Using asymmetry to your advantage: learning to acquire and accept external assistance during prolonged split-belt walking

People often adapt their coordination patterns during walking to reduce energy cost by using sources of external assistance in the environment. Adaptation to walking on a split-belt treadmill, where one belt moves faster than the other, provides an opportunity for people to acquire positive work from the treadmill to reduce metabolic cost by modifying where they step on the faster belt. Though we know what people should do to acquire this assistance, this strategy is not observed during typical adaptation studies. Here, by extending the duration of adaptation, we show that people continuously optimize energetic cost by adjusting foot placement to acquire positive work from the treadmill and reduce the work performed by the legs. These results demonstrate that learning to acquire and take advantage of assistance to reduce energetic cost is central in shaping adaptive locomotion, but this process occurs over timescales longer than those used in typical studies.