Inclusion Criteria:  age 65 or above; score of less than 24/28 in the Tinetti Performance Oriented Mobility Assessment (POMA).  Exclusion Criteria:  total score of less than 24 in the Chinese version of the Mini-Mental State Examination (MMSE-C); presence of any untreated cerebral vascular disease, Parkinson's disease, or any other major neurological deficit; presence of any unstable medical condition that can affect safety during the exercise training; inability to sit and lie down on a Pilates exercise mat on the floor even with assistance.