Working at a desk, like eating, is usually a forward activity. A work or dining chair with a backward sloping seat that takes you backward will force you to hunch forward in a strained posture.

The best work chairs allow the seat to be angled slightly forward so that the back of the seat pan is 2-3 inches higher than the front. Ideally this is independent of the seat height and backrest adjustments. There are also wedge shaped cushions easily available which can be used to improve chairs, or car seats.

You also need to consider the height of the seat relative to the floor and the work surface. The feet should be on the floor and the knees no higher than the hips. The backrest needs to be as high as the lower shoulder blades and not angled back very much.

There are many untraditional work chairs available. They all have their fans and are useful for at least some people some of the time.

There are office chairs that rock with the users' movement to allow dynamic sitting. The theory is that this improves circulation, stops stiffening, and reduces strain. Whether one prefers a fixed or moving chair is a matter of personal choice.

The kneeling chair is useful for some people for limited periods of time, but the rather extreme angle of tilt and the pressure on the knees make them unsuitable except for short periods of one or two hours a day.

The saddle stool is shaped like a saddle. It allows the knees to be considerably lower than the hips and is good for people who find it difficult not to slump.

Lumbar support was thought to be absolutely necessary, but it is now recognised that too large a lumbar support or one in the wrong place does more harm than good. People come in such a wide variety of shapes and sizes that a seat with very definite curves built into it will not suit many people. Some people need lumbar support because of weakness in that area of their spine. But be wary of a seat which forces the spine into an exaggerated lordosis or forward curve. See the man on the right in picture number 4 in What to look for in a chair.

The car seat is a work seat but most are angled down at the back. Many people then compound the problem by winding the backrest further back. The driver then hunches the neck and upper body forward creating a very strained position. Some car seats are too soft. Many have curves built into them which force every body into the same shape regardless of individual differences. Better is a more neutral seat of flat planes, soft but firm.

See useful addresses and links for examples

No chair will automatically give you good posture - but some will make it easier, and some will make it impossible.