SLS: Impulse and Foot Placement Control in Human Running

Constant-speed human running is not exactly periodic. For instance, the body states of the person during the flight phase fluctuate about a mean value. Despite these noise-like deviations, people are able to run without falling down. Here, we examine how these natural state fluctuations are controlled using ground reaction forces and foot placement during running. We use natural step-to-step variability to infer such control. We find that most of the deviation in the sideways and fore-aft speed at mid-flight is nullified by a corrective impulse in the following foot-strike. In achieving this, people modulate the negative part of the ground reaction force more than the positive part. Further, we find that foot placement is used a control more in the sideways direction than in the fore-aft direction. The methods and results in this work can be used to better understand how such a controller for running differs in professional runners who are more practiced.