Stability limits in the assessment of postural control through the Time-to-boundary function.

The extraction of the Time-to-boundary function (TtB) from CoP data in upright stance trials has recently gained much attention. In this contribution, some parameters extracted from TtB in unperturbed upright stance trials were analysed in terms of variability with respect to different hypothesized stability limits. In particular, nonlinear stability factors were analyzed as a function of the different values for the boundary limits through which TtB is calculated. A sample population of 5 healthy young adults underwent upright stance trials in different conditions. The amplitude nonlinear stability factors showed a strong dependency with the boundary limits, which on the contrary did not affect the rhythmical nonlinear stability factors.