Body-sway characteristics during a static upright posture in the elderly

Aim: This study aimed to determine the reliability and sex and age-level differences of body-sway parameters, based on center of pressure (COP) measurements, during a static upright posture in the elderly and to clarify their body-sway characteristics in comparison with those of young adults. Methods: The subjects were 50 healthy elderly and 50 healthy young adults. They had no evidence or known history of disorder. The data sampling frequency was 20 Hz. Thirty-six highly reliable parameters were selected from the following seven domains: distance; position; distribution of amplitude; area; velocity; power spectrum; and vector. In addition, four body-sway factors (unit time sway, front-back sway and a left-right sway and the high-frequency band power) were also measured. Results: In the elderly, most body-sway parameters had very high reliability and did not show significant sex or age-level differences. The degree of body sway was greater in the elderly than in young adults, and marked differences were found, especially in sway velocity and periodicity. The four body-sway factors showed almost the same tendency as the 32 sway parameters. Conclusion: We judged that the body sway in the elderly showed large individual differences. Approximately 10% of the elderly subjects may be outside the standard range as compared to young adults, mainly in parameters relating to velocity and spectrum. Because the body-sway characteristics of the elderly are considerably different from those of young adults, we may need unique criteria to evaluate their body sway.