Sensitivity of Local Dynamic Stability of Over-Ground Walking to Balance Impairment Due to Galvanic Vestibular Stimulation

Impaired balance control during gait can be detected by local dynamic stability measures. For clinical applications, the use of a treadmill may be limiting. Therefore, the aim of this study was to test sensitivity of these stability measures collected during short episodes of over-ground walking by comparing normal to impaired balance control. Galvanic vestibular stimulation (GVS) was used to impair balance control in 12 healthy adults, while walking up and down a 10 m hallway. Trunk kinematics, collected by an inertial sensor, were divided into episodes of one stroll along the hallway. Local dynamic stability was quantified using short-term Lyapunov exponents (lambda(s)), and subjected to a bootstrap analysis to determine the effects of number of episodes analysed on precision and sensitivity of the measure. lambda(s) increased from 0.50 +/- A 0.06 to 0.56 +/- A 0.08 (p = 0.0045) when walking with GVS. With increasing number of episodes, coefficients of variation decreased from 10 +/- A 1.3% to 5 +/- A 0.7% and the number of p values > 0.05 from 42 to 3.5%, indicating that both precision of estimates of lambda(s) and sensitivity to the effect of GVS increased. lambda(s) calculated over multiple episodes of over-ground walking appears to be a suitable measure to calculate local dynamic stability on group level.