Quick foot placement adjustments during gait: direction matters

Abstract

To prevent falls, adjustment of foot placement is a frequently used strategy to regulate and restore gait stability. While foot trajectory adjustments have been studied during discrete stepping, online corrections during walking are more common in daily life. Here, we studied quick foot placement adjustments during gait, using an instrumented treadmill equipped with a projector, which allowed us to project virtual stepping stones. This allowed us to shift some of the approaching stepping stones in a chosen direction at a given moment, such that participants were forced to adapt their step in that specific direction and had varying time available to do so. Thirteen healthy participants performed six experimental trials all consisting of 580 stepping stones, and 96 of those stones were shifted anterior, posterior or lateral at one out of four distances from the participant. Overall, long-step gait adjustments were performed more successfully than short-step and side-step gait adjustments. We showed that the ability to execute movement adjustments depends on the direction of the trajectory adjustment. Our findings suggest that choosing different leg movement adjustments for obstacle avoidance comes with different risks and that strategy choice does not depend exclusively on environmental constraints. The used obstacle avoidance strategy choice might be a trade-off between the environmental factors (i.e., the cost of a specific adjustment) and individuals' ability to execute a specific adjustment with success (i.e., the associated execution risk).

Fast responses to stepping‐target displacements when walking

“…Hand movement adjustments become stronger for perturbations closer to the end of the movement (Oostwoud Wijdenes et al 2013;Smeets et al 2016;Zhang et al 2018), but this may not be so for foot adjustments because strong responses might lead to a loss of balance. In accordance with this possibility, the foot placement adjustments in response to late perturbations have been reported to be incomplete (Hoogkamer et al 2015;Mazaheri et al 2015) rather than stronger. We therefore considered the timing of the perturbation when analysing the data.…”

“…The shift was initiated when the participant's centre of pressure was 65 cm from the stepping target's position. This threshold of 65 cm corresponds to a moment early in the swing phase, and was considered to be a relatively easy level in previous studies (Hoogkamer et al 2015(Hoogkamer et al , 2017Mazaheri et al 2015). As a result of delays in the equipment and variations in gait, the moment of perturbations varied within a range of about 200 ms with respect to the actual foot placement.…”

“…We know that it is possible to elicit foot placement adjustments. Such adjustments are not only found after mechanical perturbations (Hof & Duysens, 2013;Rankin et al 2014;Afschrift et al 2018), but also in response to unexpected obstacles (Moraes et al 2004;Weerdesteyn et al 2004;Potocanac et al 2014b) or to stepping stones being displaced (Bank et al 2011;Peper et al 2012;Young & Hollands, 2012;Hoogkamer et al 2015;Mazaheri et al 2015).…”

Continuously updating one’s predictions underlies successful interception

“…Thus, it is evident that movements are continuously adjusted on the basis of the latest information. This is not only true for arm movements, because stepping movements are also adjusted very quickly, despite the potential risk of losing balance by doing so (Hoogkamer et al 2015;Reynolds and Day 2005). Continuous control is most obviously useful when the circumstances change unpredictably, and especially for movements that take a long time.…”

Lower extremity joint-level responses to pelvis perturbation during human walking

“…These findings suggests some form of proportional swing leg control, but it is unclear whether the swing leg is simply accelerated stronger in the direction of the fall with increasing perturbation magnitude, or if the foot is actively positioned prior to foot contact, in response to a perturbation. Instruction on foot positioning can be provided through targets or stepping stones to make subjects explicitly control the location of the foot 17 , 18 . However, such control does not have to apply when reacting to unexpected perturbations without a distinct foot placement objective.…”