The role of effort in adaptation to split-belt locomotion

In many motor learning tasks, the process of error reduction is mirrored in a process of effort reduction, where metabolic cost and or muscle co-contraction decrease gradually in tandem with error. Effort reduction may be incidental to the learning process, but high error movements can be more effortful and a drive to minimize effort costs could also play a role in motor learning. In this study, we focused on the effort requirements of the task, asking whether task (background) effort cost affects learning, aftereffects, or relearning in a split-belt walking task. We hypothesized that greater effort costs would amplify the need to reduce effort and accelerate learning. Alternatively, we hypothesized that greater effort requirement could compromise and slow the learning process. Participants in high, low, and control effort groups completed a split-belt walking task while wearing a weighted vest with 15% body mass, 5% body mass, or the vest only, and we assessed step length asymmetry throughout the protocol. Step length asymmetry changed similarly between groups, with similar rates and extent of learning and relearning and similar patterns of aftereffects when the split-belt perturbation was removed. We found no significant effect of task effort on the process of split-belt adaptation, suggesting that the brains response to gait asymmetry and ability to adapt to novel dynamics is relatively unchanged by background effort requirements of the task. NEW & NOTEWORTHYDespite the brains sensitivity to effort cost and willingness to adjust gait parameters to minimize cost, the process of split-belt adaptation was unaffected by increased effort requirements. This finding provides a foundation for further research into performance-dependent effort cost. Additionally, modest increases in effort should be further explored in rehabilitation applications where higher effort requirements may help build strength and fitness without impairing motor learning.