Does the six-minute walk test measure walking performance or physical fitness in persons with multiple sclerosis?

There is psychometric evidence that supports the six-minute walk (6MW) as a measure of walking performance, whereas other psychometric data support it as a submaximal measure of physical fitness in persons with MS.

The current cross-sectional study compared measures of walking performance and physical fitness as head-to-head predictors of 6MW distance in a sample of persons with MS across the disability spectrum.

All participants completed the 6MW test, as well as other measures of walking performance (i.e., timed-25 foot walk, gait velocity captured by a GaitRite electronic walkway) and physical fitness (i.e., peak aerobic capacity, lower limb muscular strength).

6MW distance was strongly associated with measures of walking performance and physical fitness, though the correlations were significantly stronger for measures of walking performance than physical fitness (z >  4.04, p <  0.01). Walking performance explained a large portion of variance in 6MW distance (R2 >  0.85), and measures of physical fitness explained minimal variance in 6MW distance over-and-above that of measures of walking performance (ΔR2 <  0.06).

The current results suggest that 6MW distance is primarily a measure of walking performance rather than aerobic and muscular fitness in MS.