Knowledge Base → Questions → Should a seat be stable or mobile?
Should a seat be stable or mobile?
Neither fixed contact points nor instability: a stable seat that offers constant balance. The body keeps adjusting its posture; a fixed seat blocks these adjustments, and an unstable seat forces the muscles to contract to avoid tipping over. The balance you are looking for lets the pelvis move a little, without the whole seat losing its balance.
What is the difference between fixed, balanced and unstable?
| Fixed contact points (foam, rigid block) | Constant balance | Unstable (ball, inflatable cushion) |
|---|---|---|
| Contact points stay put | Contact points follow the pelvis | Tilting that is hard to control |
| Pelvis held still | Pelvis supported and free to make small movements | Constant effort to stay steady |
| Pressure stays in the same place | Pressure shifts | Fatigue, tensing |
| Comfortable at first, painful later | Tolerable over time | Muscle tension |
Why does this matter with pelvic pain?
Because the effort of holding yourself up sustains contraction of the pelvic muscles. In the pudendal neuralgia cases we have personally assessed, pelvic floor hypertonia has been a consistent clinical observation; a seat that does not force you to hold yourself up spares you the effort that sustains it. The body adjusts its posture from the pelvis to the head (Hasegawa and Dubousset, 2022): a balance that leaves it this margin reduces the effort needed to stay upright.
What is the difference between an inflatable cushion and a balanced dynamic seat on independent supports?
An inflatable cushion moves because it is unstable: your body has to steady it. A balanced dynamic seat on independent supports keeps its balance while its contact points follow the body. Aporia belongs to this second family: its curved base allows an overall rocking motion in all directions. Mounted on this base, four independent pads follow this overall motion; each one also has its own mobility in all directions on an elastomer joint, with a limited range, and supports and follows one of the four body segments in contact with the seat (the two buttocks and the back of the two thighs). The pelvis follows both the overall rocking and the tilt of each pad; each segment follows its pad. To choose: selection guide.
How can you tell a seat is too mobile?
If you tense your legs, pelvis or abdomen to stay steady, or if you tire quickly. A seat that is too fixed shows the opposite signs: pain builds up over time and you keep shifting position.
What other questions do people ask?
Does a dynamic seat keep you moving all the time? No: it lets you move when your body needs to.
Is it right for everyone? No: some situations call for maximum stability; trying it is what shows it.
Publisher: Blue Portance. Written by Gil Ayache, PhD (Mines Paris – PSL). Reviewed: October 19, 2026. Sources: Hasegawa K., Dubousset J., Spine Surgery and Related Research, 2022; Blue Portance page “Continuous postural regulation: the cone of balance”. Aporia® cushions are not medical devices.
Note: this content explains mechanisms related to sitting. It is not a medical diagnosis or prescription, and it does not replace the advice of a healthcare professional.
