Differences in Functional Performance and Minimal Detectable Change According to Levels of Ankle Plantar Flexor Spasticity in Patients with Chronic Stroke

<b>Background/Objectives</b>: Ankle plantar flexor spasticity after stroke may limit mobility, especially during turning and multi-directional stepping. Evidence on performance differences and measurement properties across spasticity levels is limited. We examined whether performance on the Activities-specific Balance Confidence Scale (ABC Scale), Five Times Sit-to-Stand Test (5xSTS), Figure-of-8 Walk Test (F8WT), and Four-Square Step Test (FSST) differs by spasticity severity, and evaluated test-retest reliability, the intraclass correlation coefficient (ICC), the standard error of measurement (SEM), and the minimal detectable change (MDC). <b>Methods</b>: In an observational cross-sectional comparative study, 54 individuals more than 6 months post-stroke were classified into three groups by the Modified Ashworth Scale (MAS = 0, MAS = 1 - 1+, MAS ≥ 2). Participants completed the ABC Scale, 5xSTS, F8WT, and FSST. One-way analysis of variance with Bonferroni adjustment tested group differences. Reliability was quantified using ICC (2,1); SEM and MDC at the 95% confidence level indexed absolute reliability. <b>Results</b>: No significant differences were found for the ABC Scale or 5xSTS. F8WT and FSST differed by spasticity level (<i>p</i> < 0.05), with poorer performance in the highest-spasticity group versus no spasticity. ICCs were high across assessments. All SEMs were <20% of test-retest means, and all MDCs were <20% of maximum scores. <b>Conclusion</b>: Assessments that require directional change detected differences across spasticity levels, whereas balance confidence and repeated sit-to-stand did not. All measures showed acceptable relative and absolute reliability. Findings support selecting outcomes by spasticity severity and using SEM and MDC as reference values when interpreting change in stroke rehabilitation.