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Transients, Variability, Stability and Energy in Human Locomotion

Seethapathi, Nidhi, Seethapathi

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Mechanical Engineering.
Most research in human locomotion is limited to steady-state, constant speed and symmetric locomotion behaviors. However, walking and running in everyday life requires us to adapt our locomotion strategies to intrinsic noise-like transients, external environmental irregularities and more general practical demands on moving from place-to-place. Here, we investigate such locomotion behaviors in three broadly related studies: (I) the dynamics of walking with changing speeds, (II) control strategies for running stably in the presence of noise-like deviations, and (III) the dynamics of different types of asymmetric walking. In part I, we measured the metabolic cost of walking with changing speeds by having subjects speed up and slow down on a constant speed treadmill. We find that the metabolic cost of changing speeds when walking is significant and can constitute 8 to 20% of our daily walking energy budget. We explain the incremental cost with simple mathematical models, correlating the cost with increased mechanical work. Moreover, this increased metabolic cost predicts lower preferred walking speeds of humans walking short distances, which we confirmed by further experiments on non-amputee and amputee subjects. In part II, we reveal the control strategies hidden within the step-to-step variability in steady-state human running data, adopted by humans in order to run stably in the presence of unavoidable and intrinsically generated sensorimotor errors. The stabilizing control is largely implemented when the leg is on the ground and is well-predicted by deviations in the center-of-mass states during the previous flight phase. We show that humans use almost-deadbeat control of horizontal velocity deviations; killing about 70-100% of horizontal velocity deviations within one step by appropriately modulating the placement of the foot and the force applied on the ground by the leg. Further, deviations in the center-of-mass motion predicts the swing foot placement before the swing foot itself. On implementing these strategies on two simple computational biped models, we find that the models can withstand deviations up to ten times larger than the step-to-step variability from which they were inferred. This suggests that the control strategies humans use for small intrinsic errors can be extended to deal with larger external perturbations. In part III, we predict the steady-state adaptation behaviors in humans constrained to walk asymmetrically. The constraints are in the form of asymmetric masses and asymmetric belt speeds. We conduct metabolic energy optimization of simple biped models, making changes in the dynamics of the model corresponding to each type of asymmetry. We find that the optimization-based predictive models agree with trends in the stance time asymmetry observed in experiments for the asymmetric mass and asymmetric belt speed conditions. For split-belt walking, the optimization-based model predicts that humans will adapt to taking longer steps on the fast belt and shorter steps on the slow belt. This qualitative prediction made by the model matches with behavior that has been observed by other researchers over many days of adaptation to the new paradigm.
Manoj Srinivasan (Advisor)
Alison Sheets-Singer (Committee Member)
Giorgio Rizzoni (Committee Member)
Martin Golubitsky (Committee Member)
Rama Krishna Yedavalli (Committee Member)
153 p.

Recommended Citations

Citations

  • Seethapathi, Seethapathi, N. (2018). Transients, Variability, Stability and Energy in Human Locomotion [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1534590933898397

    APA Style (7th edition)

  • Seethapathi, Seethapathi, Nidhi. Transients, Variability, Stability and Energy in Human Locomotion. 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1534590933898397.

    MLA Style (8th edition)

  • Seethapathi, Seethapathi, Nidhi. "Transients, Variability, Stability and Energy in Human Locomotion." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1534590933898397

    Chicago Manual of Style (17th edition)