Fig 1.
Mechanisms to maintain balance during locomotion in the frontal plain.
Panel (A) shows the biomechanics of the upright body during locomotion under the simplifying inverted pendulum assumption. The horizontal CoM accelerates away from the CoP, with the magnitude of the acceleration proportional to the distance between the two. The lower panels illustrate how the CoP can be modified during walking. (B) At each new step, the lateral foot placement can be adjusted, shifting the CoP throughout the following stance phase. (C) During single stance, the CoP can be adjusted within the limits of the stance foot sole. (D) Foot placement changes are mainly accomplished by hip ab-/adduction of the swing leg, (E) lateral rolling of the stance foot by the ankle musculature.
Table 1.
Model parameters used in the simulations.
Fig 2.
Histograms of the step response for the experimental data.
Panel (A) shows the step response S, panel (B) shows the stimulus response for stimulus conditions LEFT (blue, N = 434) and RIGHT (yellow, N = 433). Solid lines are best fits with Gaussians, dashed lines indicate the mean for each stimulus condition.
Fig 3.
Response of the medial-lateral stance foot CoP and swing foot position from the experimental data.
Panel (A) shows the CoP response, panel (B) the response of the swing foot heel. Normalized time ranges from stimulus onset to touchdown of the first step. Significant differences of the CoP response from zero at each time step are marked by blue (LEFT, N = 434) and yellow (RIGHT, N = 433) asterisks. The thin grey lines indicate the linear fits of the responses at the points of maximal rate of change, the intersection of these fits is the estimate of the response onset. Error bars indicate 95% confidence intervals.
Fig 4.
Histograms of the step response for the model simulations.
Panel (A) shows the step response S, panel (B) shows the stimulus response for stimulus conditions LEFT (blue) and RIGHT (yellow). Solid lines are best fits with Gaussians, dashed lines indicate the mean for each stimulus condition.
Fig 5.
CoP response for the model simulations.
Response of the medial-lateral stance foot CoP to LEFT (blue) and RIGHT (yellow) stimuli from the model simulations. Time ranges from stimulus onset to touchdown of the first step. Error bars indicate 95% confidence intervals.
Fig 6.
Step response changes with different mechanisms in the model.
Step response to LEFT (blue) and RIGHT (yellow) stimuli from the model simulations. The top represents results from the controller without the CoP shift mechanism, the bottom results from the controller with the CoP shift mechanism.