Background: Postural sway could be separated into several components according to frequencies. Higher frequency sway is indicative of hip strategy but how is it impaired in ataxia patients is still unknown. Methods: Static posturography examination were administered to 37 patients with spinocerebellar ataxia (SCA), 58 patients with the cerebellar type of multiple system atrophy and 53 healthy controls. Energy value trajectory during the four-step sensory organization tests were evaluated by generalized additive mixed model (GAMM). Repeated measures correlation analysis between energy value/proportions and postural performance (total postural sway, fall and tremor occurrence) were also performed. Results: GAMM analysis revealed that the middle frequency band proportion did not increase with test difficulties in MSA and SCA, indicating a failure of frequency shift. Repeated measures correlation analysis revealed that the highest correlation coefficient between energy values were found between MFV and HFV in healthy controls, illustrating components of a complete hip strategy, which was not found in SCA or MSA. In normal adults, there is a significant and positive relationship between MFP and HFP with total energy values, illustrating frequency shifts of normal stance. However, MFP was negatively related with total energy values in SCA (p>0.05) and MSA (pConclusion: Hip strategy was not complete in SCA while it was completely disrupted in MSA, which explains why there were more falls in MSA patients. High frequency band postural sway (>2Hz) is an important component of a complete hip strategy and its origin needs further investigation.
