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February 2018

February 2018

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Authors:

Alessandro Santuz

Max-Delbrück-Centrum für Molekulare Medizin

Antonis Ekizos

Olympic Training Center of Berlin

Nils Eckardt

Leibniz Universität Hannover

Armin Kibele

Institute for Sports and Sport Science, University of Kassel

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Challenging human locomotion: Stability and modular organisation in unsteady conditions

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February 2018

Alessandro Santuz · Antonis Ekizos · Nils Eckardt · Armin Kibele · Adamantios Arampatzis

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KINEMATIC STRATEGIES TO KEEP AN UNCHANGED MARGIN OF STABILITY DURING TREADMILL RUNNING ON AN EVEN AN...

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Understanding how to control stability when running, particularly when being exposed to uneven terrain, is vital to prevent falls and to get an insight into compensatory strategies while running on uneven terrain. The purpose of this study was to assess surface related differences of the margin of stability, kinematics of hip and knee and upper body acceleration which may affect the control of ... [Show full abstract] running stability. Eighteen healthy younger adults ran on an even and an uneven surfaced treadmill for two minutes at fixed speeds of 2.0 m/s (female) and 2.2 m/s (male), respectively. Results showed an unchanged margin of stability in both conditions. Further, lower limb kinematics, step width variability and upper body acceleration increased on the uneven surface meaningfully to keep the extrapolated centre of mass within the base of support.

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Challenging human locomotion: Stability and modular organisation in unsteady conditions

February 2018 · Scientific Reports

The need to move over uneven terrain is a daily challenge. In order to face unexpected perturbations due to changes in the morphology of the terrain, the central nervous system must flexibly modify its control strategies. We analysed the local dynamic stability and the modular organisation of muscle activation (muscle synergies) during walking and running on an even- and an uneven-surface ... [Show full abstract] treadmill. We hypothesized a reduced stability during uneven-surface locomotion and a reorganisation of the modular control. We found a decreased stability when switching from even- to uneven-surface locomotion (p < 0.001 in walking, p = 0.001 in running). Moreover, we observed a substantial modification of the time-dependent muscle activation patterns (motor primitives) despite a general conservation of the time-independent coefficients (motor modules). The motor primitives were considerably wider in the uneven-surface condition. Specifically, the widening was significant in both the early (+40.5%, p < 0.001) and late swing (+7.7%, p = 0.040) phase in walking and in the weight acceptance (+13.6%, p = 0.006) and propulsion (+6.0%, p = 0.041) phase in running. This widening highlighted an increased motor output's robustness (i.e. ability to cope with errors) when dealing with the unexpected perturbations. Our results confirmed the hypothesis that humans adjust their motor control strategies' timing to deal with unsteady locomotion.

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Challenging human locomotion: stability and modular organisation in unsteady conditions

July 2018

In our daily life, we regularly walk and run in complex environments. To deal with unexpected perturbations, the central nervous system must adaptively modify its control strategies. However, the continuous integration of sensory and motor information likely undergoes some simplification for achieving precise control, possibly by activating muscles in modular patterns called synergies 1. With ... [Show full abstract] this study, we aimed to improve our understanding of the mechanisms underlying the neuromuscular control of human unsteady locomotion by investigating walking and running on an even-and an uneven-surface treadmill. We hypothesized a reduction in stability and a reorganisation of the modular control in uneven-compared to even-surface locomotion. We had 18 healthy, young adults (7 female, 11 male) walking and running on an even-and an uneven-surface treadmill. Using nonlinear time series analysis to calculate the maximum Lyapunov exponent, we assessed the local dynamic stability 2 and extracted muscle synergies with the help of non-negative matrix factorisation 3. We found a decreased stability when switching from even-to uneven-surface locomotion (p<0.001 walking, p=0.001 running). We observed a substantial modification of the time-dependent muscle activation patterns (motor primitives) despite a general conservation of the time-independent coefficients (motor modules). The motor primitives were wider in the uneven-surface condition. The widening was significant in the early (+40.5%, p<0.001) and late swing (+7.7%, p=0.040) phase in walking and in the weight acceptance (+13.6%, p=0.006) and propulsion (+6.0%, p=0.041) phase in running. The widening highlighted an alteration in the motor output's temporal structure, evidencing an increased robustness to overcome continuous perturbations. During running, mechanical effects are likely the predominant motor controllers 4. In walking, though, proprioceptive sensory feedback could provide superior contribution due to the slower speed 4. In the stance phase of perturbed running, contextual anticipations might have forced the system to mainly rely on the intrinsic mechanical response. Conversely, during the swing phase of perturbed walking, the robuster swinging leg's neuromuscular control was achieved during the contralateral limb's proprioceptive sensory reinforcement. These findings confirmed our hypotheses and demonstrated the use of a consistent set of neural control elements during perturbed locomotion, with modifications of the basic activation patterns. This indicated a transfer from a refined to a more robust control in the presence of continuously variable perturbations, with possible differences in the utilisation of proprioceptive sensory feedback between walking and running.

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Challenging human locomotion: stability and modular organisation in unsteady conditions

February 2018

The need to move over uneven terrain is a daily challenge. In order to face unexpected perturbations due to changes in the morphology of the terrain, the central nervous system must flexibly modify its control strategies. We analysed the local dynamic stability and the modular organisation of muscle activation (muscle synergies) during walking and running on an even- and an uneven-surface ... [Show full abstract] treadmill. We hypothesized a reduced stability during uneven-surface locomotion and a reorganisation of the modular control. We found a decreased stability when switching from even- to uneven-surface locomotion (p < 0.001 in walking, p = 0.001 in running). Moreover, we observed a substantial modification of the time-dependent muscle activation patterns (motor primitives) despite a general conservation of the time-independent coefficients (motor modules). The motor primitives were considerably wider in the uneven-surface condition. Specifically, the widening was significant in both the early (+40.5%, p < 0.001) and late swing (+7.7%, p = 0.040) phase in walking and in the weight acceptance (+13.6%, p = 0.006) and propulsion (+6.0%, p = 0.041) phase in running. This widening highlighted an increased motor output’s robustness (i.e. ability to cope with errors) when dealing with the unexpected perturbations. Our results confirmed the hypothesis that humans adjust their motor control strategies’ timing to deal with unsteady locomotion.

View full-text

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