Using asymmetry to your advantage: learning to acquire and accept external assistance during prolonged split-belt walking

Sánchez, Natalia Martínez; Simha, Surabhi N.; Donelan, J. Maxwell; Finley, James M.

doi:10.1101/2020.04.04.025619

Cited by 8 publications

(17 citation statements)

References 50 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The aforementioned minimal biped model (Figure 4), when put through a split-belt adaptation protocol of Figure 1b — that is, equal belt speeds for a few minutes (baseline), then unequal speeds (adaptation phase), and then equal speeds again (deadaptation phase) — produces transients in walking asymmetry that are qualitatively identical to those found in experiment (Figure 5). Just like in the experiments, the step length asymmetry jumps to negative quickly at the beginning of adaptation and then slowly moves toward symmetry (zero) and then eventually positive asymmetry given enough time 14,17 or a fast enough learning rate. During de-adaptation, the step length asymmetry jumps to a more positive values and then slowly drifts back to zero.…”

Section: Resultssupporting

confidence: 55%

“…Specifically, when humans walk on a split-belt treadmill, they exhibit certain stereotypical changes in their left-right gait symmetry (Figure 1c-e), commonly characterized in the literature via the step length symmetry and the step time symmetry 8-11, 15, 16 . These symmetry changes are also accompanied by energy reductions over a longer period of time 12,14,17 , suggesting that the final adaptation may be driven in part by energy minimization 1,[18][19][20] .…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Exploration-based learning of a stabilizing controller predicts locomotor adaptation

Seethapathi

Clark

Srinivasan

2021

Preprint

View full text Add to dashboard Cite

Humans are able to adapt their locomotion to a variety of novel circumstances, for instance, walking on diverse terrain and walking with new footwear. During locomotor adaptation, humans have been shown to exhibit stereotypical changes in their movement patterns. Here, we provide a theoretical account of such locomotor adaptation, positing that the nervous system prioritizes stability in the short timescale and improves energy expenditure over a longer timescale. The resulting mathematical model has two processes: a stabilizing controller which is gradually changed by a reinforcement learner that exploits local gradients to lower energy expenditure, estimating gradients indirectly via intentional exploratory noise. We consider this model walking and adapting under three novel circumstances: walking on a split-belt treadmill (walking with each foot on a different belt, each belt at different speeds), walking with an exoskeleton, and walking with an asymmetric leg mass. This model predicts the short and long timescale changes observed in walking symmetry on the split-belt treadmill and while walking with the asymmetric mass. The model exhibits energy reductions with exoskeletal assistance, as well as entrainment to time-periodic assistance. We show that such exploration-based learning is degraded in the presence of large sensorimotor noise, providing a potential account for some impairments in learning.

show abstract

Section: Resultssupporting

confidence: 55%

Section: Introductionmentioning

confidence: 99%

Exploration-based learning of a stabilizing controller predicts locomotor adaptation

Seethapathi

Clark

Srinivasan

2021

Preprint

View full text Add to dashboard Cite

show abstract

“…Gait adaptation is commonly assessed on a split-belt treadmill (SBT), which has two independent belts. One measure of SBT gait that adapts is step length asymmetry [2][3][4][5]. Initially, healthy individuals walk on the SBT with asymmetric step lengths, where the leg on the slow belt takes a longer step than the leg on the fast belt [2].…”

Section: Introductionmentioning

confidence: 99%

“…Step length asymmetry gradually decreases over the course of ten minutes, despite the belts still moving at different speeds. Provided more than ten minutes to adapt, step lengths become asymmetric such that the fast leg takes a longer step than the slow leg [4] likely in response to the work done by treadmill on the legs [6][7][8]. Healthy individuals adjust their walking patterns on an SBT by adapting temporal (step timing) and spatial (step position) parameters when gait is perturbed [9,10].…”

Section: Introductionmentioning

confidence: 99%

Adapting gait with asymmetric visual feedback affects deadaptation but not adaptation in healthy young adults

2021

View full text Add to dashboard Cite

Split-belt treadmill walking allows researchers to understand how new gait patterns are acquired. Initially, the belts move at two different speeds, inducing asymmetric step lengths. As people adapt their gait on a split-belt treadmill, left and right step lengths become more symmetric over time. Upon returning to normal walking, step lengths become asymmetric in the opposite direction, indicating deadaptation. Then, upon re-exposure to the split belts, step length asymmetry is less than the asymmetry at the start of the initial exposure, indicating readaptation. Changes in step length symmetry are driven by changes in step timing and step position asymmetry. It is critical to understand what factors can promote step timing and position adaptation and therefore influence step length asymmetry. There is limited research regarding the role of visual feedback to improve gait adaptation. Using visual feedback to promote the adaptation of step timing or position may be useful of understanding temporal or spatial gait impairments. We measured gait adaptation, deadaptation, and readaptation in twenty-nine healthy young adults while they walked on a split-belt treadmill. One group received no feedback while adapting; one group received asymmetric real-time feedback about step timing while adapting; and the last group received asymmetric real-time feedback about step position while adapting. We measured step length difference (non-normalized asymmetry), step timing asymmetry, and step position asymmetry during adaptation, deadaptation, and readaptation on a split-belt treadmill. Regardless of feedback, participants adapted step length difference, indicating that walking with temporal or spatial visual feedback does not interfere with gait adaptation. Compared to the group that received no feedback, the group that received temporal feedback exhibited smaller early deadaptation step position asymmetry (p = 0.005). There was no effect of temporal or spatial feedback on step timing. The feedback groups adapted step timing and position similarly to walking without feedback. Future work should investigate whether asymmetric visual feedback also results in typical gait adaptation in populations with altered step timing or position control.

show abstract

“…However, motor learning can have an effect on metabolic rate during a novel task; as individuals learn a new task, metabolic power(33,34) and muscle activity(35) typically decrease, with steady state reached after hours or days of practice. For example, Sánchez et al recently showed that split-belt treadmill training takes longer than originally thought(36), and training over multiple sessions can facilitate better learning because memory consolidation occurs during sleep(37).…”

Section: Introductionmentioning

confidence: 99%

Self-selected step length asymmetry is not explained by energy cost minimization in individuals with chronic stroke

Nguyen¹,

Jackson

Aucie

et al. 2019

Preprint

View full text Add to dashboard Cite

Background: Asymmetric gait post-stroke is associated with decreased mobility, yet individuals with chronic stroke often self-select an asymmetric gait despite being capable of walking more symmetrically. The purpose of this study was to test whether self-selected asymmetry could be explained by energy cost minimization. We hypothesized that short-term deviations from self-selected asymmetry would result in increased metabolic energy consumption, despite being associated with long-term rehabilitation benefits. Other studies have found no difference in metabolic rate across different levels of enforced asymmetry among individuals with chronic stroke, but used methods that left some uncertainty to be resolved. Methods: In this study, ten individuals with chronic stroke walked on a treadmill at participant-specific speeds while voluntarily modulating step length asymmetry. We included only participants with significant self-selected asymmetry who were able to significantly alter asymmetry using visual biofeedback. Conditions included targeting zero asymmetry, self-selected asymmetry, and double the self-selected asymmetry. Participants were trained with the biofeedback system in one session, and data were collected in three subsequent sessions with repeated measures. Self-selected asymmetry was consistent across sessions. A similar protocol was conducted among unimpaired participants. Results: Participants with chronic stroke substantially altered step length asymmetry using biofeedback, but this did not affect metabolic rate (ANOVA, p = 0.8). In unimpaired participants, self-selected step length asymmetry was close to zero and corresponded to the lowest energy cost (ANOVA, p = 6e-4). While the symmetry of unimpaired gait may be the result of energy cost minimization, self-selected step length asymmetry in individuals with chronic stroke cannot be explained by a similar least-effort drive. Conclusions: Interventions that encourage changes in step length asymmetry by manipulating metabolic energy consumption may be effective because these therapies would not have to overcome a metabolic penalty for altering asymmetry.

show abstract

Using asymmetry to your advantage: learning to acquire and accept external assistance during prolonged split-belt walking

Cited by 8 publications

References 50 publications

Exploration-based learning of a stabilizing controller predicts locomotor adaptation

Exploration-based learning of a stabilizing controller predicts locomotor adaptation

Adapting gait with asymmetric visual feedback affects deadaptation but not adaptation in healthy young adults

Self-selected step length asymmetry is not explained by energy cost minimization in individuals with chronic stroke

Contact Info

Product

Resources

About