Adaptation of Step-to-Step Mechanical Work on Center of Mass during Split-belt Treadmill Walking
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The neuromechanical goal of locomotor adaptation in healthy human walking is largely unknown. Understanding how locomotor adaptation is achieved in the context of such a goal provides insight into gait deficits following musculoskeletal or neuromuscular impairment. The dynamic walking theory presents a mechanistic framework for legged locomotion using passive dynamics. Applying the theory to human gait. collision loss at heel strike is the greatest source of energy loss. In order to reduce collision loss. or negative mechanical work. the trail limb produces a pre-emptive impulse just before lead limb heel strike. increasing positive mechanical work. The dynamic walking theory has not yet been applied to locomotor adaptation. This project investigates the neuromechanical goal of locomotor adaptation through a dynamic walking approach. With two belts running at different speeds. the split-belt treadmill presents a unique environment has been used as an effective tool for examining adaptation. Consistent with the dynamic walking approach. we hypothesized that there would be a reduction of negative mechanical work on the center of mass coupled with an increase in positive work from early to late adaptation. Fourteen healthy young adults were asked to walk on a split-belt treadmill with both belts moving at the same speed (''tied'' condition) or at different speeds ("split-belt" condition). Baseline trials consisted of three different tied conditions with belts running at slow. middle. and fast speeds. The adaptation period involved subjects walking in the split-belt condition for ten minutes with one belt set at the slow speed and the other at the fast speed. Finally. subjects walked on the slow tied condition for the post-adaptation period. Ground reaction forces provided by AMTI force plates were imported to Matlab for analysis and calculation of mechanical work. The step-to-step work calculations were then categorized into two different step transitions: fast to slow and slow to fast. The fast to slow step transition indicate steps where the subjects' trail limb is on the fast belt and the lead limb is on the slow belt. Results show a significant reduction of negative work in addition to an increase in positive work for the fast to slow step transitions. while the slow to fast step transitions do not show significance. Results from this work offer insight into the neuromechanical goals of locomotion. This has implications for the development of targeted gait rehabilitation and evidence-based outcome measures.