The Influence of Initial Bipedal Stance Width on the Clinical Measurement of Unipedal Balance Time

ObjectiveTo determine the effect of varying initial bipedal stance width (ISW) on the clinical measurement of unipedal balance time (UBT).DesignObservational, cross-sectional study.SettingAcademic physiatric outpatient facility.SubjectsThirty-one clinic subjects with neuromuscular and/or musculoskeletal conditions known to influence mobility and 30 similarly-aged healthy subjects.MethodsDemographic and clinical information were recorded. UBT was determined under 3 distinct conditions by varying bipedal intermalleolar distance: (1) ISW of 0.3 body height; (2) ISW of 0.05 body height; and (3) ISW of 0 body height. The last was accomplished by subjects assuming unipedal balance while using the hands on a horizontal surface for stabilization. Subjects lifted the contralateral foot (or hands in the case of 0 body height condition) in response to a cadenced command to minimize variation in rate of weight transfer.Main Outcome MeasureUBT under each of the 3 ISW conditions.ResultsMean UBT increased with decreasing ISW, and the differences were significant when comparing each ISW with the next smaller. Healthy subjects demonstrated greater UBT than clinic subjects at each ISW, but the magnitude of these group differences were similar across ISW condition. A UBT >10 seconds in the 0.3 body height ISW was the best discriminator between clinic and healthy subjects.ConclusionBecause UBT varies with ISW, standardization of ISW is necessary for accurate within-subject, and between-subject, comparisons in UBT. Healthy subjects were best differentiated from clinic subjects by UBT >10 seconds in the 0.3 body height ISW condition.