Walking in circles: A modelling approach

Abstract

Blindfolded or disoriented people have the tendency towalk in circles rather than on a straight line even if they wanted to. Here, we use a minimalistic walking model to examine this phenomenon.The bipedal spring-loaded inverted pendulum exhibits asymptotically stable gaitswith centre ofmass (CoM) dynamics and ground reaction forces similar to humanwalking in the sagittal plane.We extend thismodel into three dimensions, and showthat stablewalking patterns persist if the leg is alignedwith respect to the body (here:CoMvelocity) instead of aworld reference frame. Further, we demonstrate that asymmetric leg configurations, which arecommon in humans,will typically lead towalking in circles. The diameter of these circles depends strongly on parameter configuration, but is in line with empirical data from human walkers. Simulation results suggest that walking radius and especially direction of rotation are highly dependent on leg configuration and walking velocity, which explains inconsistent veering behaviour in repeated trials in human data. Finally, we discuss the relation between findings in the model and implications for human walking.