Long-Range Correlations in Stride Intervals May Emerge from Non-Chaotic Walking Dynamics

Ahn, Jooeun; Hogan, Neville

doi:10.1371/journal.pone.0073239

Cited by 34 publications

(34 citation statements)

References 39 publications

(91 reference statements)

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“…Fourteen subjects [5 females, 9 males; mean age = 18.7 (18)(19)(20)(21) years] participated in experiment 1, 18 subjects [7 females, 11 males; mean age = 19.1 (18)(19)(20)(21) years] participated in experiment 2, and 12 subjects [5 females, 7 males; mean age = 20.0 (18)(19)(20)(21)(22) years] participated in experiment 3. Data from two subjects in experiment 1 were excluded because their average stepping accuracy across all conditions was more than 2 SDs from the mean.…”

Section: Methodsmentioning

confidence: 99%

“…As such, a small forward perturbation applied to the COM at midstep increases the speed of the COM, which in turn increases the collision loss so the additional energy that is injected into the system by the perturbation will be dissipated at collision (15). Although the basin of attraction for bipedal gait may be relatively shallow, spinal-level reflex pathways (3) may serve to facilitate gait-restorative responses that take advantage of this passive stability (18)(19)(20). † Active Control of Walking These insights imply that certain desirable characteristics of movement, such as coordination, efficiency, and stability, can emerge without active (i.e., perceptually guided) control.…”

Section: Significancementioning

confidence: 99%

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The critical phase for visual control of human walking over complex terrain

Matthis

Barton

Fajen

2017

Proc. Natl. Acad. Sci. U.S.A.

103

104

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To walk efficiently over complex terrain, humans must use vision to tailor their gait to the upcoming ground surface without interfering with the exploitation of passive mechanical forces. We propose that walkers use visual information to initialize the mechanical state of the body before the beginning of each step so the resulting ballistic trajectory of the walker's center-of-mass will facilitate stepping on target footholds. Using a precision stepping task and synchronizing target visibility to the gait cycle, we empirically validated two predictions derived from this strategy: (1) Walkers must have information about upcoming footholds during the second half of the preceding step, and (2) foot placement is guided by information about the position of the target foothold relative to the preceding base of support. We conclude that active and passive modes of control work synergistically to allow walkers to negotiate complex terrain with efficiency, stability, and precision.H umans and other animals are remarkable in their ability to take advantage of what is freely available in the environment to the benefit of efficiency, stability, and coordination in movement. This opportunism can take on at least two forms, both of which are evident in human locomotion over complex terrain: (i) harnessing external forces to minimize the need for self-generated (i.e., muscular) forces (1), and (ii) taking advantage of passive stability to simplify the control of a complex movement (e.g., ref. 2). In the ensuing section, we explain how walkers exploit external forces and passive stability while walking over flat, obstacle-free terrain.* We then generalize this account to walking over irregular surfaces by explaining how walkers can adapt gait to terrain variations while still reaping the benefits of the available mechanical forces and inherent stability. This account leads to hypotheses about how and when walkers use visual information about the upcoming terrain and where that information is found. We derive several predictions from these hypotheses and then put them to the test in three experiments. Passive Control in Human WalkingThe basic movement pattern of the human gait cycle arises primarily from the phasic activation of flexor and extensor muscle groups by spinal-level central pattern generators, regulated by sensory signals from lower limb proprioceptors and cutaneous feedback from the plantar surface of the foot. This low-level neuromuscular circuitry serves to maintain the rhythmic physical oscillations that define locomotor behavior (see ref. 3 for review). This section will provide an overview of the basic biomechanics of the bipedal gait cycle to show how these inherent physical dynamics contribute to the passive stability and energetic efficiency of human locomotion.During the single support phase of the bipedal gait cycle, when only one foot is in contact with the ground, a walker shares the physical dynamics of an inverted pendulum. The body's center of mass (COM) acts as the bob of the pendulum and is support...

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Section: Methodsmentioning

confidence: 99%

Section: Significancementioning

confidence: 99%

The critical phase for visual control of human walking over complex terrain

Matthis

Barton

Fajen

2017

Proc. Natl. Acad. Sci. U.S.A.

103

104

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“…The limited number of ARMA parameters contradicts conclusions in [17] and recently in [1]. These studies showed a stride intervals of normal human walking which exhibit long-range temporal correlations.…”

Section: Estimatormentioning

confidence: 73%

Huberian approach for reduced order ARMA modeling of neurodegenerative disorder signal

2015

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International audienceThe purpose of this paper is to address the question of the existence of auto regressive moving average (ARMA) models with reduced order for neurodegenerative disorder signals by using Huberian approach. Since gait rhythm dynamics between Parkinson's disease (PD) or Huntington's disease (HD) and healthy control (CO) differ, and since the stride interval presents great variability, we propose a different ARMA modeling approach based on a Huberian function to assess parameters. Huberian function as a mixture of L 2 and L 1 norms, tuned with a threshold γ from a new curve, is chosen to deal with stride signal disorders. The choice of γ is crucial to ensure a good treatment of NO and allows to reduce the model order. The disorders induce disturbances in the classical estimation methods and increase of the number of parameters of the ARMA model. Here, the use of the Huberian function reduces the number of parameters of the estimated models leading to a disease transfer function with low order for PD and HD. Mathematical approach is discussed and experimental results based on a database containing 16 CO, 15 PD, and 19 HD are presented

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“…Interestingly, adding variability decreases the average walking speed for a symmetric healthy model (Table III, [46]) but has little to no effect on the average walking speed for the asymmetric amputee model. Since one of the major causes of the reduced speed for healthy gait is likely reduced stance ankle work, the consistent prosthesis ankle work combined with a natural persistence of temporal perturbations [50] may be enough to prevent a reduction in speed for the human-prosthesis system.…”

Section: Simulationmentioning

confidence: 99%

Stable, Robust Hybrid Zero Dynamics Control of Powered Lower-Limb Prostheses

Martin

Gregg²

2017

IEEE Trans. Automat. Contr.

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To improve the quality of life for lower-limb amputees, powered prostheses are being developed. Advanced control schemes from the field of bipedal robots, such as hybrid zero dynamics (HZD), may provide great performance. HZD-based control specifies the motion of the actuated joints using output functions to be zeroed, and the required torques are calculated using input-output linearization. For one-step periodic gaits, there is an analytic metric of stability. To apply HZD-based control on a powered prosthesis, several modifications must be made. Because the prosthesis and amputee are only connected via the socket, the prosthesis controller does not have access to the full state of the biped, which decentralizes the form of the input-output linearization. The differences between the amputated and contralateral sides result in a two-step periodic gait, which requires the orbital stability metric to be extended. In addition, because human gait is variable, the prosthesis controller must be robust to continuous moderate perturbations. This robustness is proved using local input-to-state stability and demonstrated with simulations of an above-knee amputee model.

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Long-Range Correlations in Stride Intervals May Emerge from Non-Chaotic Walking Dynamics

Cited by 34 publications

References 39 publications

The critical phase for visual control of human walking over complex terrain

The critical phase for visual control of human walking over complex terrain

Huberian approach for reduced order ARMA modeling of neurodegenerative disorder signal

Stable, Robust Hybrid Zero Dynamics Control of Powered Lower-Limb Prostheses

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