Frequency spectral characteristics of standing balance with partial foot support

The purpose of the study was to investigate the changes of spectral frequency characteristics of standing balance control under the conditions of reducing foot support base. Eight female and eight male young adults (mean age 21.2±1.4 years) were tested for standing balance under ten test conditions. Ground reaction forces measured with a force platform during repeated trials of standing were analyzed using spectral analysis. The median spectral frequencies and the absolute slopes in the anterior-posterior and the medial-lateral directions were taken as variables. Results showed that the spectral characteristics of postural forces were significantly affected by reducing foot support base in the anterior-posterior direction. The median frequency in the A/P direction was higher when reducing both sides of foot support. It implied that subjects suffered more from an imperfect ankle control with reducing the base of support, and more emphasis needed to be placed on the perturbations that disrupted the A/P stability.