Perception of unilateral weightbearing during unilateral and bilateral upright stance

To compare the effect of stance (unilateral vs bilateral) and of weightbearing target (25%, 50%, 75%) on error in weightbearing perception, two groups, unilateral and bilateral, of 30 comparable subjects were tested. Weightbearing was measured while subjects stood on digital scales; bilateral stance was accomplished using two scales, and unilateral stance was accomplished using a walker and a single scale. The subject's error in perceiving weightbearing at each target level was assessed by taking the absolute value of the target percent weightbearing minus the mean actual percent weightbearing. The mean errors at the 25, 50 and 75% targets were 6.5, 3.2, 17.6% for the unilateral group and 3.1, 1.4, 3.8% for the bilateral group. A two-way analysis of variance indicated the magnitude of error differed between groups and target levels, with a greater over-all error displayed by the unilateral weightbearing group. Our results suggest that adults are less accurate in judging weightbearing while standing on one, rather than on two, lower extremities. Clinicians should not expect patients to follow accurately instructions to weightbear at a specific percentage of full weight, particularly when using an assistive device to adjust weightbearing.