Abstract: BACKGROUND: Stability of the support surface and visual input are important factors affecting static balance, but most of the studies on the balance ability of elderly with mild cognitive impairment have focused on the stable hard support surface, and the control of static balance on the unstable support surface under different visual input conditions is not known.
OBJECTIVE: To investigate the static balance ability of the elderly with mild cognitive impairment on soft and hard support surfaces under different visual input conditions.
METHODS: Twenty-one elderly people with mild cognitive impairment and nineteen elderly people with normal cognition were selected for the study, and the Kistler three-dimensional dynamometer was used to conduct four tests: standing with two feet on hard support surface with eyes open, standing with two feet on soft support surface with eyes open, standing with two feet on hard support surface with eyes closed, standing with two feet on soft support surface with eyes closed, and standing with two feet on soft support surface with eyes closed, and the duration of each test was 30 seconds. The plantar center of pressure data were collected and compared between the two groups under different visual conditions on the soft and hard support surfaces.
RESULTS AND CONCLUSION: (1) Under the condition of visual input, the total excursions (soft support surface: P=0.003), the total excursions-medial-lateral sides (soft support surface: P=0.001, hard support surface: P < 0.001) and the 95% confidence ellipse area (soft support surface: P=0.001, hard support surface: P < 0.001) of the center of pressure in the elderly with mild cognitive impairment on the soft and hard support surfaces were significantly higher than those of the elderly with normal cognition. (2) In the absence of visual input, the root mean square distance (P=0.014), the root mean square distance-medial-lateral sides (P=0.014), and the 95% confidence ellipse area (P=0.001) of center of pressure in the elderly with mild cognitive impairment on the soft support surfaces were significantly higher than those of the elderly with normal cognition, but there were no significant differences between the groups on the hard support surface (P > 0.05). (3) These findings confirm that compared with the elderly with normal cognition who could make full use of visual sensory input to maintain body balance on the soft and hard support surfaces, mild cognitive impairment elderly presented a deficit in balance function. In particular, mild cognitive impairment elderly relied more on ankle proprioception to maintain balance when visual interference was present, suggesting that mild cognitive impairment elderly should focus on strengthening ankle proprioceptive training. 

Key words: mild cognitive impairment, elderly, static balance, support surface, center of pressure