Abstract
The stability in standing posture was studied in 148 healthy males ranging from 22 to 95 years of age. The subjects stood in the Romberg's posture on a force platform and performed following two tasks: 1) to stand as quietly as possible first with eyes open and then with eyes closed for 20sec, respectively. 2) to shift the center of foot pressure (CFP) voluntarily in the anteroposterior direction without bending the trunk and then maintain several different positions with eyes open for 10sec. The movements of the CFP were displayed on an X-Y recorder and their length (L-value) were calculated with the length analyzer (S-110, Patella). Relative distance from the most hind point of the heel to the center of the CFP traces were calculated using the foot length as 100%. The range between the center of the trace in the maximum anterior position and that in the maximum posterior position was defined as A-P%. In addition, duration of standing on a foot was measured on a floor first with eyes open and then with eyes closed. Mean A-P% markedly reduced while mean L-value during quiet standing slightly increased as a function of age. In approximately a half of the aged subjects who were more than 70 years old, L-value during quiet standing was much the same as younger subjects. Only small number of them had a great range of A-P% like younger subjects. L-value during standing along with shift of the CFP more markedly increased in the aged subjects. Duration of standing on a foot also decreased with an increase in age. There was a tendency for aged subjects who had relatively great A-P% to be capable of standing on a foot for longer duration. The results suggest that the postural adjustments in response to a shift of the CFP appear in the earlier stage of aging rather than the steadiness of the quiet standing. Duration of the subject's ability to stand on a foot appears to be a useful evaluation of the ability to make postural adjustments.
