Optimism Persists when Walking in Unpredictable Environments

Abstract

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.

Gait Compensation Strategies to Expected and Unexpected Yielding Terrain

“…The consistent patterns observed in these behaviours indicate that these strategies are in uenced by prior experiences, as previously observed by Patla 1 and supported by recent literature [17][18][19]21,22 . These ndings provide a valuable database for further investigations involving children and individuals with pathological conditions.…”

“…We can formulate a hypothesis that when the foot engages with the perturbation, both Anticipatory and Predictive strategies come into play to select the most suitable course of action. They work in tandem, much like Reactive and Predictive strategies do when individuals are exposed to continually unpredictable environments 22 .…”

“…Different research groups have examined adaptation to uneven terrain through electromyography 19 and centre of mass analysis 20 . Furthermore, Bunz and colleagues employed a neuromusculoskeletal model to predict preactivation re exes during walking on rough terrain 21 , and Bucklin and colleagues studied adaptive behaviour during unpredictable lateral pelvis perturbations on a treadmill 22 . Taylor and colleagues described perturbation effects through treadmill manipulation, albeit with limited reporting of spatiotemporal parameters 23 .…”