Office chair synchronous mechanism: The gold standard for dynamic, healthy sitting
The synchronous mechanism links the tilt of the seat and backrest in a fixed ratio, typically around 1:2 to 1:3 – so if the backrest reclines by a certain angle, the seat follows with only a fraction of that movement. This principle enables dynamic sitting with constant micro-movements and is therefore considered the gold standard for ergonomic office work.
Hardly any term appears as frequently in office chair product descriptions as "synchronous mechanism" – yet what exactly it means and why it clearly outperforms simpler mechanisms often remains unclear. Here is the full technical and ergonomic classification.
How does the synchronous mechanism work in an office chair? The principle explained simply
The linked tilt ratio
With a synchronous mechanism, the seat and backrest do not move independently of each other, but in a fixed, coordinated ratio – typically around 1:2 to 1:3. For example, if the backrest reclines by 30 degrees, the seat simultaneously tilts by only about 10 to 15 degrees. This coordinated ratio ensures that the body remains properly supported in every sitting position instead of abruptly tipping into an unnatural posture.
The "shirt-pull effect" (sliding effect)
With simpler mechanisms, where only the backrest moves independently, a noticeable friction effect between the back and the backrest occurs when leaning back – your shirt or blouse is literally pushed upwards while contact with the lumbar support shifts at the same time. The synchronous mechanism largely prevents this effect, as the contact point between the back and the backrest hardly changes thanks to the linked seat movement.
Individual weight adjustment
So that the counterpressure of the backrest when leaning back matches your body weight, the synchronous mechanism features a spring tension adjustment. This ensures that lighter users do not feel too much resistance and heavier users do not tip backwards uncontrollably.
Synchronous mechanism vs. tilt mechanism vs. permanent contact: The big mechanism comparison
1. Synchronous mechanism
The ergonomic standard for a full office working day: linked movement of seat and backrest, individually adjustable resistance, designed for 8-hour use and more.
2. Tilt mechanism / knee-tilt mechanism
Here, the entire chair including the seat tilts around a shared pivot point, usually in the area of the knee joint. Simpler in design, often used in executive chairs – well suited to short reclining phases, but less suitable for permanently dynamic sitting.
3. Permanent contact mechanism (PKM)
With this mechanism, the seat remains fixed in position while only the backrest moves. This means the back stays in continuous contact with the backrest, but the lack of seat movement limits dynamic sitting compared to the synchronous mechanism.
| Mechanism type | Operating principle | Maximum recommended sitting time | Ergonomic value | Who is it suitable for? |
|---|---|---|---|---|
| Synchronous mechanism | Coordinated tilt of seat and backrest (approx. 1:2 to 1:3) | 8+ hours | Very high | Full-time office work, long-term home office use |
| Tilt mechanism / knee-tilt mechanism | The entire chair tilts around a shared pivot point | Up to approx. 4–6 hours | Medium | Executive chairs, reception areas, short reclining phases |
| Permanent contact mechanism (PKM) | Fixed seat, movable backrest | Up to approx. 6 hours | Medium to good | Occasional users, basic office workstations |
Ergonomic benefits: Why the synchronous mechanism protects the spine & intervertebral discs
Encourages dynamic sitting
The synchronous mechanism allows a continuous change between different sitting positions – from an upright "front wheel position" to a neutral middle position and finally to a relaxed "rear wheel position" when reclining. This constant movement keeps the back muscles active instead of allowing them to slacken in a rigid posture.
Nutrient supply for the intervertebral discs
Intervertebral discs receive nutrients through a passive process called diffusion, which only works when loading and unloading alternate. The constant micro-movements of the synchronous mechanism actively support this exchange, which would be significantly restricted when sitting rigidly without movement.
Support for the lumbar region in every position
Because the seat and backrest move in coordination, contact with the lumbar support is maintained even when reclining – so support for the lower back is not lost as soon as you move out of an upright posture.
Instructions: How to adjust the synchronous mechanism on your office chair correctly
Step 1 – Adjust resistance to your body weight: Lean back to test it – the chair should neither tip backwards uncontrollably nor noticeably push your back forwards. Adjust the spring tension accordingly until you feel a balanced counterpressure.
Step 2 – Activate the free-float function of the mechanism: Release any lock that may be engaged so the mechanism can move freely during the working day – only then will you benefit from dynamic sitting.
Step 3 – Adjust seat depth and seat height: Set both so that your knees and hips form a relaxed angle and your feet rest fully on the floor – only then will the synchronous mechanism deliver its full effect.
Conclusion & buying guide: When is an office chair with a synchronous mechanism indispensable?
For anyone who spends several hours a day at their desk, a synchronous mechanism is not optional but the basic technical requirement for healthy, dynamic sitting. Simpler mechanisms such as a tilt mechanism or permanent contact mechanism may be sufficient for shorter sitting periods or representative areas, but they do not meet the demands of a full working day in the office.
In the range at hjh-office.co.uk, you’ll find high-quality ergonomic office chairs with precisely adjustable synchronous mechanisms – for dynamic sitting that noticeably relieves the strain on your spine and intervertebral discs.