A Gradual vs. Sudden Introduction to Novel Locomotor Task Requirements: Consequences for Motor Learning, Balance Control and Cognitive Demand

The physical rehabilitation of individuals with lower limb loss has traditionally been guided by a device driven paradigm, with much less attention, if any, allocated to the manner in which established motor learning strategies may be used to learn prosthetic locomotor skills. Much of this gap is attributable to the fact that the efficacy of most motor learning strategies has been derived from constrained upper extremity motor skills. Motor learning strategies that increase practice difficulty and the size of movement errors are thought to facilitate motor learning. In contrast to this, gradual training minimizes movement errors and reduces practice difficulty by incrementally introducing task requirements, yet remains as effective as sudden training and its large movement errors for learning novel reaching tasks. While attractive as a locomotor rehabilitation strategy, it remains unknown whether the efficacy of gradual training extends to learning locomotor tasks and their unique functional requirements. Therefore, a series of experiments were designed to examine whether gradual versus sudden training influenced the acquisition of task specific dynamics, the maintenance of lateral balance control and the cognitive demand required among unimpaired adults during training as well as 24 hour retention and transfer performance of a novel locomotor task, asymmetric split belt treadmill walking. The potential clinical application of this work was then examined by studying the ability of individuals with transtibial limb loss to use a novel powered prosthetic foot based upon either a gradual or sudden restoration of propulsive ankle power. Despite more specific and difficult practice for the sudden cohort, gradual training preserved motor learning of the novel locomotor task, reduced the challenge to lateral balance control and altered the whole-body kinematic strategy selected to regulate lateral balance while reducing the cognitive demand required during training. This suggests that large movement errors and increased practice difficulty may not be necessary for learning locomotor tasks, and that gradual training may present a viable locomotor rehabilitation strategy. Indeed, among a small cohort of individuals with unilateral transtibial limb loss, a gradual restoration of propulsive ankle power was found to promote more consistent elicitation of prosthetic peak ankle power.