The Office Chair Feature Nobody Explains Properly - Synchro vs Asynchro

When choosing an office chair, we tend to compare the obvious features. Does it have a headrest? Is the backrest mesh or fabric? Are the armrests adjustable?

However, there is another feature which is arguably much more important and rarely explained properly: the mechanism underneath the seat.

The mechanism controls how the seat and backrest move. It has a considerable influence on how the chair feels, how you sit in it and whether it encourages movement or holds you in a more fixed working position.

Two of the terms you will frequently come across are synchronous and asynchronous. They sound technical, but the difference is relatively simple once you see the chairs in action.

Prefer to watch instead? In the Sit School video below, I demonstrate both mechanisms and explain which type of office chair may suit you best.

What does an office chair mechanism do?

The mechanism is normally positioned directly beneath the seat. Depending on the chair, it may be operated using larger levers underneath the seat or smaller controls mounted on either side.

These levers commonly control features such as:

• The height of the chair
• The angle of the backrest
• The angle of the seat
• The seat slide
• The recline movement
• The resistance of the recline

Some of these adjustments may only need to be set once. Others can be used regularly throughout the working day, particularly if you like to change position or move between different tasks.

The key difference between a synchronous and asynchronous chair is how the seat and backrest behave once you sit down.

What is a synchronous office chair mechanism?

A synchronous, or synchro, mechanism allows the seat and backrest to move together as you recline.

They do not normally move through the same distance. The backrest travels through a greater angle while the seat tilts by a smaller amount. This coordinated ratio helps the chair support your body as you move from an upright working position into a more relaxed position.

Depending on the chair, the mechanism can usually be locked upright, locked at different points within the recline or left unlocked so that it moves freely with you.

When the chair is left unlocked, you can move backwards and forwards while remaining supported by the backrest. This introduces some movement through the pelvis and lower back rather than holding you in one completely static posture.

Adjusting the recline resistance

Most good synchronous chairs allow you to adjust how much force is required to recline.

This is often controlled by turning a lever or tension adjustment underneath the seat. Increasing the tension gives the backrest more resistance, while reducing it allows the chair to recline more easily.

Getting this setting right is important. If the resistance is too low, the chair may shoot backwards as soon as you lean against it. If it is too high, you may have to push hard to make the mechanism move at all.

Ideally, the chair should feel balanced beneath you. It should support your weight without forcing you forwards or making you feel as though you are falling backwards.

What are the benefits of a synchro chair?

The main benefit is movement. A synchro mechanism allows you to sit upright when you need to concentrate, but also gives you the freedom to recline when you are reading, attending an online meeting or taking a short break.

From a chiropractor’s perspective, I generally like mechanisms which allow some movement through the lumbar spine and pelvis. Remaining in one rigid position for several hours is rarely comfortable, even if that position looked perfect when you first sat down.

A synchro mechanism does not replace getting up, walking around or exercising. However, it can add some useful movement while you are sitting.

A synchronous chair may suit you if you:

• Like to change position regularly
• Frequently recline while reading or thinking
• Move between focused work and online meetings
• Prefer a chair which responds to your movement
• Become stiff when sitting in one position

Why do some people dislike synchronous movement?

Not everyone likes the feeling of a chair moving underneath them.

I have met people who describe the movement as unsettling or say that they do not completely trust the recline. Some people even feel slightly seasick when first using a chair with a free-moving mechanism.

A well-made chair should remain stable as it reclines, but the sensation still takes some getting used to. It is particularly noticeable if the resistance has not been adjusted correctly for your weight.

Some people buy a synchro chair and immediately lock it upright. They then leave it in that position permanently because they prefer the stability.

There is nothing necessarily wrong with doing that. However, if you know that you dislike reclining movement and will never use it, you may be better suited to an asynchronous chair which offers more precise control over a fixed working position.

What is an asynchronous office chair mechanism?

An asynchronous, or asynchro, mechanism allows the seat and backrest angles to be adjusted independently.

It is sometimes described as a fixed mechanism, although that is not completely accurate. The chair is adjustable, but instead of the seat and backrest moving together automatically, you position each part separately and then lock it where you want it.

For example, you may be able to:

• Change the angle of the backrest
• Tilt the seat forwards or backwards
• Adjust the angle between your hips and trunk
• Move the seat forwards or backwards
• Change the height of the backrest
• Position the lumbar support

Once you have found a comfortable combination, the chair remains in that position. It does not automatically recline as you lean backwards.

What are the benefits of an asynchro chair?

The main advantage is control. An asynchronous mechanism allows you to create a very specific sitting position and leave the chair set up that way.

You may prefer this if you want the backrest to remain firmly behind you without moving every time you change the pressure against it.

Asynchro mechanisms are often found on more traditional ergonomic task chairs. These chairs can be particularly effective when they are being fitted to one regular user.

You can adjust the seat depth, backrest angle, lumbar position, seat angle and armrests around that individual. Once everything feels right, there may be little reason to alter it again.

An asynchronous chair may suit you if you:

• Prefer a stable and predictable sitting position
• Dislike the feeling of a reclining chair
• Want precise control over the seat and backrest angles
• Use the chair mainly for focused desk work
• Want the chair fitted to one regular user
• Do not tend to recline while working

Does an asynchronous chair prevent movement?

An asynchronous chair does not prevent you from moving your body, but it does not actively introduce movement in the same way as a free-moving synchro mechanism.

Once the chair has been adjusted and locked, it remains in that position. You will therefore need to create movement in other ways, such as changing your sitting position, standing up regularly, walking around or doing some simple desk exercises.

That is not necessarily a disadvantage. Some people work better when their chair provides a consistent and supportive base. Others become uncomfortable if they cannot recline and move throughout the day.

The mechanism needs to match the person rather than simply being labelled as better or more ergonomic.

Synchro vs asynchro: the main differences

Which office chair mechanism is best for back pain?

It is tempting to assume that one mechanism must be better for back pain, but it is not quite that simple.

If you become stiff from sitting and enjoy changing position, a synchro mechanism may help by allowing regular movement through your lower back and pelvis.

If your back feels sensitive and you want the reassurance of a firm, supportive position, you may prefer an asynchronous chair which has been carefully adjusted around you.

Back pain alone should not decide which mechanism you choose. You also need to consider how you work, how much you move, whether you like to recline and whether other people will use the chair.

Neither mechanism will provide a magic solution to back pain. A good chair can support you and make sitting more comfortable, but it cannot replace regular movement, appropriate exercise or professional advice when you have an ongoing problem.

What about hot-desking and shared office chairs?

A synchronous chair can often be easier in a hot-desking environment because the user can adjust the height, set the recline resistance and allow the mechanism to move naturally.

An asynchronous chair can offer more precise adjustment, but this also means there are more settings for each new user to change. If someone does not understand what the levers control, they may end up sitting in a chair which was configured for the previous person.

This is something I regularly see during workstation assessments. People may have a highly adjustable chair but only know how to change its height.

Whichever mechanism you choose, it is important that the user understands how it works. An advanced mechanism provides very little benefit if it is never adjusted or used properly.

Which should you choose?

There is no automatic winner between synchronous and asynchronous mechanisms. They are simply different ways of controlling how an office chair supports you.

Choose a synchronous chair if you want a responsive chair which moves with you and allows you to recline throughout the day.

Choose an asynchronous chair if you prefer to create a precise working position, lock the adjustments and leave the chair set up specifically for you.

The important question is not which mechanism sounds more advanced. It is whether you want a chair that moves with you or a chair that stays where you set it.

Final thoughts

The mechanism may not be the most exciting feature to compare when shopping for an office chair, but it can completely change how the chair feels in daily use.

The next time you look at a chair online or try one in person, check whether it uses a synchronous or asynchronous mechanism. Sit in it, operate the controls and see how the movement feels rather than choosing purely from a list of technical specifications.

The best office chair is not necessarily the one with the most adjustments. It is the one which fits your body, supports the way you work and has features you will genuinely use.

Need help choosing an office chair?

At Well Adjusted Seating, we provide chiropractor-led office chair advice, personalised chair fittings and a carefully selected range of ergonomic office chairs.

You can also explore more practical seating advice, buying guides and independent chair reviews through Sit School.