Sampling duration effects on centre of pressure summary measures.

The purpose of the present study was to examine the effect of sample duration on the magnitude and reliability of centre of pressure (COP) summary measures commonly used to characterize the control of upright stance. COP was recorded from 49 participants who stood quietly during three consecutive 120 s trials. Each record was subdivided into 15, 30, 60 and 120 s samples and root mean square (RMS), mean power frequency (MPF) and mean position of COP were calculated for each sample. RMS significantly increased and MPF values significantly decreased as sample duration increased. Substantial increases in the reliability of both RMS and MPF were observed with increased sample duration.