Last week, we focused on the office desk. This week, it is the office chair.

Statistics show an average office worker spends 50 to 90 per cent of working hours in a chair — the reason behind the thrust being given to scientific studies of seating design.

It is essential that office seating is comfortable, appropriate to the task being undertaken and easy for the operator to adjust. The conventional view is people maintain a fixed posture for long periods. But when performing a range of activities, people tend to adopt different postures while seated — and this is desirable, too.

Adjustable chairs

• A chair should be adjustable to the task and be easily adjusted from the seated position

• The seat should be height-adjustable, preferably using a gas lift

• The seat should have a curved front edge to minimise pressure on the underside of the thighs

• It should have a supportive backrest that is adjustable in height, angle and depth.

• The seat and backrest should be covered by a material that breathes.

Stability

The chair should have good stability. While the revolving chair should have a five-star base, the traditional four-legged one must have the legs at least as far apart as the width and depth of the seat above.

Readymade chairs are designed to fit 90-95 per cent of adults. People outside the average range of body measurements should be provided with seating tailored to their needs.

Seat height

Seat height should be set so that the thighs are approximately horizontal and the feet can rest comfortably on the floor. Chairs with adjustable seat heights (not very expensive) should allow adjustments between 15 and 20 inches.

Combine chair and desk adjustments to position the work at elbow height. It is important to note that the height of the work seat must be considered in conjunction with its work table.

The vertical distance from the top level of the seat to the tabletop should be between 11 and 12 inches to provide for proper elbow support when the arms are on the table. If the thighs are wedged between the chair and the under surface of the desk, or the knees bump into the front of the desk, either the desk is too low, the chair is too high, the desk top or keyboard are too thick or the user is too tall for the chair and desk. Request your interior designer to check the ergonomics.

Backrests

Traditionally, offices go for low-height backrests for clerical staff, medium-height ones for senior officers and “thrones” for the bosses. If such “chair hierarchy” can be dispensed with, a scientific backrest that is 22 to 24 inches vertically above its point of contact with the seat is ideal for all.

A backrest that can be tilted backwards from 0 to 7 degrees is best. A tilt more than that is a no-no as it will raise the feet off the floor.

Footrests

This will depend on whether the desk is at the required height once you have adjusted your chair to suit your needs. If the desk is too high and cannot be lowered, raise the chair height and use a footrest to raise the height of the floor by the same amount. Footrests should have height and be large enough to permit some movement while supporting the feet. But a footrest should not be so large that it clashes with the chair base.

Armrests

These are optional. While they help decrease the forces on the shoulders and the back, they can also limit access to the desk. Those who perform a variety of tasks, move frequently to and from the chair or sit back to talk to visitors can go for armrests. However, avoid them if your work involves keying-in as the elbows may rest on the armrests and cause the shoulders to be raised into an unnatural posture.

There is a clear divide. While some workers insist on armrests, others avoid them as they prefer to rest forearms on the table in front. Anyway, remember it is preferable that the armrests be height adjustable.

Alternative seating

Some special forms of alternative seating are available these days to enable people to sit upright with the hips at an angle that is believed to reduce pressure on the lower back. These are usually chosen by personal preference, for example, by someone with lower back pain. Examples include the ‘kneeling’ chair, the ‘sit-stand’ chair or ‘saddle’ chair, and the ‘physio’ or ‘sit’ ball chair.

Although healthy for the spine and back, there are limitations in using these chairs, such as fixedness of the seat angle, awkwardness in getting on and off the seat and low degree of flexibility in reaching, bending and twisting.

Also, there are no firm guidelines or design standards for such alternative chairs. So, go for these if you have a real bad back and do not sit for long periods.

(The author is an interior design consultant, specialising in the design of corporate and residential interiors. As a senior faculty member at a Calcutta institute, she has delivered lectures, guided research and conducted projects in the field of ‘Housing & Interior Design’ for over two decades.

She can be contacted at kusumsmail@yahoo.com )