Energetics and Biomechanics of Uneven Walking for Young and Older Adults
Creators: name: Hosseini Yazdi, Seyed Saleh
Publisher: name: Graduate Studies
Year: 2024
Subjects: subject: Uneven walking
subject: walking energetics
subject: gait parameters
subject: step mechanical work
subject: Engineering--Biomedical

description: Humans walk on various surfaces, expending considerable energy in the process. The biomechanics and energetics of walking suggest that humans adjust and select gait variables to optimize energy economy, as evidenced by experiments on even terrain. However, natural terrains are often complex, requiring significantly more energy for walking. Nevertheless, most biomechanical researches and experimental methods have focused on even terrain, necessitating a more quantitative understanding of biomechanical adjustments on complex terrains and their relation to energy expenditure. Therefore, new approaches are needed to understand better how humans walk on uneven terrains as a subset of complex terrains. Consequently, the initial goal of this study was to develop laboratory equipment to evaluate human adjustments during uneven walking while controlling other study parameters. Accordingly, an instrumented treadmill was structurally modified to accommodate uneven terrains. Subsequently, three uneven terrains with different amplitudes (peak-to-peak heights) were fabricated to examine the influence of increased terrain amplitude. Limb-by-limb ground reaction forces were measured while collecting energetics and motion capture data, with age, state of lookahead, and walking speed as controlled parameters. With the normal lookahead, it was observed that humans made anticipatory adjustments perhaps to minimize the total walking mechanical work over the course of walking. The average mechanical work increased proportionally with the cube of walking velocity, the square of terrain amplitude, restricted lookahead, and age, as did walking step variabilities, indicating active walking corrections. Terrain amplitudes altered the relative timing of active work (push-off) and subsequent walking dissipation (collision), known as push-off lead time. Push-off lead time varied with age and restricted lookahead, with the preferred order of push-off and collision reversed in some instances. This aligned with the hypothesis that timing disruptions increase active work during mid-flight, corresponding to previously reported uneven walking redistribution of joint powers from distal to proximal. Older adults exhibited differences from young adults in walking patterns. While feedback control (applied with restricted lookahead) resembled that of young adults, anticipatory (feedforward) control appeared poor, consistent with older adults' tendency to use passive control strategies such as wider steps. Compared to young adults, the excess positive work of older adults was speculated to be associated with higher soft tissue dissipations. I observed that metabolic energy varied in proportion to step mechanical work. Walking energetics in older adults increased at higher rates with the interaction of age and rising terrain amplitude, similar to step mechanical work. Therefore, the decline in muscle delta efficiency across terrains might be associated with this interaction. Step mechanical work also explained most of the energetics of walking, as evidenced by the regression analysis coefficient of determination. The fraction of energetics not explained by step work was likely due to peripheral work, continuous corrections reflected as variabilities, deviations from nominal walking, muscle coactivation, posture maintenance, and other factors. Overall, I could quantify the walking energetics variations with age, state of lookahead, and terrain amplitude and explore the mechanical determinants associated with the parameters of interest. It exhibited increased positive work performance that is physiologically expensive, aligned with the metabolic rate changes.