Simultaneous measurement of body center of pressure and center of gravity during upright stance. Part II: Amplitude and frequency data

In this paper (Part II) we present amplitude and frequency data on simultaneously measured excursions of the body center of gravity (COG) and center of pressure (COP). The excursions were measured from six subjects during 10-s trials of three upright postural stances: standing on both legs or double stance with eyes open (DSEO), double stance with eyes closed (DSEC), and standing on one leg or single stance with eyes open (SSEO). This study represents the first attempt to describe the normative characteristics and stance-dependent differences between the anteroposterior and mediolateral components of both the COP and COG signals, measured from multiple individuals by the technique described in Part 1. We quantified the anteroposterior and mediolateral excursions of the COP and COG using amplitude and frequency measures, and their planar excursions using 95% confidence ellipses. Although the COP-based amplitude measures were significantly greater than their COG-based counterparts, the amplitude and frequency measures of both were highly correlated in all stances. The results support the continued use of COP-based measures to quantify impaired balance during upright stance.