Why support does not automatically change posture
An ergonomic chair can make sitting more comfortable by supporting parts of the body, but it cannot position you at the desk or keep you from leaning forward. If the screen or keyboard feels too far away, your body may move toward it anyway. The chair remains behind you while your head and torso shift ahead of its support.
The extra work of leaning
Your head and upper body have weight. When you lean forward, their weight acts farther from the joints and muscles that hold you upright, increasing the effort needed to keep that position. The muscles in your neck, back, and trunk must continue producing force; a chair’s backrest cannot take that load if you are no longer leaning against it.
This is why a chair may feel supportive when you sit back but seem to make little difference during focused work. It supports a position; it does not guide your movements or prevent a posture that puts more demand on your muscles.
Change the reach, not just the chair
If you repeatedly lean toward the screen, the setup may be asking you to reach. Bringing the screen closer, placing the keyboard within easy reach, or adjusting the work surface can reduce that pull. The useful test is not whether the chair looks supportive, but whether you can see and type comfortably while using its support.
A good chair can make a supported posture easier to maintain. It cannot support the parts of you that you have moved out in front of it.
