American Society of Biomechanics Journal of Biomechanics Award 2018: Adaptive motor planning of center-of-mass trajectory during goal-directed walking in novel environments

Bucklin, Mary; Mengnan,; Wu, Mengnan; Brown, Geoffrey L.; Gordon, Keith E.

doi:10.1016/j.jbiomech.2019.07.030

“…The COM lateral offset is an anticipatory postural adjustment that during a typical gait initiation is used to shift the COM location laterally to unweight the stepping limb 31 . In our prior study 30 we found that participants adapted the magnitude of their COM lateral offset in the opposite direction of a predictable and consistent laterally-directed force field. The effect of this action preemptively positioned the COM location to counter the effects of the force field once the forward walking trajectory begins.…”

Section: Discussionmentioning

confidence: 84%

Optimism Persists when Walking in Unpredictable Environments

Bucklin¹,

Deol

²

,

Brown³

et al. 2022

Preprint

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Humans continuously modulate their control strategies during walking based on their ability to anticipate disturbances. However, how people adapt and use motor plans to create stable walking in unpredictable environments is not well understood. Our purpose was to investigate how people adapt motor plans when walking in a novel and unpredictable environment. We evaluated the whole-body center of mass (COM) trajectory of participants as they performed repetitions of a discrete goal-directed walking task during which a laterally-directed force field was applied to the COM. The force field was proportional in magnitude to forward walking velocity and randomly directed towards either the right or left each trial. We hypothesized that people would adapt a control strategy to reduce the COM lateral deviations created by the unpredictable force field. In support of our hypothesis, we found that with practice the magnitude of COM lateral deviation was reduced by 28% (left) and 44% (right). Participants adapted two distinct unilateral strategies that collectively created a bilateral resistance to the unpredictable force field. These strategies included an anticipatory postural adjustment to resist against forces applied to the left, and a more lateral first step to resist against forces applied to the right. In addition, during catch trials when the force field was unexpectedly removed, participants exhibited trajectories similar to baseline trials. These findings were consistent with an impedance control strategy that provides a robust resistance to unpredictable perturbations. However, we also found evidence that participants made predictive adaptations in response to their immediate experience that persisted for three trials. Due to the unpredictable nature of the force field, this predictive strategy would sometimes result in greater lateral deviations when the prediction was incorrect. The presence of these competing control strategies may have long term benefits by allowing the nervous system to identify the best overall control strategy to use in a novel environment.

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“…As this was our first attempt to quantify the effects of the movement amplification force fields on COM dynamics, we chose not to scale the force field gains for each participant. While there will probably be absolute differences in the resulting COM dynamics experienced between individuals with different body mass [31], we assumed that the two gains chosen were sufficient to test changes in control strategies and associated metabolic energy costs when walking in a low-and high-gain negative damping field.…”

Section: Experiments Protocol and Set-upmentioning

confidence: 99%

A novel Movement Amplification environment reveals effects of controlling lateral centre of mass motion on gait stability and metabolic cost

Wu

¹

,

Brown

²

,

Woodward

³

et al. 2020

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During human walking, the centre of mass (COM) laterally oscillates, regularly transitioning its position above the two alternating support limbs. To maintain upright forward-directed walking, lateral COM excursion should remain within the base of support, on average. As necessary, humans can modify COM motion through various methods, including foot placement. How the nervous system controls these oscillations and the costs associated with control are not fully understood. To examine how lateral COM motions are controlled, healthy participants walked in a ‘Movement Amplification’ force field that increased lateral COM momentum in a manner dependent on the participant's own motion (forces were applied to the pelvis proportional to and in the same direction as lateral COM velocity). We hypothesized that metabolic cost to control lateral COM motion would increase with the gain of the field. In the Movement Amplification field, participants were significantly less stable than during baseline walking. Stability significantly decreased as the field gain increased. Participants also modified gait patterns, including increasing step width, which increased the metabolic cost of transport as the field gain increased. These results support previous research suggesting that humans modulate foot placement to control lateral COM motion, incurring a metabolic cost.

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“…These include controlling stiffness via co-activation of antagonistic muscle pairs 8-10 , exploitation of posture [11][12][13][14] , and tuning of re ex gains 28,29 . In our previous research 30 ,we observed two postural control strategies that were particularly valuable for resisting strong laterally-directed external forces during goal directed walking (walking from a start to an end target). These strategies included modulating lateral foot placement of the stepping limb during walking and increasing the lateral translation of the COM during the anticipatory postural adjustment occurring during gait initiation.…”

Section: Introductionmentioning

confidence: 99%

“…The iterative experimental design allowed us to evaluate trial-by-trial adaptations while the application and removal of external forces will be used to investigate underlying control mechanisms 8-10 . We previously have found this experimental design valuable for understanding how people plan and control walking in novel and predictable environments 30 .…”

Section: Introductionmentioning

confidence: 99%

Optimism Persists when Walking in Unpredictable Environments

Bucklin¹,

Deol²,

Brown³

et al. 2022

Preprint

Self Cite

0

View full text Add to dashboard Cite

Humans continuously modulate their control strategies during walking based on their ability to anticipate disturbances. However, how people adapt and use motor plans to create stable walking in unpredictable environments is not well understood. Our purpose was to investigate how people adapt motor plans when walking in a novel and unpredictable environment. We evaluated the whole-body center of mass (COM) trajectory of participants as they performed repetitions of a discrete goal-directed walking task during which a laterally-directed force field was applied to the COM. The force field was proportional in magnitude to forward walking velocity and randomly directed towards either the right or left each trial. We hypothesized that people would adapt a control strategy to reduce the COM lateral deviations created by the unpredictable force field. In support of our hypothesis, we found that with practice the magnitude of COM lateral deviation was reduced by 28% (left) and 44% (right). Participants adapted two distinct unilateral strategies that collectively created a bilateral resistance to the unpredictable force field. These strategies included an anticipatory postural adjustment to resist against forces applied to the left, and a more lateral first step to resist against forces applied to the right. In addition, during catch trials when the force field was unexpectedly removed, participants exhibited trajectories similar to baseline trials. These findings were consistent with an impedance control strategy that provides a robust resistance to unpredictable perturbations. However, we also found evidence that participants made predictive adaptations in response to their immediate experience that persisted for three trials. Due to the unpredictable nature of the force field, this predictive strategy would sometimes result in greater lateral deviations when the prediction was incorrect. The presence of these competing control strategies may have long term benefits by allowing the nervous system to identify the best overall control strategy to use in a novel environment.

show abstract

American Society of Biomechanics Journal of Biomechanics Award 2018: Adaptive motor planning of center-of-mass trajectory during goal-directed walking in novel environments

Cited by 17 publications

References 49 publications

Optimism Persists when Walking in Unpredictable Environments

Optimism Persists when Walking in Unpredictable Environments

A novel Movement Amplification environment reveals effects of controlling lateral centre of mass motion on gait stability and metabolic cost

Optimism Persists when Walking in Unpredictable Environments

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