Altered Muscle Activation Patterns During Unexpected Single-leg Landing In Chronic Ankle Instability Patients

Abstract

Chronic ankle instability (CAI) patients display altered motor controls during inversion perturbation. Although these alterations may be vulnerable motor controls compared to controls, inversion perturbation under anticipatory conditions makes a less realistic simulation of lateral ankle sprains. PURPOSE: To examine differences in muscle activation during an unexpected inversion perturbation among CAI, coper, and control groups. METHODS: Twenty-two CAI patients (M = 11, F = 11; 22 ± 3 yr, 174 ± 8 cm, 71 ± 10 kg), 22 controls (M = 11, F = 11; 21 ± 2 yr, 173 ± 7 cm, 71 ± 10 kg), and 22 copers (M = 11, F = 11; 21 ± 2 yr, 174 ± 8 cm, 70 ± 13 kg) participated. Participants completed 5 trials of unexpected ankle inversion perturbation during single-leg landing onto a tilted force platform (25º) from a height of 30 cm. EMG data of tibialis anterior (TA), peroneus longus (PL), medial gastrocnemius (MG), and gluteus maximus (GX) were collected from 200 ms before and after initial contact (IC). Functional linear models were used to detect between-group differences. If 95% CIs did not cross zero, differences were significant. RESULTS: Figure 1 shows that CAI patients displayed greater TA and MG activation before IC relative to copers and/or controls. In addition, CAI patients showed greater TA and PL activation after IC relative to copers and/or controls. Copers and controls had similar muscle activation patterns. CONCLUSION: While copers and controls showed similar muscle activation during unexpected ankle perturbation, increased TA and MG activation prior to IC in CAI patients may indicate a neuromuscular effort to stabilize the ankle to prevent further sprains. Increased TA and PL activation after IC in CAI patients may also represent a protective motor control to prevent excessive displacement of the rear foot from the inversion perturbation. However, similar patterns in copers and controls seem to elicit coping mechanisms in an attempt to prevent further injuries after their initial injuries.