Perception of task duration affects metabolic cost during split-belt adaptation.

Humans continuously adapt locomotor patterns. Whether metabolic cost reduction is the primary objective or a by-product of the observed biomechanical changes during adaptation is not known. The main goal of our study is to determine if perception of task duration affects the adaptation of locomotor patterns to reduce energetic cost during split-belt walking. We tested the hypothesis that individuals who believe they will sustain a locomotor adaptation task for a prolonged time will reduce metabolic cost by adapting toward a walking pattern associated with lower mechanical work. N=14 participants walked on a split-belt treadmill for 10 minutes with knowledge of task duration (group K), while N=15 participants performed the task under the assumption that they would walk for 30 minutes (group U). Both groups walked for 10 minutes with the belts moving at 1.5 and 0.5 m/s, followed by 6 minutes of walking with both belts at 1.0 m/s. We observed a significant main effect of Time (p<0.001, observed power 1.0) and the interaction of Time×Group (p=0.004, observed power 0.84) on metabolic cost. Participants in the U group had a metabolic cost that was 12% lower during adaptation compared to the K group, which did not reduce metabolic cost during adaptation. The metabolic cost reduction observed in group U was not associated with biomechanical changes during adaptation. Our results indicate that metabolic cost reduction has a primary role in tasks that need to be sustained for a prolonged time, and this reduction is not only related to biomechanical factors.