Physiologic Responses and Changes in Walking Performance during the Six Minute Walk Test in People with Multiple Sclerosis: A Systematic Review

Background: People with multiple sclerosis (MS) often experience a declination in performance in response to prolonged activities such as the 6MWT. This declination may be associated with MS-related fatigability; however, there is limited evidence exploring the changes that occur during the 6MWT to support this theory. Understanding how walking performance and physiological responses change during the 6MWT in people with MS may help identify the etiology of these changes and guide intervention strategies.

Objectives: The purpose of this systematic review was to examine physiologic responses and changes in walking experienced by people with MS during the 6MWT.

Methods: A search of SCOPUS, CINAHL and Medline databases was conducted in July 2015 using the search terms “six minute walk test AND Multiple Sclerosis”.  Studies that measured walking performance and/or physiologic responses during the 6MWT in a sample of people with MS were included for review.  Two reviewers developed a consensus rating of validity of each study using the Critical Appraisal Skills Programme's (Oxford, UK) Cohort Study Checklist (CSC) which provides as score ranging from 0 (low validity) to 9 (high validity). 

Results: Five studies were included in this systematic review. Each study received a score of 8/9 on the CSC (median 8/9, range 8, interquartile range=0.0). The samples included people with MS with EDSS scores of 0-6.5 or Patient-Determined Disease Steps scores of 0-6.0. Three studies examined differences in walking performance by measuring walking velocity (WV) or distance walked per minute (the factors of WV), two examined rate of oxygen consumption (VO₂), and one examined heart rate (HR).

Conclusions: The samples examined in the reviewed studies demonstrated consistent declines in WV during the 6MWT.  Those studies that examined physiological responses during the 6MWT showed a consistent increase in physiologic activity (i.e. VO₂ and HR) during the first 3 minutes followed by a stabilization for the remainder of the test.  Taken together, these patterns of change suggest that that there is a decline in WV even as the physiologic responses increase during the earlier part of the 6MWT and then remain unchanged once a stable level is reached. One explanation is that fatigue-induced changes in gait may result in inefficient walking patterns that elevate the metabolic cost of walking. This exaggerated demand may play a role in the decline observed in self-selected walking speed during the 6MWT in people with MS. Future research is recommended to examine the interaction between changes in physiologic function and measures of walking efficiency to determine whether the observed declination in performance is a result of diminished fitness, fatigability, or other factors that may be amenable to rehabilitation interventions.