Sway activity and muscle recruitment order during transition from double to single-leg stance in subjects with chronic ankle instability

Subjects with CAI (chronic ankle instability) are slower in activating their leg muscles when shifting weight (from double to single leg stance; DLS and SLS). We examined if these delays are associated with longer transition/stabilization times. This was tested by analyzing the center of pressure (COP) trajectory data (1) in the DLS phase before onset of transition, (2) in the quasi-stable phase of the SLS, immediately after the transition phase but before time to stabilization (TTS) and (3) in the SLS phase after TTS. Data were recorded from 20 subjects with CAI and 20 controls. The TTS was longer for the CAIs than for controls (3.25 vs. 2.28 s in EO and 3.41 vs. 2.51 s in EC; p < 0.001). Similarly, the time of transition (TTR) was prolonged in CAIs (1.48 vs. 1.14 s in EO and 1.53 vs. 1.20 s in EC; p < 0.05). These prolonged periods came in parallel with an increase in the ML sway in the quasi-stable phase (mean displacement 2.20 vs. 1.75 cm in EO; 3.37 vs. 2.62 cm in EC; significant for EC p < 0.05). The TTR in CAIs was positively correlated with time onsets of the adductor longus muscle during transitions with EC (R = 0.51, p = 0.03). The findings support the use of a weight-shifting paradigm for the evaluation of balance control in CAI. Specifically, we underscore the transition phase and quasi-stable phase of the SLS as promising time windows for documenting balance control deficits in CAI. (C) 2012 Elsevier B.V. All rights reserved.