Coimpairments: Strength and balance as predictors of severe walking disability

Background, Little information is available on the joint effects of multipl e impairments (coimpairments) on the risk of disability. Our aim was to stu dy the joint effects of strength and balance impairments on severe walking disability. Methods. The data are from the baseline of the Women's Health and Aging Stu dy (WHAS), a study of moderately to severely disabled women. A total of 1,0 02 women aged 65 and older participated in the tests, which took place in t heir homes. Severe walking disability was defined as self-reported inabilit y to walk one-quarter mile and customary walling speed in a 4-meter test of less than or equal to 0.4 m/s. Balance was measured as an ability to hold progressively more difficult stands (feet side-by-side, semi-tandem and tan dem stands). Maximal knee extension strength was measured using a hand-held dynamometer. Results. There were 129 women who were severely walking disabled but able t o walk at least minimally. In logistic regression analysis, balance and kne e extension strength were independent predictors of severe walking disabili ty. To study the combined effects, nine groups were formed on the basis of strength tertiles by balance categories in the entire population. In the be st balance category, the crude prevalences of severe walking disability wer e 1.2%, 4.9%, and 14.3% in the highest to lowest strength tertiles. In the middle balance category, the rates were 2.9%, 10.0%, and 45.4.1%, and in th e poorest balance category 4.9%, 22.1%, and 42.6%, correspondingly. The age , body weight, and height-adjusted odds ratios (OR) showed that the risk of severe walking disability in the subgroup with best balance and strength w as less than 5% of the risk in the subgroup with poorest balance and streng th (OR.034, 95% confidence interval [CI].007-. 166). Correspondingly, in th e subgroups with poorest strength and best balance (OR.097, 95% CI.025-.38) or poorest balance and best strength (OR.102, 95% CI.012-.866) the risk wa s about 10%. The age-specific estimates of prevalence of severe walking dis ability in women were: 2.0% for ages 65-74 years, 3.4% for ages 75-84 years , and 9.1% for ages 85 pears and older. Conclusions. The burden of coimpairments seems to be greater than the sum o f single impairments involved. An effective way to reduce severe disabiliti es could be prevention of coimpairments.