The broad, long-term objectives of this proposal are to quantitatively characterize, compare, and simulate the use of task space control in normal and pathological gait due to lower limb amputation. Extensive research has detailed joint kinematics and kinetics of human locomotion and movement control with normal and various motor function disorders. Yet, relatively little is known about how humans relate joint-level information to higher-level locomotor goals. Understanding basic biomechanical tenets governing leg control before and after injury will provide a general theoretical framework for creating new therapeutic interventions for pathological gait disabilities. This project proposes to use behavioral locomotion experiments to study task space control in both healthy intact human subjects and in both Below-Knee (transtibial) and Above-Knee (transfemoral) amputees walking on prosthetic legs. This project will use extensive data analysis to quantify and characterize task space control during locomotion using variables identified from biomechanical models and by eigenanalysis. Based on the analytical results, a further study will create a physics-based computer simulation of pathological amputee gait with corrective joint torques computed from the differences discovered between normal and amputee gait. The general hypothesis of the project is that humans control locomotion by precisely guiding their legs through a predefined task space while allowing flexibility in joint-level dynamics and that more proximal limb amputations will result in greater losses in this ability to exploit task space redundancy.
Three specific aims to study the use of task space control during locomotion are addressed: normal human locomotion (Aim1);pathological gait due to lower limb amputation (Aim2);and, the evaluation and simulation of the changes from normal to pathological human walking (Aim3). Achieving these three aims will provide immediate deliverables by quantifying functionally relevant task variables for normal human gait and a theoretical understanding of how these control variables change after a neuromechanical pathology such as lower limb amputation. This work will develop new analytical tools to quantitatively assay normal and amputee gait, however, it will also be generally applicable to the study of all gait pathologies. It could further impact future therapeutic approaches for gait rehabilitation that use task-level rather than joint-level rehabilitation goals and inspire control systems for the rapidly growing field of rehabilitative robotic devices. The proposed work will also form a theoretical framework for future studies of the neural mechanisms underlying leg control during locomotion.

Public Health Relevance

Nearly all diseases that affect our muscles, bones, and nerves have the potential to affect our ability to walk normally, which is critical to our independence and quality of life. This project combines exciting new physics-based computer simulation techniques with biomechanical experiments on humans to learn how motor redundancy in the legs is exploited to generate precise repetitive movements and how this control strategy is compromised by lower limb amputation. This work will generate new analytical tools to understand how normal and pathological gait due to lower limb amputation is controlled and restored, but will have broad implications for the treatment of all gait disorders.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Motor Function, Speech and Rehabilitation Study Section (MFSR)
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Chen, Daofen
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Georgia Institute of Technology
Schools of Arts and Sciences
United States
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Selgrade, Brian P; Toney, Megan E; Chang, Young-Hui (2017) Two biomechanical strategies for locomotor adaptation to split-belt treadmill walking in subjects with and without transtibial amputation. J Biomech 53:136-143
Selgrade, Brian P; Thajchayapong, Montakan; Lee, Gloria E et al. (2017) Changes in mechanical work during neural adaptation to asymmetric locomotion. J Exp Biol 220:2993-3000
Toney, Megan E; Chang, Young-Hui (2016) The motor and the brake of the trailing leg in human walking: leg force control through ankle modulation and knee covariance. Exp Brain Res 234:3011-23
Giest, Tracy N; Chang, Young-Hui (2016) Biomechanics of the human walk-to-run gait transition in persons with unilateral transtibial amputation. J Biomech 49:1757-1764
Auyang, Arick G; Chang, Young-Hui (2013) Effects of a foot placement constraint on use of motor equivalence during human hopping. PLoS One 8:e69429
Toney, Megan E; Chang, Young-Hui (2013) Humans robustly adhere to dynamic walking principles by harnessing motor abundance to control forces. Exp Brain Res 231:433-43