Paper Accepted (May 2022)
The Metabolic Cost of Walking Balance Control and Adaptation in Young Adults.
Shawn Ahuja and Jason R. Franz
Background: Our aim was to quantify the role of metabolic energy cost in governing neuromuscular adaptation to prolonged exposure to optical flow walking balance perturbations in young adults. Research Question: We hypothesized that metabolic cost would increase at the onset of balance perturbations in a manner consistent with wider and shorter steps and increased step-to-step variability. We also hypothesized that metabolic cost would decrease with prolonged exposure in a manner consistent with a return of step width and step length to values seen during normal, unperturbed walking. Methods: Healthy young adults (n=18) walked on a treadmill while viewing a virtual hallway. Optical flow balance perturbations were introduced over a 10-minute interval during a 20-minute walking bout while measuring step kinematics and metabolic energy cost. For all outcome measures, we computed average values during the following four time periods of interest: Pre (minutes 3-5), Early Perturbation (minutes 5-7), Late Perturbation (minutes 13-15), and Post (minutes 18-20). A repeated-measures ANOVA tested for main effects of time, following by post-hoc pairwise comparisons. Results: With the onset of perturbations, participants walked with 3% shorter, 17% wider, and 53-73% more variable steps. These changes were accompanied by a significant 12% increase in net metabolic power compared to walking normally. With prolonged exposure to perturbations, step width and step length tended toward values seen during normal, unperturbed walking – changes accompanied by a 5% reduction in metabolic power (p-values≤0.05). Significance: Our study reveals that the adoption of generalized anticipatory control at the onset of optical flow balance perturbations and the subsequent shift to task-specific reactive control following prolonged exposure have meaningful metabolic consequences. Moreover, our findings suggest that metabolic energy cost may shape the strategies we use to adapt walking balance in response to perturbations.