How a person walks, or their gait strategy, has substantial ties to their ability to function in society. Gait strategies are formed by the contributions of each lower extremity constituent (i.e., hips, knees, ankles, and feet) to the walking pattern. The formation of a gait strategy is dependent on several factors (purpose, environment, and physical health), of which each has a spectrum of conditions (e.g., speed, terrain, muscle weakness, etc.). Understanding the rules by which individuals adapt gait strategies to accommodate a spectrum of conditions is useful for informing assistive device design and rehabilitation protocols that help individuals reach their highest levels of function. Recognizing the relationship between changes in mechanical energetics (work and energy) and movement, energetics variables are well suited to be quantitative summary metrics that characterize gait strategy adaptations.

The overall purpose of this dissertation was to develop and apply a general framework to explore the energetics of gait strategy adaptations. Two novel approaches using mechanical energetics were developed to create the Gait Energetics Adaptations Resource (GEAR) framework. The Constituent Lower Extremity Work (CLEW) approach represents the proportion of constituent lower extremity work contributing to the absolute work done over a time interval – such as a gait cycle. Then, the Work-Energy Profiles approach was developed using the workenergy relationship to examine the mechanical energetics of gait strategies within and between a set of conditions.

These two approaches were developed by quantifying the gait strategy adaptations that occur when typical, unimpaired individuals walk at slow, moderate, and typical speeds. The CLEW approach revealed that the relative ankle and foot work adapt by increasing from slow to typical walking speeds while the relative hip and knee work remain constant across speeds. The Work-Energy Profiles approach revealed that the gait strategy implemented at a slow speed uses more pendular mechanics to raise the center of mass compared to the other speeds, while the strategy at a typical speed is more effective at “propelling” the body into its next step compared to the other speeds.

An application of the GEAR framework was conducted by quantifying the gait strategy adaptations that occur when a cohort of unimpaired individuals walked with and without an artificial ankle impairment unilaterally and bilaterally. The CLEW approach revealed that the knee compensates during stance when the stance limb ankle is partially impaired unilaterally, but that the hip and knee both compensate when ankles are impaired bilaterally. The Work-Energy Profiles demonstrated that the compensatory strategies with both unilateral and bilateral ankle impairment are effective in propelling the body during double support phase compared with no ankle impairment, but the compensatory strategies are less effective during single support.

The CLEW and Work-Energy Profiles approaches under the GEAR framework are the first methodologies to use comprehensive energetics metrics for the quantification of gait strategy adaptations and their effectiveness. The GEAR framework will be used in the future to explore gait adaptations across the spectra of many different conditions that can be helpful in fully understanding the underlying rules and mechanisms by which humans adapt their gait strategies.