Motor learning of a novel dynamic coordination task in the lower-limb of young healthy adults

Understanding motor learning processes provides crucial insights into how individuals can recover function after neurological injury. While current research has advanced the understanding of motor learning in the upper limbs, exploration in the lower limb remains limited. This study aimed to elicit and quantify motor learning, skill retention and transfer, and aftereffects in lower-limb movements made by healthy young adults using a haptic robot. Participants interacted with a rotational spring-mass-damper virtual environment, learning to stabilize a virtual inertia disk at a target angular position with leg reaching movements. Baseline reaching and initial skill acquisition occurred on the first day. Skill retention was assessed after 22-48 h and inter-limb transfer was assessed by switching the leading leg. Aftereffects were measured by disabling the environment at the end of day two. Participants learned the novel task with their legs, reducing settling time and path length by 43 % and 48 %, by the end of day one. Retention was observed with a 40 % and 42 % reduction in settling time and path length at the start of the retention phase compared to beginning of initial acquisition. Inter-limb transfer resulted in a 43 % and 52 % decrease in settling time and path length at the start of the transfer phase. Lastly, aftereffects were detected, requiring washout to de-adapt to nominal movement with no environment. These findings suggest that lower-limb motor learning exhibits similar principles to upper-limb motor learning. Future work will study specific motor learning processes, like reinforcement learning, in the lower limbs and inform rehabilitation techniques.