Spectrum analysis in postural strategy on static tests in a healthy population.

INTRODUCTION AND OBJECTIVES The power spectral density can be used to find a hidden behaviour in a physical system. We studied postural behaviour in a healthy population, by means of power spectral density, and compared it with a situation of complete immobility. METHODS A group of healthy volunteers carried out the modified Clinical Test for Sensory Interaction in Balance. A fibre optic gyroscope device was used to record the data. We compared the power spectral density in these tests and with another recording where the device was motionless. We looked for significant differences using the ANOVA test. RESULTS A power peak appeared at 8.4 Hz in all static tests. The static group showed significant differences with all the other tests. We found no statistically significant differences when visual input discriminated between 2 tests. There were statistically significant differences for the proprioceptive input. CONCLUSIONS Brief movements are needed to maintain the quiet stance. The distinctive feature of these movements is a fundamental frequency at 1.4 Hz and a harmonic frequency at 8.4 Hz. Proprioceptive input is essential for balance.