The Spring Scale Test: a reliable and valid tool for explaining fall history.

BACKGROUND & PURPOSE Although perturbations can result in falls, objective practical tests of balance that incorporate perturbations have not received as much attention as other balance measures. The purposes of this study were to: (1) describe a new clinical waist pull perturbation balance test protocol, the Spring Scale Test (SST), (2) determine the test-retest reliability of the SST, and (3) examine the convergent and known groups validity of the SST relative to 4 other balance related measures. METHODS Fifty-eight community-dwelling older adults underwent same-day test-retest of the SST, with predictable, one-pound incremental, horizontal sagittal plane manual waist pulls. Twenty-nine subjects (mean age 83.5) had at least one fall in the prior 2 years. Twenty-nine subjects (mean age 78.0) were nonfallers. RESULTS The mean (SD) SST performance of 7.5% (1.4) of Total Body Weight (TBW) for fallers and 12.3% (1.7) TBW for nonfallers differed significantly (p < .001). High test-retest reliability was supported by ICC of 0.94 [95% CI = 0.89 - 0.96], a method error (ME) of 0.74 and coefficient of variation of the ME of 7.25%. There was moderate to good convergent validity of the SST with all 4 relevant measures of gait and balance: gait speed (r = 0.53, p = .001), single limb stance (r = - 0.54, p = .001), tandem stance (r = 0.55, p = .001), Timed Up and Go (r = - 0.67, p=.001). The SST score at 10% TBW had high known groups validity with the area under the receiver operating characteristic curve of 0.99, sensitivity of.93 and specificity of.97. Logistic regression revealed that no other variable added to the explanation of fall status once the variance attributable to the SST 10% TBW (91.1%) was included in the predictive equation. CONCLUSIONS The SST is a quantitative, reliable, and valid clinical measure of standing balance. The SST 10% TBW cutoff score was the most discriminating indicator of fall history.