@article {847, title = {Too much or too little step width variability is associated with a fall history in older persons who walk at or near normal gait speed.}, journal = {J Neuroeng Rehabil}, volume = {2}, year = {2005}, month = {2005 Jul 26}, pages = {21}, abstract = {

BACKGROUND: Decreased gait speed and increased stride time, stride length, double support time, and stance time variability have consistently been associated with falling whereas step width variability has not been strongly related to falls. The purpose was to examine the linear and nonlinear associations between gait variability and fall history in older persons and to examine the influence of gait speed.

METHODS: Gait characteristics and fall history were obtained in 503 older adults (mean age = 79; 61\% female) participating in the Cardiovascular Health Study who could ambulate independently. Gait characteristics were recorded from two trials on a 4 meter computerized walkway at the subject{\textquoteright}s self-selected walking speed. Gait variability was calculated as the coefficient of variation. The presence of a fall in the past 12 months was determined by interview. The nonlinear association between gait variability and fall history was examined using a simple three level classification derived from the distribution of the data and from literature based cut-points. Multivariate logistic regression was used to examine the association between step width variability (extreme or moderate) and fall history stratifying by gait speed (1.0 m/s) and controlling for age and gender.

RESULTS: Step length, stance time, and step time variability did not differ with respect to fall history (p > .33). Individuals with extreme step width variability (either low or high step width variability) were more likely to report a fall in the past year than individuals with moderate step width variability. In individuals who walked > or = 1.0 m/s (n = 281), after controlling for age, gender, and gait speed, compared to individuals with moderate step width variability individuals with either low or high step width variability were more likely to have fallen in the past year (OR and 95\% CI 4.38 [1.79-10.72]). The association between step width variability and fall history was not significant in individuals who walked < 1.0 m/s (n = 224).

CONCLUSION: Extreme (either too little or too much) step width variability is associated with falls in the past year in older persons who walk at or near normal gait speed and not in older persons who walk slowly (< 1.0 m/s).

}, issn = {1743-0003}, doi = {10.1186/1743-0003-2-21}, author = {Brach, Jennifer S and Berlin, Jaime E and VanSwearingen, Jessie M and Newman, Anne B and Studenski, Stephanie A} } @article {987, title = {Gait variability and the risk of incident mobility disability in community-dwelling older adults.}, journal = {J Gerontol A Biol Sci Med Sci}, volume = {62}, year = {2007}, month = {2007 Sep}, pages = {983-8}, abstract = {

BACKGROUND: Gait speed is a strong predictor of incident walking disability. The objective was to determine if gait variability adds to the prediction of incident mobility disability independent of gait speed.

METHODS: Participants included 379 older adults (mean age = 79 years; 78\% Caucasian, and 40\% men) in the Cardiovascular Health Study at the Pittsburgh site. All could ambulate independently and reported no difficulty walking a half mile. Gait characteristics were determined from a 4-meter computerized walkway. For each gait parameter, variability was defined as the standard deviation from the individual steps from two passes. Incident walking disability was obtained by phone interview every 6 months for 54 months and was defined as new difficulty walking a half mile or inability to walk a half mile.

RESULTS: Of the 379 participants, 222 (58.6\%) developed incident mobility disability. In unadjusted Cox proportional hazards models gait speed, mean step length, mean stance time, and stance time variability were associated with incident mobility disability. After adjusting for gait speed, demographics, chronic conditions, prescription medications, health status, and physical activity level, only stance time variability remained an important indicator of disability. In the adjusted model, an increase in stance time variability of 0.01 seconds was associated with a 13\% higher incidence of mobility disability (hazard ratio 1.13, 95\% confidence interval, 1.01-1.27).

CONCLUSIONS: Stance time variability is an independent predictor of future mobility disability. Future efforts are needed to determine whether interventions that decrease stance time variability will also delay mobility disability.

}, keywords = {Aged, Aged, 80 and over, Aging, Cohort Studies, Female, Gait, Gait Disorders, Neurologic, Humans, Male, Mobility Limitation, Prospective Studies, Risk Factors, Walking}, issn = {1079-5006}, doi = {10.1093/gerona/62.9.983}, author = {Brach, Jennifer S and Studenski, Stephanie A and Perera, Subashan and VanSwearingen, Jessie M and Newman, Anne B} } @article {970, title = {Stance time and step width variability have unique contributing impairments in older persons.}, journal = {Gait Posture}, volume = {27}, year = {2008}, month = {2008 Apr}, pages = {431-9}, abstract = {

Gait variability may have multiple causes. We hypothesized that central nervous system (CNS) impairments would affect motor control and be manifested as increased stance time and step length variability, while sensory impairments would affect balance and be manifested as increased step width variability. Older adults (mean+/-standard deviation (S.D.) age=79.4+/-4.1, n=558) from the Pittsburgh site of the Cardiovascular Health Study participated. The S.D. across steps was the indicator of gait variability, determined for three gait measures, step length, stance time and step width, using a computerized walkway. Impairment measures included CNS function (modified mini-mental state examination, Trails A and B, Digit Symbol Substitution, finger tapping), sensory function (lower extremity (LE) vibration, vision), strength (grip strength, repeated chair stands), mood, and LE pain. Linear regression models were fit for the three gait variability characteristics using impairment measures as independent variables, adjusted for age, race, gender, and height. Analyses were repeated stratified by gait speed. All measures of CNS impairment were directly related to stance time variability (p<0.01), with increased CNS impairment associated with increased stance time variability. CNS impairments were not related to step length or width variability. Both sensory impairments were inversely related to step width (p<0.01) but not step length or stance time variability. CNS impairments affected stance time variability especially in slow walkers while sensory impairments affected step width variability in fast walkers. Specific patterns of gait variability may imply different underlying causes. Types of gait variability should be specified. Interventions may be targeted at specific types of gait variability.

}, keywords = {Aged, Aged, 80 and over, Biomechanical Phenomena, Female, Gait Disorders, Neurologic, Humans, Linear Models, Longitudinal Studies, Male, Neuropsychological Tests, Postural Balance, Range of Motion, Articular, Risk Factors, Signal Processing, Computer-Assisted}, issn = {0966-6362}, doi = {10.1016/j.gaitpost.2007.05.016}, author = {Brach, Jennifer S and Studenski, Stephanie and Perera, Subashan and VanSwearingen, Jessie M and Newman, Anne B} } @article {1363, title = {Use of stance time variability for predicting mobility disability in community-dwelling older persons: a prospective study.}, journal = {J Geriatr Phys Ther}, volume = {35}, year = {2012}, month = {2012 Jul-Sep}, pages = {112-7}, abstract = {

BACKGROUND AND PURPOSE: Mobility disability is a serious and frequent adverse health outcome associated with aging. Early identification of individuals at risk for mobility disability is important if interventions to prevent disability are to be instituted. The objectives of this prospective study were to (1) determine the magnitude of stance time variability (STV) that discriminates individuals who currently have mobility disability (prevalent mobility disability) and (2) determine the magnitude of STV that predicts a new onset of mobility disability at 1 year (incident mobility disability).

METHODS: A total of 552 community-dwelling older adults were evaluated as part of the Cardiovascular Health Study, a longitudinal cohort study. Stance time, in milliseconds, was determined from 2 passes on a 4-m computerized walkway at self-selected walking speed, and STV was defined as the standard deviation from approximately 12 individual steps. Mobility disability was defined as self-reported difficulty walking a one-half mile. Receiver operating characteristic (ROC) curves were plotted to determine an optimal cutoff value for STV for prevalent and incident mobility disability, and the area under the receiver operating characteristic curve (AUC) was computed.

RESULTS: The optimal cutoff score for STV (maximizing sensitivity and specificity) for prevalent mobility disability was 0.037 seconds (sensitivity = 65\%, specificity = 65\%, AUC = 0.70) and for incident 1-year mobility disability was 0.034 seconds (sensitivity = 61\%, specificity = 60\%, AUC = 0.65). The use of likelihood ratios demonstrated a gradient of risk across values of STV, with mobility risk increasing as values of STV increased.

DISCUSSION AND CONCLUSION: Values of STV may be useful in identifying older adults with mobility disability and at risk for future disability. We recommend the more conservative estimate for identifying risk, STV = 0.034 seconds, which maximizes the sensitivity and minimizes false negatives. The relatively modest values on the validity indices could possibly be improved by increasing the reliability of the measurement of STV. Clinicians should interpret the cutoff values liberally and use STV in conjunction with other measures until further work is completed to validate STV as an indicator of mobility disability.

}, keywords = {Aged, Aged, 80 and over, Disability Evaluation, Female, Gait, Geriatric Assessment, Humans, Independent Living, Male, Mobility Limitation, Physical Therapy Modalities, Postural Balance, Prospective Studies, Reproducibility of Results}, issn = {2152-0895}, doi = {10.1519/JPT.0b013e318243e5f9}, author = {Brach, Jennifer S and Wert, David and VanSwearingen, Jessie M and Newman, Anne B and Studenski, Stephanie A} }