Deficits in time-to-boundary measures of postural control with chronic ankle instability.

Our purpose was to examine postural control in single leg stance in subjects with and without unilateral chronic ankle instability (CAI) using traditional center of pressure (COP)-based and time-to-boundary (TTB) measures. Fifteen physically active females with self-reported unilateral chronic ankle instability (CAI) and nine healthy female controls performed three 10-s trials of eyes open single limb quiet standing on a force plate on both their legs. The traditional measures were mean COP velocity, standard deviation of COP, range of COP, and percent of available range utilized. The TTB measures were absolute minimum TTB, mean of the minimum TTB samples, and standard deviation of the minimum TTB samples. All measures were calculated in both the mediolateral (ML) and anteroposterior (AP) directions. A 2x2 group (CAI, control) by side (involved, uninvolved) design was utilized. The CAI group had significantly lower scores for five of the six TTB measures compared to the control group, however only one (AP COP velocity) of the eight traditional measures was different between groups. The TTB measures appear to detect postural control deficits related to CAI that traditional measures do not.