Human walking has been studied extensively, but there has been less work on how people adapt their gaits while coupled by a mechanical link such as carrying an object together.
Jessica Lanini from the École Polytechnique Fédérale de Lausanne in Switzerland and her team of researchers investigated one case of interactive locomotion with six people (four men and two women) who were grouped into seven pairs that walked one in front of the other while carrying a rigid, stretcher-like object between them. Each pair did two trials that entailed walking 12 meters two times (that is, back and forth) without the stretcher-like object, and another two trials while carrying the object, which was 150 centimeters long and weighed 8 kilograms. The researchers analyzed the pairs’ adaptation of walking gaits and coordination of footfall patterns. In addition, they used a simple computer model — two bipedal agents connected with a spring-damper — for mechanical analysis of the interactive locomotion.
The researchers found that being mechanically coupled by the stretcher-like object changed peoples’ walking gaits and reduced step length and speed of movement. In addition, subjects carrying the stretcher-like object coordinated their footfall patterns in more than 70 percent of the experiments, synchronizing in a way that is reminiscent of gaits used by four-legged animals.
The simple model predicted some locomotion characteristics of two people coupled by a mechanical link, including the preference for synchronized gaits as well as some footfall patterns associated with quadrupedal gaits (in particular, pace and trot gaits). The researchers suggest that the observed synchronization of people carrying objects together can be explained by passive mechanical properties rather than high-level control strategies such as foot placement. However, they also say that other features of the paired walking gait might be related to cognitive and/or psychological effects, and that more complex motor control actions likely should be considered to better understand this phenomenon.
Reference: Lanini J, Duburcq A, Razavi H, Le Goff CG, Ijspeert AJ (2017) Interactive locomotion: Investigation and modeling of physically-paired humans while walking. PLoS ONE 12(9): e0179989. https://doi.org/10.1371/journal.pone.0179989
Image Credit: Lanini et al (2017)