Abstract: Inflatable or inflated seat cushion intended as a training or helping device mainly for sitting upright without a back rest providing as in walking for extensive free play of movement especially in the region of the pelvis and the lumbar, which activates the erecting muscular system and avoids permanent stress. The seat cushion is made of flexible material of several adjacently-arranged communicating chambers which are divided by a groove, whereby the height of the chambers decreases from the back towards the front.