VALUES OF STANCE TIME VARIABILITY RELATED TO MOBILITY DISABILITY.

Abstract

Purpose/Hypothesis: Greater stance time variability (STV) is related to incident mobility disability independent of gait speed. We wished to confirm this association and determine the magnitude of STV that potentially discriminates mobility disability in a sample of older adults diverse in gait speed and in a sub-sample with normal gait speed. Subjects: This crosssectional study included 544 older adults (mean age=79.4; 39% men; 23% black) of the Cardiovascular Health Study from the Pittsburgh site. Materials/Methods: Stance time, in milliseconds (ms), was determined from 2 passes on a 4-meter computerized walkway at self-selected walking speed, and STV was defined as the standard deviation (SD) from approximately 12 individual steps. Mobility disability was defined as self-reported difficulty walking a half mile. A t-test was used to compare STV between individuals with and without mobility disability. Receiver operating characteristic (ROC) curves were plotted to determine an optimal cutoff value for stance time variability, and the area under the ROC curve was computed. Analyses were repeated in a subset with gait speed ≥ 1.0 meters/second. Results: Individuals without mobility disability (n= 419; mean STV=35.5 ms; SD=17.6 ms) were less variable in stance time than individuals with mobility disability (n=125; mean STV=51.2 ms; SD=31.1; p< 0.001). A STV≥36.5 ms has 66% sensitivity and 63% specificity for identifying mobility disability. Area under the ROC curve was 0.696. In those who walk faster than 1.0 meters/second, STV≥30.5 ms has 60% sensitivity and 62% specificity for identifying mobility disability. Area under the ROC curve was 0.618. Conclusions: Greater STV is associated with mobility disability in community-dwelling older adults. Clinical Relevance: A value of STV≥36.5 ms, is a potentially useful clinical indicator of mobility disability in older adults. In those with near normal walking speed (gait speed ≥ 1.0 meters/second) a lower threshold value of STV (≥30.5 ms) may be more appropriate for identifying disability.