Context expectation influences the gait pattern biomechanics

Abstract

Beyond classical aspects related to locomotion (biomechanics), it has been hypothesized that walking pattern is influenced by a combination of distinct computations including online sensory/perceptual sampling and the processing of expectations (neuromechanics). Here, we aimed to explore the potential impact of contrasting scenarios ("risky and potentially dangerous" scenario; "safe and comfortable" scenario) on walking pattern in a group of healthy young adults. Firstly, and consistently with previous literature, we confirmed that the scenario influences gait pattern when it is recalled concurrently to participants' walking activity (motor interference). More intriguingly, our main result showed that participants' gait pattern is also influenced by the contextual scenario when it is evoked only before the start of walking activity (motor expectation). This condition was designed to test the impact of expectations (risky scenario vs. safe scenario) on gait pattern, and the stimulation that preceded walking activity served as prior. Noteworthy, we combined statistical and machine learning (Support-Vector Machine classifier) approaches to stratify distinct levels of analyses that explored the multi-facets architecture of walking. In a nutshell, our combined statistical and machine learning analyses converge in suggesting that walking before steps is not just a paradox.

Figure 1

Graphical representation of the experimental procedure. The two distinct conditions (MI, ME) are separated by a wash-out period. Timeline (in minutes) is reported. The term “randomized” in the figure means that the order of presentation of MI and ME condition was counter-balanced across participants. In addition, also scenarios (risky, safe) were counter-balanced across participants. This means that the A-D_1 and A-D_2, G + A1 and G + A2, A1 and A2 are used in the figure to refer alternatively to the “risky (safe)” or “safe (risky)” scenario. MI: Motor Interference condition; ME: Motor Expectation condition; MI_B: Motor Interference baseline; ME_B: Motor Expectation baseline; A-D_1: Audio-description (risky/safe); A-D_2: Audio-description (safe/risky); G + A1: Gait + Audio (risky/safe); G + A2: Gait + Audio (safe/risky); A1: Audio (risky/safe); A2: Audio (safe/risky); G: Gait; W: Wash-out.

Figure 2

Graphical representation of parameters for which BR as well as SR are statistically significant for both MI and ME condition (corresponding to the parameters on white background in Table 1). [Top panel] [1]: Spatio-temporal parameters (left, [a1]), kinetics curves (middle, [b1]) and kinematics curves (right, [c1]) are reported. The “X” symbols highlight statistically significant differences in the amplitude of peaks, while the yellow bars refer to the statistically significant differences in the timing of peaks. Gray bar in [c1] indicates statistical significance for the range of motion (ROM) value. Curves illustratively refer to the MI condition (accordingly, they are depicted with red nuances. See below). Please, note that the illustration depicts a specific subset of parameters satisfying the “risky-scenario-driven” approach (i.e., BR as well as SR are statistically significant both for MI and ME, corresponding to the parameters on white background in Table 1). [Bottom panel, Left part] [a2]: Illustrative spatio-temporal data. Violin plot of the step length parameter for the MI (red) and ME (blue) condition; shade of red/blue are used for the safe (light), baseline (medium), and the risky (dark) scenarios. [Bottom panel, Middle part and Right part]: Illustrative kinetic data [b2]. Curves representing the power of the knee during flexo-extension in the MI condition (up), and in the ME condition (down). Illustrative kinematic data [c2]. Curves representing the hip flexo-extension in MI condition (up), and in the ME condition (down). For both kinetic and kinematic illustrative data, each curve represents the median curve considering 32 participants. Distinct “colors + type of line” combinations refer to the distinct conditions and scenarios (for MI: dark red + dots = risky; medium red + dashed line = baseline; light red + line = safe) (for ME: dark blue + dots = risky; medium blue + dashed line = baseline; light blue + line = safe). The areas in the background are the interquartile ranges. The “X” symbols highlight statistically significant differences in the amplitude of peaks, while the yellow bars refer to the statistically significant differences in the timing of peaks. MI: Motor Interference condition, ME: Motor Expectation condition, B: Baseline, R: Risky scenario, S: Safe scenario.