The Energy Cost Of Walking With Increased Step Length Variability

Older adult and neurological populations tend to walk with slower speeds and more gait variability. These gait changes can increase the metabolic cost of walking. Specifically, altering step length and variability away from preferred has been suggested to increase metabolic cost. However, the relationship between the magnitude of step length variability and metabolic cost is still unclear. One way of evaluating variability is through the coefficient of variability (COV). PURPOSE: To determine how increased step length variability impacts the metabolic cost of waking. METHODS: 11 healthy young adults completed 5 minutes of treadmill walking at 1.20 m/s across step length conditions of preferred, 0%, 5% and 10% COV. Rectangles (stepping stones) were projected onto the surface of the treadmill to guide step placements. The COV for these rectangles was manipulated using a MATLAB script that generates perturbations relative to relative to preferred step length. Actual step lengths during the walking tasks were tracked with reflective markers on the feet, while metabolic cost was measured using indirect calorimetry during steady state walking. Changes in metabolic cost across the preferred and three variability conditions was analyzed with a repeated measures ANOVA. RESULTS: Metabolic cost was largest in the 10% condition (4.36 +/- 1.32 W/kg) followed by 5% (4.22 +/- 1.76 W/kg), 0% (4.17 +/- 0.63 W/kg) and preferred (4.04 +/- 0.52 W/kg). However, measured COV did not match projected conditions for 0% (3%), and 10% (7%). For every 1% increase in step length variability, there is an 0.79% increase in metabolic power. CONCLUSIONS: Our results demonstrate that there might be an association between the cost of walking and gait variability. This suggest that the increased cost of walking in older adults and neurological populations is the result of increased gait variability while walking.