Sara Van Deun

Relationship of Chronic Ankle Instability to Muscle Activation Patterns During the Transition From Double-Leg to Single-Leg Stance

Background Impaired muscle activation may predispose subjects to develop chronic ankle instability. It has been suggested that impairments are found not only in structures around the injured ankle but also around the more proximal joint complexes. Hypothesis Subjects with chronic ankle instability were expected to show later onset times for lower limb and trunk muscle activation when compared with control subjects. They were expected to show less variability in muscle activation patterns compared with the control group. Study Design Controlled laboratory study. Methods Thirty control subjects and 10 subjects with chronic ankle instability participated in the study. The onset of muscle activity of 14 muscles of the lower limb and trunk was measured during the transition from a double-leg stance position to a single-leg stance position in eyes-open and eyes-closed test conditions. Results Subjects with chronic ankle instability showed significantly later onset times for the ankle, hip, and hamstring muscles compared with control subjects. They used a similar muscle activation pattern in both test conditions, whereas control subjects adjusted their activation pattern according to the condition. Conclusions Differences in muscle activation patterns between subjects with chronic ankle instability and control subjects occur not only around the ankle but also around other joints. Subjects with chronic ankle instability show less variability in muscle activation patterns between test conditions. Clinical Relevance Knowledge of muscle activation patterns in the whole lower limb and trunk in noninjured subjects and the differences found in chronic ankle instability subjects broadens the physical therapy approach to the treatment of chronic ankle instability.

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.

Stability of Measurement Outcomes for Voluntary Task Performance in Participants With Chronic Ankle Instability and Healthy Participants

CONTEXT Acceptable measurement stability during data collection is critically important to research. To interpret differences in measurement outcomes among participants or changes within participants after an intervention program, we need to know whether the measurement is stable and consistent. OBJECTIVE To determine the within-session stability of muscle activation patterns for a voluntary postural-control task in a group of noninjured participants and a group of participants with chronic ankle instability (CAI). DESIGN Descriptive laboratory study. SETTING Musculoskeletal laboratory. PATIENTS OR OTHER PARTICIPANTS Twenty control participants (8 men, 12 women; age = 21.8 ± 2.4 years, height = 164.3 ± 13.4 cm, mass = 68.4 ± 17.9 kg) and 20 participants with CAI (12 men, 8 women; age = 21.2 ± 2.1 years, height = 176 ± 10.2 cm, mass = 71.7 ± 11.3 kg). INTERVENTION(S) Participants performed 4 barefoot standing trials, each of which included a 30-second double-legged stance followed by a 30-second single-legged stance in 3 conditions: with vision, without vision, and with vision on a balance pad. MAIN OUTCOME MEASURE(S) The activity of 7 muscles of the lower limb was measured for the stance task in the 3 different conditions for each trial. The onset of muscle activity and muscle recruitment order were determined and compared between the first and the fourth trials for both groups and for each condition. RESULTS We found no differences in the onset of muscle activity among trials for both groups or for each condition. The measurement error was 0.9 seconds at maximum for the control group and 0.12 seconds for the CAI group. In the control group, 70% to 80% of the participants used the same muscle recruitment order in both trials. In the CAI group, 75% to 90% used the same recruitment order. CONCLUSIONS Within 1 session, measurement stability for this task was acceptable for use in further research. Furthermore, no differences were found in measurement stability across conditions in the control or CAI groups.