Crowd density as an enabling constraint: reorganization of locomotor temporal dynamics in virtual environments

Introduction Locomotion in everyday environments requires humans to coordinate their movements with dynamically structured social contexts such as crowds, yet little is known about how such environments influence the temporal organization of gait. This study investigated whether increasing virtual crowd density reorganizes the temporal dynamics of locomotion in community-dwelling middle-aged and older adults. Methods Twenty adults (aged 55–81 years) performed stepping-in-place locomotion in immersive virtual reality under three conditions: a control condition without avatars, a simple crowd with a small number of approaching avatars, and a complex crowd with higher avatar density. Step interval time series were obtained from lumbar acceleration, and locomotor dynamics were quantified using the coefficient of variation as an index of variability magnitude and the scaling exponent from detrended fluctuation analysis as an index of temporal correlations. Results Generalized linear mixed models showed that, relative to the no-avatar control, the complex crowd condition was associated with reduced variability magnitude and weaker temporal correlations. Discussion The findings suggest that socially structured virtual environments can induce a more stable yet less temporally persistent stepping pattern. In other words, successive steps became less tightly constrained by earlier fluctuations and could be adjusted more flexibly in response to the immediate context, rather than simply reflecting destabilization of stepping behavior. The findings indicate that virtual crowd environments can function as enabling constraints that reorganize locomotor temporal dynamics without compromising stability, and they highlight immersive virtual reality as a useful tool for probing and potentially training adaptive locomotor control in aging populations.