Interpersonal synchronization during side by side treadmill walking is influenced by leg length differential and altered sensory feedback

Unintentional synchronization of stepping occurs frequently between two people walking side by side, yet little is known regarding the neurological and biomechanical mechanisms that underlie this coupling. The purpose of this study was to quantify the relationship between leg length differential, select variables related to sensory feedback, and unintentional, interpersonal synchronization during gait.MethodsTwenty pairs of participants stepped on side by side treadmills under six different conditions in which visual, auditory, and tactile feedback were altered.ResultsWhen compared with an estimate of synchronization expected to occur by chance, synchronization of stepping was significantly greater in each sensory condition examined. Overall, 62% of pairs exhibited unintentional step frequency locking. Pairs that exhibited entrainment had significantly lower leg length differences between partners (independent t-test, p = .044), and a significant relationship was found between leg length difference and both difference in frequency of stepping (R2 = .258, p < .022) and frequency locking (R2 = 0.307, p = .011). Altering sensory information appeared to have little effect on the amount of step frequency locking, but improved phase angle locking. Specifically, the addition of a mechanical coupling between participants resulted in a significant increase in the amount of time spent phase locked when compared with the case where normal vision and sound were restricted between participants.DiscussionThese data suggest that unintentional gait entrainment can be reproduced in a laboratory setting using side by side treadmills, and that anthropometric properties, such as leg length, have a significant effect on gait synchronization. Further, alterations in sensory information can affect unintentional, interpersonal synchronization, but this behavior appears to be relatively robust to changes in sensory feedback pathways related to gait.