Eight Functional outcomes, two dimensions: a cross-sectional analysis of scale dependence in spatiotemporal gait determinants after subacute stroke.

BACKGROUND: Spatiotemporal gait parameters have been linked to clinical outcomes after stroke, but whether determinants differ between outcomes is untested in one cohort. OBJECTIVE: To determine how many dimensions eight routinely used outcomes represent, and whether between-outcome differences in determinants reflect construct or scale. METHODS: Cross-sectional study, 244 patients with subacute stroke (Functional Ambulation Category [FAC] ≥2). Fifteen walkway parameters were modeled, with one predictor pool, against Berg Balance Scale (BBS), gait velocity, Timed Up and Go (TUG), 10-meter (10MWT) and 2-minute (2MWT) walk tests, FAC, and Functional Independence Measure (FIM). Principal component analysis assessed dimensionality; partial-F tests and reciprocal transformation tested determinant exchangeability. RESULTS: The outcomes reduced to two components (90.6% of variance): walking capacity (78.0%), loaded by all walking measures and FAC, and one defined by FIM (12.6%); velocity and 10MWT shared 99.4%. Bilateral step length explained BBS, velocity and 2MWT; step-time asymmetry and cadence explained TUG and 10MWT (adjusted R2 0.83-0.92). The temporal block added variance only for time-denominated outcomes (ΔadjR2 = 0.073, 0.077), and reciprocal transformation reversed every profile. Cadence predicted FAC (OR = 1.027, 1.002-1.054, p = 0.037); FIM was unexplained (0.05). CONCLUSION: These outcomes represent two dimensions, and which parameters appear dominant depends on whether an outcome is expressed as a time or a rate, so outcome-specific models are not evidence for outcome-specific training targets. The implication is one of measurement: one primary walking outcome suffices, and independence must be assessed separately.