Figure. 1.

Experimental set-up for increasing gait unsteadiness, and definition of step parameters. Subjects walked on an instrumented treadmill while viewing a rear-projected virtual hallway. Visual perturbations to the virtual hallway were applied in the M-L and F-A directions, and their effect on step-by-step foot placement and metabolic rate (measured using indirect calorimetry) were quantified. The length and width of each step was estimated from the instantaneous COP under each foot at corresponding points during the gait cycle. The step distances were used to calculate means and RMS variabilities for each trial. We predicted high sensitivity of step width variability to M-L visual perturbations and a corresponding increase in rate of metabolic energy expenditure.