A full size bicycle would be difficult (if not impossible) for a six-year-old child to use, just as a full grown adult would find it difficult and uncomfortable to ride the six-year-old’s bike. But when in the right hands, each machine is ideally suited to its rider – in other words they are both ergonomically appropriate and efficient but user and machine need to be tailored to one another.

In the world of furniture, particularly in the office environment, ergonomic suitability or efficiency is usually measured (if comfort and discomfort can be measured) by how comfortable the furniture item is, and for how long.

In essence HF&E is the study of designing machinery, devices and equipment (in this context, “equipment” includes furniture) that suit the human body they have been designed for. The two terms "human factors" and "ergonomics" are essentially the same thing.

Ergonomics have an important part to play in the fields of occupational health and safety and productivity. If an object is difficult or uncomfortable to use, mistakes could be made leading to mental or physical injury, or excessive strain could be placed on the user, resulting in the same unfortunate outcome.

What makes an ergonomic office chair?

Its design, its suitability to the user, and its adaptability to one or more users. A properly designed office chair will prevent lumbar strain and back pain; when adjusted to the correct height for the user it can also be instrumental in minimising the risk of repetitive strain injury (RSI) by ensuring that computer keyboards are set at the optimum height.

Sitting down is all about moving around.

The human body is designed to move about. On the surface a contradiction, but one of the most important aspects of a good sitting habit is movement. Getting up from your chair and frequently adjusting your sitting posture is one of the best methods of preventing injury and tiredness. The best chair design in the world will not guarantee good posture or eliminate the need for the human body to move about.

If you’re not in the furniture business this might be a new term to you: seat pan. The “pan” of a chair is the flattish bit that you sit on.

You may not have previously given a lot of thought to how to choose something as mundane as a chair, but if you spend a lot of time sitting down your choice of chair can significantly impact on your quality of life, not just today and this week but also for a long time into the future.

And if you are an employer, providing the wrong kind of chair for your employees might have serious consequences.

Questions to ask:

Does the seat pan feel comfortable and fit your shape?

The seat pan should not be too long for your thighs; otherwise, it will either catch behind the knees or prevent you from leaning fully back against the lumbar support. Most ergonomic chairs have a seat pan with a waterfall front - one that curves down and prevents the seat from catching you behind the knees.

Ideally, you should have at least a half-inch gap between the front edge of the seat pan and the back of your knees. The seat pan should be long enough to provide comfortable support for at least three-quarters of the length of your thighs.

The seat pan should also be shaped to allow even weight distribution, and the edge should be soft and contoured. The rear of the seat pan should provide comfortable support. You may also want to choose a chair that swivels easily. 

Is the seat height adjustable?

It is best that the chair should be pneumatically (gas) adjustable so that you can adjust the seat pan height while you are sitting on the chair. Some chairs have a mechanical height adjustment (spinning) mechanism that is not so convenient to use.

Does the range of height adjustment of the chair meet the needs of all users?

You should be able to adjust the height of the seat pan so that the front of your knees is level or slightly below level when your feet are firmly on the ground. In most situations there should be no need for you to use a footrest. The mechanism to adjust the seat height should be easy to reach and operate when you are sitting down.

Does the chair have comfortable lumbar (lower back) support?

Some chairs have cushioned lumbar supports that can be adjusted up and down, and which sometimes adjusts forwards and backwards as well. If a number of people are going to use the chair then this type of adjustment may be required.

Is the chair backrest large enough to provide good back support?

A lot of chairs have back supports that are large enough to provide mid-back and upper-back support right up to shoulder-blade level, as well as good lumbar support. The back of the chair should not prevent you from moving your elbows backwards behind your body.

When you sit back against the lumbar support is there ample space for your hips?

Insufficient hip room can make you sit too far forwards on the seat pan, which means that you will not have enough thigh support. The seat pan should be at least one inch wider than your hips and thighs on either side. 

Does the seat pan still feel comfortable after at least 2 hours?

The use of low-density foam in a seat pan can result in it being permanently deformed, so that it no longer provides adequate cushioned support. This may cause hip and back strain, tiredness and general discomfort. If you possibly can, you should try out a chair you are going to use for long periods for at least a couple of days.

Does backrest recline and support your back in different positions?

Moving your back when sitting helps to maintain a healthy spine. Try to find a chair that allows you to easily recline, and that provides you with good back support in different recline postures. Locking the chair backrest in one position is not recommended because it restricts movement.

Does the chair have a five-pedestal base?

If your chair will need to be moved around at work then the chair should have at least a five-pedestal base; it should have with casters that glide freely over the floor surface. Chairs with five or more casters are more stable than those with only four.

Do you need armrests on your chair?

Most ergonomic chairs have armrests, and where they do, they should be adjustable. The armrests should be designed to be broad, contoured, cushioned, and comfortable.

Other Considerations

Do you need a footrest?

In most situations you should not need a foot support in order to sit comfortably on your chair. However, if you do need a foot support, choose a free-standing, floor-mounted support that allows you to rest your feet out in front of you comfortably. Resting your feet on the pedestal base of your chair is not a good idea for prolonged periods because the knee angle will be less than 90 degrees, when some restriction of blood circulation could occur.

What chair covering is best?

Chairs can be covered in a variety of upholstery materials, each of which has pros and cons. Vinyl and vinyl-like coverings are spill resistant and easy to clean, but they can’t breathe, so if the chair begins to heat up under your thighs, you’re likely to feel hot and sticky.

Cloth upholstery is the most poplar chair covering, but this is less resistant to spills and harder to clean. A cloth-covered seat pan can also become warm and moisture-laden. There is also some evidence that cloth-covered foam seat pans can be a source of dust-mite allergen. When choosing your chair covering, think about cleaning and maintenance.

Do you need an adjustable-tilt seat pan?

Not usually, but in some situations it can be helpful to change the tilt of the seat pan to help to maintain a balanced posture.

The belt and braces approach

If you really want to fine-tune your work station to suit you then consider the advantages of a sit-stand adjustable desk as well. Powered by a small electric motor, such desks will allow you to adopt a range of postures throughout the working day to minimise strain. After all, the body is designed for moving about.