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Objectives: Difficulty with sit-to-stand (STS) is a neuromuscular performance risk factor associated with falls. The ability to identify impaired motor patterns in complex activities of daily living is the first step in designing assistive devices to evaluate balance and decrease falling in balance-impaired populations. The objective of this study was to determine whether quantitative measures of STS can easily be identified and whether they correlate with increased fall risk in persons with Parkinson's Disease (PD).
Clinical Relevance: With the rapidly increasing population of fall-prone elderly veterans, methods for fall prevention are urgently needed. Our collaborators have hypothesized that some motor symptoms of Parkinsonism may be alleviated by visual, auditory and/or tactile feedback provided upon real-time recognition of impaired motor patterns (e.g. initiation of gait after STS). A next-generation WAMAS is being designed with these capabilities in mind, for trial in a randomly selected Parkinson's population.
Methods: Seventeen ambulatory PD subjects were asked to perform 14 static balance tasks varying in difficulty from sitting balance to one-legged stance. Tasks were scored on a Qualitative Balance Scale (QBS) by a clinician. Subjects also completed a self-report mobility history from which a fall injury index (FI) was derived. STS was performed at normal speed, arms crossed (unless unable), and recorded using a wearable accelerometric motion analysis system (WAMAS). Video of STS was synchronized to start and stop of data acquisition. The WAMAS unit consists of two 3- axis sensors on eyeglass frames to measure head motion, and two sensors above each hip on a belt at the waist, along with a self-contained data acquisition package. Time between maximum and minimum values (TMM) of averaged right and left waist vector magnitudes and values of maximum (tmax) and minimum (tmin) acceleration vector magnitudes were evaluated. Data were compared by Pearson's Product Moment Correlation.
Results: While subjects used a variety of methods (i.e.. using hands vs not using hands) to perform STS, maximum and minimum vector magnitude peaks were consistent with specific kinematic events. The maximum peak (preceding the minimum) corresponds to end of momentum transfer and the minimum is the end of the accelerative phase of extension during STS. The time between the maximum and minimum corresponds to the period of greatest instability during the task. There was high correlation (p<.005) between QBS scores and FI and a low to moderate correlation (p<.005) between TMM and FI. No correlation existed between FI and tmin or tmax. Subjects who fell more than 6 times in the last year were more likely to have sit-back failures, increasing TMM substantially.
Conclusions: STS is a complex task to analyze. The ability to easily recognize key kinematic events and the moderate correlation to the Fl shows the potential of using accelerometry in assessing complex motor tasks to be used in fall prevention.
Acknowledgments: VA Rehabilitation R&D Merit Review projects E601-2RA, -3RA. We thank Dr. James Tetrud of the Parkinsons Institute for referral of subjects and his continued interest.