Power spectral density analysis of the standing sway of males

Application of power spectral density analysis to normal human standing sway showed that the power in sway was unevenly distributed among various frequencies below 1.0 Hz. Ss were divided, with regard to antero-posterior sway, into two types on the basis of the frequencies at which peaks of power occurred. The same Ss were divided into four types, with regard to lateral sway, using similar criteria. The different types appear to represent normal variations in the basic mechanism for standing upright.