Difference in static and dynamic stability between flexible flatfeet and neutral feet.

Different postural stability may be a contributor to secondary injuries in individuals with flexible flatfeet (FF) compared to those with neutral feet (NF). However, the differences between static and dynamic stability of FF and NF have not been examined. This study compared the static and dynamic stability of subjects with FF and NF and investigated the relationship between static and dynamic stability. Twenty-eight subjects (14 each in the FF and NF groups) performed three tasks (single leg standing with eyes open, with eyes closed, and the Y balance test). We quantified the center of pressure (COP) speed and Y balance test score (Y score) within the tasks. COP speed was significantly greater in the FF group than in the NF group under both conditions (eyes open and closed) and directions (anteroposterior and mediolateral). Y scores did not differ significantly between the two groups. No significant relationship was observed between the COP speed and Y score in either group. These results show that individuals with FF have different static stabilities, but not dynamic stabilities, compared with those with NF. This might indicate the absence of a relationship between static and dynamic stabilities.