What guides the selection of alternate foot placement during locomotion in humans

Abstract

Our goal was to understand the bases for selection of alternate foot placement during locomotion when the normal landing area is undesirable. In this study, a light spot of different shapes and sizes simulated an undesirable landing area. Participants were required to avoid stepping on this spot under different time constraints. Alternate chosen foot placements were categorised into one of eight choices. Results showed that selection of alternate foot placement is systematic. There is a single dominant choice for each combination of light spot and normal landing spot. The dominant choice minimises the displacement of the foot from its normal landing spot (less than half a foot length). If several response choices satisfy this criterion, three selection strategies are used to guide foot placement: placing the foot in the plane of progression, choosing to take a longer step over a shorter step and selecting a medial rather than lateral foot placement. All these alternate foot-placement choices require minimal changes to the ongoing locomotor muscle activity, pose minimal threat to dynamic stability, allow for quick initiation of change in ongoing movement and ensure that the locomotor task runs without interruption. Thus, alternate foot-placement choices are dependent not only on visual input about the location, size and shape of the undesirable surface, but also on the relationship between the characteristics of the undesirable surface and the normal landing area.

Stick insect locomotion in a complex environment: climbing over large gaps

“…In humans, different obstacle avoidance reactions result in lengthening or shortening a step if enough time is available to adapt the step length (Patla et al, 1991). If the obstacle is perceived within the same step cycle, lengthening the step is the preferred strategy (Patla et al, 1999). Comparing 30·mm to 50·mm gap-crossing trials revealed that most differences occur during section EFL.…”

“…In vertebrates such as humans, obstacle avoidance behaviour during walking is mainly guided by vision (Patla et al, 1999). In insects, orientation of the antennae towards visual stimuli has been observed (Honegger, 1981).…”

A model for selecting alternate foot placement during human locomotion.

“…Previous studies showed that the selection of alternate foot placement is based on visual inputs and predictions of future foot placement combined with a set of internal rules that are guided by three determinants: minimum foot displacement, stability, and the maintenance of forward progression (Patla et al, 1999;Moraes et al, 2004). The present review defines and provides evidence to support this model.…”

“…This information needs to be coupled with prediction of the foot's normal landing position. Patla et al (1999) proposed that interactions between visual and proprioceptive inputs and step-cycle control are used to estimate the normal landing position of the foot. A mechanism by which this visual and proprioceptive information can be integrated to estimate future foot placement is the forward internal model (Wolpert, Ghahramani, & Jordan, 1995).…”

“…There is a preference for changes in the plane of progression over changes in the frontal plane (Patla et al, 1999). Moraes et al (2004) observed that changes in the frontal plane are accompanied by foot placement that is located more forward to minimize deviation from the forward goal.…”