The functional reach test in people with multiple sclerosis: a reliability and validity study

Limits of stability (LOS) is a major component of balance dysfunction in people with multiple sclerosis (MS). The functional reach test (FRT) is a clinical LOS assessment; however, its psychometric properties have not been investigated in people with MS yet. Objectives: To investigate: (1) the intrarater, interrater, and test-retest reliability of the FRT in people with MS; (2) the minimum detectable change (MDC) in the FRT distances; (3) the concurrent and discriminant validity of the FRT; and (4) the cutoff distance that best discriminates people with MS from healthy people and fallers from non-fallers with MS.

Forty-three people with MS and 36 healthy people participated in this study. The FRT was administered along with the instrumented LOS test, Berg Balance Scale, Four Square Step Test, Timed Up and Go Test, and Expanded Disability Status Scale. The FRT was repeated by the same rater after 2 min from the first test session to determine the intrarater reliability and was simultaneously conducted by two independent raters to determine the interrater reliability. The FRT was also repeated after 7-10 days to determine the test-retest reliability. The reliability was quantified using intraclass correlation coefficients (ICC), Bland-Altman plots, and the MDC. The validity was assessed by correlating the FRT distances with the scores of other measures and by comparing the FRT distances between the MS group and healthy people, and between the fallers and non-fallers in the MS group.

The FRT demonstrated good to excellent intrarater, interrater, and test-retest reliability with an ICC (3,1) of 0.80-0.88 (p < .001), an ICC (3,2) of 0.94-0.97 (p < .001), an ICC (2,3) of 0.84-0.86 (p < .001), respectively. Bland-Altman analyses showed no systematic bias between the assessments. The MDC was 8.28 centimeters. The FRT was correlated with the other outcome measures (correlation coefficients ranged from 0.31 to 0.79, p < .05 for all). Significant differences in the FRT distances were found between people with MS and healthy people; however, no significant difference was found between the fallers and non-fallers with MS (p < .001 and p = .09, respectively). The cutoff distance of 35.5 centimeters best discriminates healthy people from people with MS while of 28.5 centimeters did not discriminate between the fallers and non-fallers with MS.

The FRT is a reliable, valid, and easy-to-administer tool for assessing LOS in people with MS.