Perception of task duration influences metabolic cost during split-belt adaptation and biomechanics during both adaptation and post-adaptation.

Humans continuously adapt locomotor patterns. In laboratory settings, split-belt treadmills have been used to study locomotor adaptation. 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. We tested the hypothesis that individuals who believe they will sustain a split-belt adaptation task for a prolonged time will adapt toward a walking pattern associated with lower cost. N=14 participants adapted for 10 minutes with knowledge of time remaining (group K), while N=15 participants adapted under the assumption that they would walk for 30 minutes with no knowledge of time elapsed or time remaining (group U). Both groups adapted for 10 minutes. 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. The K group did not reduce metabolic cost during adaptation. The U group reduced metabolic cost during adaptation to a cost 12% lower than the K group. We observed a significant effect of Time×Group (p<0.050) on step lengths and work by the right/slow leg during adaptation and post-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 occurs through a combination of biomechanical changes small in magnitude and a marked influence of non-biomechanical factors.