Power spectrum of the fast Fourier transform for measurement of standing balance.

Power spectrum of the force moment generated from the fast Fourier transform (FFT) was utilised to evaluate standing balance on a force platform. The principles on generating and analysing an FFT spectrum from the output of the force platform are illustrated. Test-retest reliability of twelve healthy young people (age = 26 +/- 4 years) was performed with the preferred leg stance. The intraclass correlation coefficient (ICC), R, of mean power (P), spectral area (Sx) and maximum power (Px) were 0.89, 0.85 and 0.89 respectively, indicating that the spectral parameters are reliable quantitative measures of balance. Pearson product moment (PPM), r, of these spectral parameters were 0.95, 0.85 and 0.95 respectively showing that these spectral parameters are significantly correlated (p < 0.01). A comparison was made with respect to the one legged stance and two legged stance steadiness. The one legged stance (Sx = 95.75 cm.Hz) was significantly less stable than the two legged stance (Sx = 41.58 cm.Hz) with a value of 9.37. Moreover, the one legged stance was highly correlated to the two legged stance (r = 0.84), indicating that, in general, a subject who has a stable one legged stance should have a stable two legged stance.