The Effect of Walking-Related Motor Fatigability during the 6-Minute Walk Test on Temporal-Spatial Parameters of Gait in People with Multiple Sclerosis

Background: Motor fatigability, a measurable change in performance with sustained use, affects many people with MS, and may result in changes in walking and gait. A recent study described the Distance Walked Index (DWI): the percentage change in distance walked between the 1st and 6th minutes of a 6-Minute Walk Test (6MWT). The changes that occur in other temporal-spatial parameters of gait due to fatigability during the 6MWT have not been described.

Objectives: To describe changes in temporal-spatial parameters of gait between the 1st and 6^thminutes of a 6MWT in people with moderate MS-related disability.

Methods: 26 people with a confirmed MS diagnosis (20 women, median EDSS 4.0 (IQR 2.0, range 2.5-6.0)) participated in the study. Participants performed a modified 6MWT without walking assistive devices. An instrumented walkway (GAITRite, CIR Systems, Sparta, NJ) was laid in the pathway. Data was collected during each pass over the walkway, then parsed into mean values for the 1^st and 6^th minutes of the 6MWT using PKMAS Gait Analysis Software (Protokinetics, Havertown, PA). Outcomes included mean walking velocity (WV) and cadence (CAD), and means and coefficients of variation (CV, i.e. step-to-step variability) of step length (SL), step time (ST) stride velocity (SV), stance time (StaT), swing time (SwiT), single limb support time (SLS), and double limb support time (DLS). Differences between 1^st and 6^thminutes were analyzed with parametric or non-parametric tests with an a priori alpha of .05.

Results: Significant decreases between 1^st to 6^thminutes were found in mean WV, CAD, SL, SV, and in CVs of SV, StaT and DLS. Significant increases were found in mean values of StaT and DLS. No change was found in mean ST, SwiT or SLS, or in variability of SL, ST, SwiT, or SLS.

Conclusions: Participants took slower, fewer and shorter steps, and spent more time in stance and double-limb support during the 6th minute of the 6MWT compared to the 1^st.  This indicates that both temporal and spatial factors contributed to the decline in WV (DWI) seen in this and other studies. The decrease in CV of SV, StaT and DLS must be interpreted with caution as the effect of variability on gait is equivocal: some interpret reduced variability as an improvement and others as a worsening. Collectively, the changes found here are thought to increase walking stability. Our interpretation is that fatigability induced by the repeated use of muscles of locomotion contributed to the worsening in mean values and decreases in movement variability from 1^st to the 6^th minutes of the 6MWT. Further research is needed to develop models that identify which factors are the most robust contributors to the deterioration in walking function seen during the 6MWT. Whether these changes are a direct result of muscle fatigability or a response to changes in other systems (e.g. sensation) should also be explored. Once clearly identified, rehabilitation programs can be designed to address the most critical factors.