Asymmetry of recurrent dynamics as a function of postural stance

This experiment was setup to investigate the deterministic and stochastic properties of the recurrent dynamics of the center of pressure trajectories of each leg (COP(left) and COP(right)) and whole-body (COP(net)) as a function of different foot positions in postural stance (side-by-side, staggered, and tandem standing) and the availability of visual information. The foot position of postural stance can induce degrees of asymmetry of postural instabilities as well as load on each leg that it was hypothesized would influence the deterministic and stochastic properties of COP fluctuations of each leg and of COP(net). Young adults performed two 60 s trials of quiet standing at each posture-vision condition. The availability of visual information increased COP path length, but had no effect on the recurrent dynamics of COP trajectories. Recurrence quantification analysis showed that recurrence, determinism, and entropy were dependent on the direction (AP/ML) of COP motion and foot position during postural stances. The degree of asymmetry between the left and right leg COP dynamics differed across all postural stances and COP(net) dynamics were more similar to those of the more loaded leg. The cross-recurrence quantification analysis also revealed asymmetries in the coordination coupling of AP/ML under each leg; although, these differences were markedly reduced in tandem postures. The findings support the postulation that the asymmetry generated through mechanical constraints (foot position and load) is related to asymmetrical recurrent dynamics of the individual leg and COP(net) based on the degree of postural instability.