Walk ratio (step length/cadence) as a summary index of neuromotor control of gait: application to multiple sclerosis

In healthy adults, the step length/cadence ratio [walk ratio (WR) in mm/(steps/min) and normalized for height] is known to be constant around 6.5 mm/(step/min). It is a speed-independent index of the overall neuromotor gait control, in as much as it reflects energy expenditure, balance, between-step variability, and attentional demand. The speed independence of the WR in patients with multiple sclerosis (MS), and its capacity to discriminate (a) across patients with MS and controls and (b) among disability levels in MS were tested. The WR was computed in 30 outpatients with MS [20 women, 10 men; Extended Disability Status Scale (potential range: 0-10, observed median 3.5, range 2.5-5.0)] walking at free speed (range: 0.43-1.67 ms), and in 30 healthy controls (20 women, 10 men) at free and slow speed (range: 0.55-1.67 ms). The WR was 6.38±0.66 in controls versus 5.36±0.86 in patients with MS (P<0.000), independent of age, sex, and walking speed. The WR was 5.95±0.69 and 4.90±0.70 in patients with an Extended Disability Status Scale score (P<0.001) below or above the median, respectively, independent of the disease duration (P<0.000). In patients with MS, the WR is a disability-sensitive index of neuromotor control of gait, and thus a promising outcome measure for treatments aimed at improving motor coordination.