Gait Speed in Spinal Muscular Atrophy: A Key Vital Sign Linked to Strength and Fatigability.

INTRODUCTION/AIMS: Gait Speed (GS), a valid and reliable indicator of function and health in multiple populations, has not been explored in spinal muscular atrophy (SMA). The purpose of this study was to characterize GS and gait speed reserves (GSR), and explore associations with strength and fatigability in SMA and healthy controls (HC). METHODS: Data were collected from ambulatory individuals with SMA (n = 14) and controls (HC) (n = 10). Using custom-engineered instrumented insoles, stride velocity (SV) was collected during the Six-Minute Walk Test (6MWT) and 10-m walk/run (10MWR). Three GS variables were identified; SV50th Centile6MWT (SV50C6MWT), 10MWR SV, and SV95th Centile6MWT (SV95C6MWT). Gait speed reserve (GSR) was calculated from 10MWR and SV50C6MWT. Repeated measures analysis of variance assessed differences in GS and GSR across groups. Spearman's Rho was used to assess associations between speed variables and clinical assessments. RESULTS: All speed variables were different within HC (p < 0.001) and SMA (p = 0.002). There was a significant Group × Speed interaction (p < 0.001) with greater differences in HC. GSR was lower in SMA (p < 0.001, d = 2.42). In SMA, thigh strength was associated with all three GS variables and inversely associated with fatigability (p < 0.05). In HC, associations between GS and strength or fatigability were not observed. GSR was not associated with strength, fatigability, or GS in either group. DISCUSSION: GS is diminished in SMA and correlated with strength and fatigability. While reduced in SMA, GSR was not associated with GS, strength, or function. GS is a key vital sign of health and may be a useful biomarker in SMA.