Motor fatigue measurement by distance-induced slow down of walking speed in multiple sclerosis

Background: Motor fatigue and ambulation impairment are prominent clinical features of
people with multiple sclerosis (pMS). We hypothesized that a multimodal and comparative
assessment of walking speed on short and long distance would allow a better delineation and
quantification of gait fatigability in pMS.
Objectives: To compare 4 walking paradigms: the timed 25-foot walk (T25FW), a corrected
version of the T25FW with dynamic start (T25FW+), the timed 100-meter walk (T100MW)
and the timed 500-meter walk (T500MW).
Methods: Thirty controls and 81 pMS performed the 4 walking tests in a single study visit.
Results: The 4 walking tests were performed with a slower WS in pMS compared to controls
even in subgroups with minimal disability. The finishing speed of the last 100-meter of the
T500MW was the slowest measurable WS whereas the T25FW+ provided the fastest
measurable WS. The ratio between such slowest and fastest WS (Deceleration Index, DI) was
significantly lower only in pMS with EDSS 4.0-6.0, a pyramidal or cerebellar functional
system score reaching 3 or a maximum reported walking distance !4000m.
Conclusion: The motor fatigue which triggers gait deceleration over a sustained effort in pMS
can be measured by the WS ratio between performances on a very short distance and the
finishing pace on a longer more demanding task. The absolute walking speed is abnormal
early in MS whatever the distance of effort when patients are unaware of ambulation
impairment. In contrast, the DI-measured ambulation fatigability appears to take place later in the disease course.