A system comprising: at least one platform (13, 53, 13) configured for, in use, having a person on it, said platform (13, 53, 13) comprising a plurality of sensors configured for capturing information of forces/pressures applied by the feet of the person or of the position of the persons feet means for, from said captured information, respectively extracting (65, 65) either a center of pressure or the position of the feet at least one reference signal disposed at a known location with respect to said platform (13, 53, 13) at least one sensor which, in use, is connected to the body of the person situated on said platform (13, 53, 13), the sensor being configured for capturing said at least one reference signal processing means for extracting information from said at least one captured reference signal and for estimating (63) the position and/or orientation of said at least one sensor processing means for estimating the position and/or orientation of the body of said person processing means for calculating a stability index (67) from said position and/or orientation of the body of said person and from said extracted feet position or center of pressure.
