Comparison of power spectrum characteristics of body sway during a static upright standing posture in healthy elderly people and young adults.

This study was designed to compare peak frequency, mean power frequency, and power spectrum of each frequency band of body-sway time series and velocity time series power spectra between 30 healthy elderly people and 30 young adults and to clarify their frequency characteristics. Peak frequency and mean power frequency differed between groups, being higher for elderly persons, and the difference was marked in the front-back direction. When comparing power spectra of three domains (A: 0.02-0.2 Hz, B: 0.2-2.0 Hz, and C: 2.0-10.0 Hz) of an international standard, a significant age-group difference was found only in the front-back direction. Young adults were higher in the low frequency band (A domain) in sway time series, and the elderly group was higher in the high frequency band (C domain) in body-sway velocity time series. However, almost all power spectra of both groups appeared in the low frequency band. The present results suggested frequency characteristics of healthy people occur in the low frequency band, but the elderly group compared with the young adults had more characteristics in the high frequency band. Their frequency characteristics cannot be properly evaluated by the international standard established to screen disorders. It may be necessary for healthy people to have new evaluation frequency sections when considering power spectrum characteristics of sway time series and sway-velocity time series.