Posturography is a non-invasive diagnostic method that is used to assess an individual's ability to maintain balance. The main types of posturography are static, dynamic and follow-up posturography. During a follow-up posturography examination, a patient stands on a force platform that is equipped with a monitor. The individual is supposed to balance the body in such a way that the Center of Pressure (CoP) point (presented on a computer screen) coincides with the circle trajectory of a moving visual stimulus. The response to such stimulation provides valuable information about the ability of an individual to maintain their balance. The paper proposes a method, which is based on a Fourier analysis of complex-valued data, that is used to parameterise the posturographic trajectory that is obtained during a follow-up examination. The usefulness of the presented postural stability measures was confirmed by tests that were performed in a group of 30 individuals.