ABSTRACT
According to cross-sectional studies, decreased postural stability, assessed by center of pressure (COP) sway, has been remarkable over the past 60 years, and has become one of the impairment factors for quality of life in the elderly. In the present study, in order to determine whether exercise training, consisting of bicycle ergometer and strength training inhibits decreased postural stability for elderly individuals (60 years of age or more), we investigated changes in COP sway and plantar flexors muscle volume. Healthy male (n=9) and female (n=8) subjects aged 62 to 76 yrs participated in the present study. Subjects were requested to maintain a quiet standing barefoot position on a force platform (type 9281B, Kistler) with their eyes opened or closed. Mean velocity of COP (COP sway length/time) was calculated from anterior-posterior COP sway from force platform data. From the spectral analysis of COP sway, low (0-1 Hz) and high (1 -10 Hz) frequency components of COP series were extracted. The muscle volume of the plantar flexors muscle group was estimated from multi-regression analysis based on measured muscle thickness at the lower leg posterior site using an ultrasonographic apparatus (SSD-500, Aloka) . Mean velocity of COP significantly (P< 0.05) decreased due to training, and this was accompanied by a decrease in COP sway high frequency components. On the other hand, COP sway low frequency components and muscle volume did not change. These findings suggest that an inhibition of decreased postural stability in the elderly is not mainly related to muscle volume, but to improvement of a feedback system from somatosensory function. With respect to the elderly, who have a larger mean velocity of COP, however, postural stability could be related to muscle volume.