Objective: To assess the characteristics of the 6-min walk (6MW) in multiple sclerosis (MS) subjects of varied disability, and controls. To assess the correlation of 6MW to subjective measures of fatigue, health status and ambulation using the modified fatigue impact scale (MFIS), short form-36 Health Questionnaire physical component score and MS walking scale (MSWS).
Methods: Forty MS expanded disability status scale [(EDSS) 0-6.5] and 20 control subjects were recruited from a MS outpatient clinic. Subjects completed survey material and three 6MWs with 1-h interval rest in a single study visit.
Results: There was no practice effect or fatigability with repeat 6MW tests with a one-h rest period between test sessions. The 6MW had excellent intra-[intraclass correlation coefficient (ICC) = 0.95] and inter-rater (ICC = 0.91) reliability. MS subjects demonstrated reduced 6MW distance and speed compared with controls (P < 0.0001). Within the MS population 6MW distance was significantly reduced with increasing disability (P = 0.05). Compared with the EDSS, the 6MW had a stronger correlation to subjective measures of ambulation and physical fatigue: MSWS (r = -0.81 versus 0.69) and MFISphy (0.66 versus 0.63).
Conclusions: The 6MW is a feasible, reproducible, and reliable measure in MS. MS subjects demonstrate motor fatigue in both 6MW distance and speed compared with controls. In MS subjects there is an inverse relationship between motor fatigue and disability. 6MW has a strong correlation to subjective measures of ambulation and physical fatigue.