.
Sit/Stand. For more detail See ☛Sit/Stand→
The negative consequences of constrained sitting has been described by a number of authorities (Adams and Hutton, 1983; Duncan and Ferguson, 1974; Edlund, 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→
There 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.
- A reclined mode for prolonged work ☛2T reclined mode→
- An upright mode required for certain jobs. ☛2T Upright mode→
- 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→