Shorter Distance In 6-minute Walk Test In People With Multiple Sclerosis Demonstrating Leg Strength Asymmetries

Abstract

One of the early signs of Multiple Sclerosis (MS) is weakness on one side of the body, which is experienced by more than 75% of people with MS (PwMS). In addition, up to 92% of PwMS are affected by fatigue. Our previous findings indicate that leg strength asymmetries are associated with imbalanced muscle activity during walking. PURPOSE: To determine the association between leg strength asymmetries and walking characteristics, as indicated by total distance covered and step count, during a 6-minute walk test in PwMS. METHODS: PwMS (aged 46-52 yrs) with self-reported asymmetries (2-5 on a 1-5 scale) and moderate disability (PDDS score 2-6) completed a series of maximal voluntary contractions of the knee extensors on each leg. Subsequently, participants walked as quickly, and safely as possible during a 6-minute walk test in a hallway with 2 cones placed 29 m apart. iPods with built-in accelerometers were strapped on both ankles to detect steps. In addition, ratings of perceived exertion (RPE) and distance covered were recorded every minute. Stride length was then calculated by dividing total distance by step count. RESULTS: The distance covered by the PwMS was 391 ± 110 m with 572 ± 86 steps. The average increase in stride length from minute 1 to minute 6 was 8 ± 4 %. The average difference in leg strength was 27 ± 12 %. The subject with the greatest leg strength asymmetry (37%) demonstrated the shortest distance during the 6-minute walk test (307 m) and the greatest change in stride length (12%). Furthermore, RPE and distance covered each minute remained constant during the 6 minutes. CONCLUSION: These preliminary data indicate that leg strength asymmetries may result in altered walking strategies during a 6-minute walking test in PwMS. While previous studies have used the 6-minute walking test as a measurement of fatigue, in this sample, fatigability, defined as a decline in performance over time, appears to rather manifest itself as changes in walking characteristics.