Variability of Practice and its Application to Locomotor Adaptation
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Asymmetric gait, or a difference in functioning between legs during human locomotion, is a health concern that can lead to secondary complications such as chronic musculoskeletal injury or a more sedentary lifestyle. Restoration of gait symmetry requires a gait adaptation, or a change in the way that an individual walks. Further knowledge of how to best promote a gait adaptation could lead to the creation of future rehabilitative protocols geared towards restoration of symmetric gait. To address this, a variable practice paradigm was implemented in able-bodied individuals walking asymmetrically on a split-belt treadmill. Individuals were assigned into one of three practice groups (from least variable to most: serial, random blocked, random) and walked on the treadmill for 720 strides of motor skill acquisition according to their given paradigm. They were asked to return 24 hours later and were given one of two tests for motor learning: retention or transfer. Three-dimensional kinematic and kinetic data were collected throughout the experimental protocol and used to analyze walking performance between the three practice groups. Results indicated that random blocked practice resulted in the best retention and transfer of mediolateral balance control variability, while serial practice had the highest variability on the transfer test. It was further demonstrated that this paradigm resulted in a unique mechanical strategy implemented by each practice group that further describes the role of variable practice in gait adaptation: random practice during acquisition, random blocked during retention, and serial during transfer. A principal component analysis showed that variable practice also results in the adoption of specific coordinative structuring of joint and segmental kinematics. These structures were mostly different across practice groups during the acquisition and retention phases. While it was generally hypothesized that random practice, which induces the highest amount of stepping errors during acquisition, would result in the best retention and transfer of the adapted gait pattern, this practice group did not perform as well as expected on the measured outcomes. Random blocked practice, on the other hand, may provide the optimal level of challenge and variability to best facilitate a gait adaptation. This dissertation includes previously published and unpublished co-authored material.