Postural Sway of the Elderly Males and Females during Quiet Standing and Squat-and-Stand Movement

In this paper, COP (center of pressure) during quiet standing and squat-and-stand movement was analyzed to compare the postural control of young and elderly subjects with special interest in the elderly females who were reported to have higher fall rate than the elderly males. Subjects include the young subjects (10 males: 21.8 +/- 2.6yrs, 10 females: 20.4 +/- 0.3yrs) and the elderly subjects (8 males: 75.5 +/- 4yrs, 8 females: 72.3 +/- 3.5yrs). Analysis parameters were the mean of the distance between the instantaneous COP and the average COP (COP distance) and the mean of the COP movement velocity (COP velocity) in both AP (anterio-posterior) and NIL (medio-lateral) directions. During quiet standing, the COP distance in NIL direction of elderly females was significantly greater than that of elderly males and the COP velocity of elderly females in both NIL and AP direction were significantly greater than those of all the other groups. During squat-and-stand movement, the COP distance of elderly females was not significantly different with that of the elderly males. However, the COP velocity of elderly females was significantly greater than that of all the other groups. The large lateral weight shift (COP distance) of elderly females during quiet standing may explain their greater fall rate. However, this does not apply to squat-and-stand movement. In contrast, COP velocity results show that the elderly females' COP is rapidly trembling compared to that of elderly males during both quiet standing and squat-and-stand movement. This result suggests that rapid trembling or postural sway may reflect the reduced postural control ability and higher risk of fall in elderly females.